PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

EX(1P)                    POSIX Programmer's Manual                   EX(1P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       ex — text editor

SYNOPSIS         top

       ex [−rR] [−s|−v] [−c command] [−t tagstring] [−w size] [file...]

DESCRIPTION         top

       The ex utility is a line-oriented text editor. There are two other
       modes of the editor—open and visual—in which screen-oriented editing
       is available. This is described more fully by the ex open and visual
       commands and in vi(1p).

       If an operand is '−', the results are unspecified.

       This section uses the term edit buffer to describe the current
       working text. No specific implementation is implied by this term. All
       editing changes are performed on the edit buffer, and no changes to
       it shall affect any file until an editor command writes the file.

       Certain terminals do not have all the capabilities necessary to
       support the complete ex definition, such as the full-screen editing
       commands (visual mode or open mode).  When these commands cannot be
       supported on such terminals, this condition shall not produce an
       error message such as ``not an editor command'' or report a syntax
       error. The implementation may either accept the commands and produce
       results on the screen that are the result of an unsuccessful attempt
       to meet the requirements of this volume of POSIX.1‐2008 or report an
       error describing the terminal-related deficiency.

OPTIONS         top

       The ex utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines, except for the
       unspecified usage of '−', and that '+' may be recognized as an option
       delimiter as well as '−'.

       The following options shall be supported:

       −c command
                 Specify an initial command to be executed in the first edit
                 buffer loaded from an existing file (see the EXTENDED
                 DESCRIPTION section).  Implementations may support more
                 than a single −c option. In such implementations, the
                 specified commands shall be executed in the order specified
                 on the command line.

       −r        Recover the named files (see the EXTENDED DESCRIPTION
                 section).  Recovery information for a file shall be saved
                 during an editor or system crash (for example, when the
                 editor is terminated by a signal which the editor can
                 catch), or after the use of an ex preserve command.

                 A crash in this context is an unexpected failure of the
                 system or utility that requires restarting the failed
                 system or utility. A system crash implies that any
                 utilities running at the time also crash. In the case of an
                 editor or system crash, the number of changes to the edit
                 buffer (since the most recent preserve command) that will
                 be recovered is unspecified.

                 If no file operands are given and the −t option is not
                 specified, all other options, the EXINIT variable, and any
                 .exrc files shall be ignored; a list of all recoverable
                 files available to the invoking user shall be written, and
                 the editor shall exit normally without further action.

       −R        Set readonly edit option.

       −s        Prepare ex for batch use by taking the following actions:

                  *  Suppress writing prompts and informational (but not
                     diagnostic) messages.

                  *  Ignore the value of TERM and any implementation default
                     terminal type and assume the terminal is a type
                     incapable of supporting open or visual modes; see the
                     visual command and the description of vi(1p).

                  *  Suppress the use of the EXINIT environment variable and
                     the reading of any .exrc file; see the EXTENDED
                     DESCRIPTION section.

                  *  Suppress autoindentation, ignoring the value of the
                     autoindent edit option.

       −t tagstring
                 Edit the file containing the specified tagstring; see
                 ctags(1p).  The tags feature represented by −t tagstring
                 and the tag command is optional. It shall be provided on
                 any system that also provides a conforming implementation
                 of ctags; otherwise, the use of −t produces undefined
                 results. On any system, it shall be an error to specify
                 more than a single −t option.

       −v        Begin in visual mode (see vi(1p)).

       −w size   Set the value of the window editor option to size.

OPERANDS         top

       The following operand shall be supported:

       file      A pathname of a file to be edited.

STDIN         top

       The standard input consists of a series of commands and input text,
       as described in the EXTENDED DESCRIPTION section. The implementation
       may limit each line of standard input to a length of {LINE_MAX}.

       If the standard input is not a terminal device, it shall be as if the
       −s option had been specified.

       If a read from the standard input returns an error, or if the editor
       detects an end-of-file condition from the standard input, it shall be
       equivalent to a SIGHUP asynchronous event.

INPUT FILES         top

       Input files shall be text files or files that would be text files
       except for an incomplete last line that is not longer than
       {LINE_MAX}−1 bytes in length and contains no NUL characters. By
       default, any incomplete last line shall be treated as if it had a
       trailing <newline>.  The editing of other forms of files may
       optionally be allowed by ex implementations.

       The .exrc files and source files shall be text files consisting of ex
       commands; see the EXTENDED DESCRIPTION section.

       By default, the editor shall read lines from the files to be edited
       without interpreting any of those lines as any form of editor
       command.

ENVIRONMENT VARIABLES         top

       The following environment variables shall affect the execution of ex:

       COLUMNS   Override the system-selected horizontal screen size. See
                 the Base Definitions volume of POSIX.1‐2008, Chapter 8,
                 Environment Variables for valid values and results when it
                 is unset or null.

       EXINIT    Determine a list of ex commands that are executed on editor
                 start-up. See the EXTENDED DESCRIPTION section for more
                 details of the initialization phase.

       HOME      Determine a pathname of a directory that shall be searched
                 for an editor start-up file named .exrc; see the EXTENDED
                 DESCRIPTION section.

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base Definitions
                 volume of POSIX.1‐2008, Section 8.2, Internationalization
                 Variables for the precedence of internationalization
                 variables used to determine the values of locale
                 categories.)

       LC_ALL    If set to a non-empty string value, override the values of
                 all the other internationalization variables.

       LC_COLLATE
                 Determine the locale for the behavior of ranges,
                 equivalence classes, and multi-character collating elements
                 within regular expressions.

       LC_CTYPE  Determine the locale for the interpretation of sequences of
                 bytes of text data as characters (for example, single-byte
                 as opposed to multi-byte characters in arguments and input
                 files), the behavior of character classes within regular
                 expressions, the classification of characters as uppercase
                 or lowercase letters, the case conversion of letters, and
                 the detection of word boundaries.

       LC_MESSAGES
                 Determine the locale that should be used to affect the
                 format and contents of diagnostic messages written to
                 standard error.

       LINES     Override the system-selected vertical screen size, used as
                 the number of lines in a screenful and the vertical screen
                 size in visual mode.  See the Base Definitions volume of
                 POSIX.1‐2008, Chapter 8, Environment Variables for valid
                 values and results when it is unset or null.

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.

       PATH      Determine the search path for the shell command specified
                 in the ex editor commands !, shell, read, and write, and
                 the open and visual mode command !; see the description of
                 command search and execution in Section 2.9.1.1, Command
                 Search and Execution.

       SHELL     Determine the preferred command line interpreter for use as
                 the default value of the shell edit option.

       TERM      Determine the name of the terminal type. If this variable
                 is unset or null, an unspecified default terminal type
                 shall be used.

ASYNCHRONOUS EVENTS         top

       The following term is used in this and following sections to specify
       command and asynchronous event actions:

       complete write
                 A complete write is a write of the entire contents of the
                 edit buffer to a file of a type other than a terminal
                 device, or the saving of the edit buffer caused by the user
                 executing the ex preserve command. Writing the contents of
                 the edit buffer to a temporary file that will be removed
                 when the editor exits shall not be considered a complete
                 write.

       The following actions shall be taken upon receipt of signals:

       SIGINT    If the standard input is not a terminal device, ex shall
                 not write the file or return to command or text input mode,
                 and shall exit with a non-zero exit status.

                 Otherwise, if executing an open or visual text input mode
                 command, ex in receipt of SIGINT shall behave identically
                 to its receipt of the <ESC> character.

                 Otherwise:

                  1. If executing an ex text input mode command, all input
                     lines that have been completely entered shall be
                     resolved into the edit buffer, and any partially
                     entered line shall be discarded.

                  2. If there is a currently executing command, it shall be
                     aborted and a message displayed. Unless otherwise
                     specified by the ex or vi command descriptions, it is
                     unspecified whether any lines modified by the executing
                     command appear modified, or as they were before being
                     modified by the executing command, in the buffer.

                     If the currently executing command was a motion
                     command, its associated command shall be discarded.

                  3. If in open or visual command mode, the terminal shall
                     be alerted.

                  4. The editor shall then return to command mode.

       SIGCONT   The screen shall be refreshed if in open or visual mode.

       SIGHUP    If the edit buffer has been modified since the last
                 complete write, ex shall attempt to save the edit buffer so
                 that it can be recovered later using the −r option or the
                 ex recover command. The editor shall not write the file or
                 return to command or text input mode, and shall terminate
                 with a non-zero exit status.

       SIGTERM   Refer to SIGHUP.

       The action taken for all other signals is unspecified.

STDOUT         top

       The standard output shall be used only for writing prompts to the
       user, for informational messages, and for writing lines from the
       file.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       The output from ex shall be text files.

EXTENDED DESCRIPTION         top

       Only the ex mode of the editor is described in this section. See
       vi(1p) for additional editing capabilities available in ex.

       When an error occurs, ex shall write a message. If the terminal
       supports a standout mode (such as inverse video), the message shall
       be written in standout mode. If the terminal does not support a
       standout mode, and the edit option errorbells is set, an alert action
       shall precede the error message.

       By default, ex shall start in command mode, which shall be indicated
       by a : prompt; see the prompt command. Text input mode can be entered
       by the append, insert, or change commands; it can be exited (and
       command mode re-entered) by typing a <period> ('.')  alone at the
       beginning of a line.

   Initialization in ex and vi
       The following symbols are used in this and following sections to
       specify locations in the edit buffer:

       alternate and current pathnames
             Two pathnames, named current and alternate, are maintained by
             the editor. Any ex commands that take filenames as arguments
             shall set them as follows:

              1. If a file argument is specified to the ex edit, ex, or
                 recover commands, or if an ex tag command replaces the
                 contents of the edit buffer.

                  a. If the command replaces the contents of the edit
                     buffer, the current pathname shall be set to the file
                     argument or the file indicated by the tag, and the
                     alternate pathname shall be set to the previous value
                     of the current pathname.

                  b. Otherwise, the alternate pathname shall be set to the
                     file argument.

              2. If a file argument is specified to the ex next command:

                  a. If the command replaces the contents of the edit
                     buffer, the current pathname shall be set to the first
                     file argument, and the alternate pathname shall be set
                     to the previous value of the current pathname.

              3. If a file argument is specified to the ex file command, the
                 current pathname shall be set to the file argument, and the
                 alternate pathname shall be set to the previous value of
                 the current pathname.

              4. If a file argument is specified to the ex read and write
                 commands (that is, when reading or writing a file, and not
                 to the program named by the shell edit option), or a file
                 argument is specified to the ex xit command:

                  a. If the current pathname has no value, the current
                     pathname shall be set to the file argument.

                  b. Otherwise, the alternate pathname shall be set to the
                     file argument.

             If the alternate pathname is set to the previous value of the
             current pathname when the current pathname had no previous
             value, then the alternate pathname shall have no value as a
             result.

       current line
             The line of the edit buffer referenced by the cursor. Each
             command description specifies the current line after the
             command has been executed, as the current line value.  When the
             edit buffer contains no lines, the current line shall be zero;
             see Addressing in ex.

       current column
             The current display line column occupied by the cursor. (The
             columns shall be numbered beginning at 1.) Each command
             description specifies the current column after the command has
             been executed, as the current column value. This column is an
             ideal column that is remembered over the lifetime of the
             editor. The actual display line column upon which the cursor
             rests may be different from the current column; see the cursor
             positioning discussion in Command Descriptions in vi.

       set to non-<blank>
             A description for a current column value, meaning that the
             current column shall be set to the last display line column on
             which is displayed any part of the first non-<blank> of the
             line. If the line has no non-<blank> non-<newline> characters,
             the current column shall be set to the last display line column
             on which is displayed any part of the last non-<newline>
             character in the line. If the line is empty, the current column
             shall be set to column position 1.

       The length of lines in the edit buffer may be limited to {LINE_MAX}
       bytes. In open and visual mode, the length of lines in the edit
       buffer may be limited to the number of characters that will fit in
       the display. If either limit is exceeded during editing, an error
       message shall be written. If either limit is exceeded by a line read
       in from a file, an error message shall be written and the edit
       session may be terminated.

       If the editor stops running due to any reason other than a user
       command, and the edit buffer has been modified since the last
       complete write, it shall be equivalent to a SIGHUP asynchronous
       event. If the system crashes, it shall be equivalent to a SIGHUP
       asynchronous event.

       During initialization (before the first file is copied into the edit
       buffer or any user commands from the terminal are processed) the
       following shall occur:

        1. If the environment variable EXINIT is set, the editor shall
           execute the ex commands contained in that variable.

        2. If the EXINIT variable is not set, and all of the following are
           true:

            a. The HOME environment variable is not null and not empty.

            b. The file .exrc in the directory referred to by the HOME
               environment variable:

                i.  Exists

               ii.  Is owned by the same user ID as the real user ID of the
                    process or the process has appropriate privileges

               iii. Is not writable by anyone other than the owner

           the editor shall execute the ex commands contained in that file.

        3. If and only if all of the following are true:

            a. The current directory is not referred to by the HOME
               environment variable.

            b. A command in the EXINIT environment variable or a command in
               the .exrc file in the directory referred to by the HOME
               environment variable sets the editor option exrc.

            c. The .exrc file in the current directory:

                i.  Exists

               ii.  Is owned by the same user ID as the real user ID of the
                    process, or by one of a set of implementation-defined
                    user IDs

               iii. Is not writable by anyone other than the owner

           the editor shall attempt to execute the ex commands contained in
           that file.

       Lines in any .exrc file that are blank lines shall be ignored. If any
       .exrc file exists, but is not read for ownership or permission
       reasons, it shall be an error.

       After the EXINIT variable and any .exrc files are processed, the
       first file specified by the user shall be edited, as follows:

        1. If the user specified the −t option, the effect shall be as if
           the ex tag command was entered with the specified argument, with
           the exception that if tag processing does not result in a file to
           edit, the effect shall be as described in step 3. below.

        2. Otherwise, if the user specified any command line file arguments,
           the effect shall be as if the ex edit command was entered with
           the first of those arguments as its file argument.

        3. Otherwise, the effect shall be as if the ex edit command was
           entered with a nonexistent filename as its file argument. It is
           unspecified whether this action shall set the current pathname.
           In an implementation where this action does not set the current
           pathname, any editor command using the current pathname shall
           fail until an editor command sets the current pathname.

       If the −r option was specified, the first time a file in the initial
       argument list or a file specified by the −t option is edited, if
       recovery information has previously been saved about it, that
       information shall be recovered and the editor shall behave as if the
       contents of the edit buffer have already been modified. If there are
       multiple instances of the file to be recovered, the one most recently
       saved shall be recovered, and an informational message that there are
       previous versions of the file that can be recovered shall be written.
       If no recovery information about a file is available, an
       informational message to this effect shall be written, and the edit
       shall proceed as usual.

       If the −c option was specified, the first time a file that already
       exists (including a file that might not exist but for which recovery
       information is available, when the −r option is specified) replaces
       or initializes the contents of the edit buffer, the current line
       shall be set to the last line of the edit buffer, the current column
       shall be set to non-<blank>, and the ex commands specified with the
       −c option shall be executed. In this case, the current line and
       current column shall not be set as described for the command
       associated with the replacement or initialization of the edit buffer
       contents. However, if the −t option or a tag command is associated
       with this action, the −c option commands shall be executed and then
       the movement to the tag shall be performed.

       The current argument list shall initially be set to the filenames
       specified by the user on the command line. If no filenames are
       specified by the user, the current argument list shall be empty. If
       the −t option was specified, it is unspecified whether any filename
       resulting from tag processing shall be prepended to the current
       argument list. In the case where the filename is added as a prefix to
       the current argument list, the current argument list reference shall
       be set to that filename. In the case where the filename is not added
       as a prefix to the current argument list, the current argument list
       reference shall logically be located before the first of the
       filenames specified on the command line (for example, a subsequent ex
       next command shall edit the first filename from the command line). If
       the −t option was not specified, the current argument list reference
       shall be to the first of the filenames on the command line.

   Addressing in ex
       Addressing in ex relates to the current line and the current column;
       the address of a line is its 1-based line number, the address of a
       column is its 1-based count from the beginning of the line.
       Generally, the current line is the last line affected by a command.
       The current line number is the address of the current line. In each
       command description, the effect of the command on the current line
       number and the current column is described.

       Addresses are constructed as follows:

        1. The character '.'  (period) shall address the current line.

        2. The character '$' shall address the last line of the edit buffer.

        3. The positive decimal number n shall address the nth line of the
           edit buffer.

        4. The address "'x" refers to the line marked with the mark name
           character 'x', which shall be a lowercase letter from the
           portable character set, the backquote character, or the single-
           quote character. It shall be an error if the line that was marked
           is not currently present in the edit buffer or the mark has not
           been set. Lines can be marked with the ex mark or k commands, or
           the vi m command.

        5. A regular expression enclosed by <slash> characters ('/') shall
           address the first line found by searching forwards from the line
           following the current line toward the end of the edit buffer and
           stopping at the first line for which the line excluding the
           terminating <newline> matches the regular expression. As stated
           in Regular Expressions in ex, an address consisting of a null
           regular expression delimited by <slash> characters ("//") shall
           address the next line for which the line excluding the
           terminating <newline> matches the last regular expression
           encountered. In addition, the second <slash> can be omitted at
           the end of a command line. If the wrapscan edit option is set,
           the search shall wrap around to the beginning of the edit buffer
           and continue up to and including the current line, so that the
           entire edit buffer is searched. Within the regular expression,
           the sequence "\/" shall represent a literal <slash> instead of
           the regular expression delimiter.

        6. A regular expression enclosed in <question-mark> characters ('?')
           shall address the first line found by searching backwards from
           the line preceding the current line toward the beginning of the
           edit buffer and stopping at the first line for which the line
           excluding the terminating <newline> matches the regular
           expression. An address consisting of a null regular expression
           delimited by <question-mark> characters ("??") shall address the
           previous line for which the line excluding the terminating
           <newline> matches the last regular expression encountered. In
           addition, the second <question-mark> can be omitted at the end of
           a command line. If the wrapscan edit option is set, the search
           shall wrap around from the beginning of the edit buffer to the
           end of the edit buffer and continue up to and including the
           current line, so that the entire edit buffer is searched. Within
           the regular expression, the sequence "\?" shall represent a
           literal <question-mark> instead of the RE delimiter.

        7. A <plus-sign> ('+') or a minus-sign ('−') followed by a decimal
           number shall address the current line plus or minus the number. A
           '+' or '−' not followed by a decimal number shall address the
           current line plus or minus 1.

       Addresses can be followed by zero or more address offsets, optionally
       <blank>-separated.  Address offsets are constructed as follows:

        1. A '+' or '−' immediately followed by a decimal number shall add
           (subtract) the indicated number of lines to (from) the address. A
           '+' or '−' not followed by a decimal number shall add (subtract)
           1 to (from) the address.

        2. A decimal number shall add the indicated number of lines to the
           address.

       It shall not be an error for an intermediate address value to be less
       than zero or greater than the last line in the edit buffer. It shall
       be an error for the final address value to be less than zero or
       greater than the last line in the edit buffer.

       Commands take zero, one, or two addresses; see the descriptions of
       1addr and 2addr in Command Descriptions in ex.  If more than the
       required number of addresses are provided to a command that requires
       zero addresses, it shall be an error. Otherwise, if more than the
       required number of addresses are provided to a command, the addresses
       specified first shall be evaluated and then discarded until the
       maximum number of valid addresses remain.

       Addresses shall be separated from each other by a <comma> (',') or a
       <semicolon> (';').  If no address is specified before or after a
       <comma> or <semicolon> separator, it shall be as if the address of
       the current line was specified before or after the separator. In the
       case of a <semicolon> separator, the current line ('.')  shall be set
       to the first address, and only then will the next address be
       calculated. This feature can be used to determine the starting line
       for forwards and backwards searches (see rules 5. and 6.).

       A <percent-sign> ('%') shall be equivalent to entering the two
       addresses "1,$".

       Any delimiting <blank> characters between addresses, address
       separators, or address offsets shall be discarded.

   Command Line Parsing in ex
       The following symbol is used in this and following sections to
       describe parsing behavior:

       escape    If a character is referred to as ``<backslash>-escaped'' or
                 ``<control>‐V-escaped'', it shall mean that the character
                 acquired or lost a special meaning by virtue of being
                 preceded, respectively, by a <backslash> or <control>‐V
                 character. Unless otherwise specified, the escaping
                 character shall be discarded at that time and shall not be
                 further considered for any purpose.

       Command-line parsing shall be done in the following steps. For each
       step, characters already evaluated shall be ignored; that is, the
       phrase ``leading character'' refers to the next character that has
       not yet been evaluated.

        1. Leading <colon> characters shall be skipped.

        2. Leading <blank> characters shall be skipped.

        3. If the leading character is a double-quote character, the
           characters up to and including the next non-<backslash>-escaped
           <newline> shall be discarded, and any subsequent characters shall
           be parsed as a separate command.

        4. Leading characters that can be interpreted as addresses shall be
           evaluated; see Addressing in ex.

        5. Leading <blank> characters shall be skipped.

        6. If the next character is a <vertical-line> character or a
           <newline>:

            a. If the next character is a <newline>:

                i.  If ex is in open or visual mode, the current line shall
                    be set to the last address specified, if any.

               ii.  Otherwise, if the last command was terminated by a
                    <vertical-line> character, no action shall be taken; for
                    example, the command "||<newline>" shall execute two
                    implied commands, not three.

               iii. Otherwise, step 6.b. shall apply.

            b. Otherwise, the implied command shall be the print command.
               The last #, p, and l flags specified to any ex command shall
               be remembered and shall apply to this implied command.
               Executing the ex number, print, or list command shall set the
               remembered flags to #, nothing, and l, respectively, plus any
               other flags specified for that execution of the number,
               print, or list command.

               If ex is not currently performing a global or v command, and
               no address or count is specified, the current line shall be
               incremented by 1 before the command is executed. If
               incrementing the current line would result in an address past
               the last line in the edit buffer, the command shall fail, and
               the increment shall not happen.

            c. The <newline> or <vertical-line> character shall be discarded
               and any subsequent characters shall be parsed as a separate
               command.

        7. The command name shall be comprised of the next character (if the
           character is not alphabetic), or the next character and any
           subsequent alphabetic characters (if the character is
           alphabetic), with the following exceptions:

            a. Commands that consist of any prefix of the characters in the
               command name delete, followed immediately by any of the
               characters 'l', 'p', '+', '−', or '#' shall be interpreted as
               a delete command, followed by a <blank>, followed by the
               characters that were not part of the prefix of the delete
               command. The maximum number of characters shall be matched to
               the command name delete; for example, "del" shall not be
               treated as "de" followed by the flag l.

            b. Commands that consist of the character 'k', followed by a
               character that can be used as the name of a mark, shall be
               equivalent to the mark command followed by a <blank>,
               followed by the character that followed the 'k'.

            c. Commands that consist of the character 's', followed by
               characters that could be interpreted as valid options to the
               s command, shall be the equivalent of the s command, without
               any pattern or replacement values, followed by a <blank>,
               followed by the characters after the 's'.

        8. The command name shall be matched against the possible command
           names, and a command name that contains a prefix matching the
           characters specified by the user shall be the executed command.
           In the case of commands where the characters specified by the
           user could be ambiguous, the executed command shall be as
           follows:

                        ┌───┬────────┬┬───┬───────┬┬───┬───────┐
                        │a  append ││n  next  ││t  t     │
                        │c  change ││p  print ││u  undo  │
                        │ch change ││pr print ││un undo  │
                        │e  edit   ││r  read  ││v  v     │
                        │m  move   ││re read  ││w  write │
                        │ma mark   ││s  s     ││   │       │
                        └───┴────────┴┴───┴───────┴┴───┴───────┘
           Implementation extensions with names causing similar ambiguities
           shall not be checked for a match until all possible matches for
           commands specified by POSIX.1‐2008 have been checked.

        9. If the command is a !  command, or if the command is a read
           command followed by zero or more <blank> characters and a !, or
           if the command is a write command followed by one or more <blank>
           characters and a !, the rest of the command shall include all
           characters up to a non-<backslash>-escaped <newline>.  The
           <newline> shall be discarded and any subsequent characters shall
           be parsed as a separate ex command.

       10. Otherwise, if the command is an edit, ex, or next command, or a
           visual command while in open or visual mode, the next part of the
           command shall be parsed as follows:

            a. Any '!'  character immediately following the command shall be
               skipped and be part of the command.

            b. Any leading <blank> characters shall be skipped and be part
               of the command.

            c. If the next character is a '+', characters up to the first
               non-<backslash>-escaped <newline> or non-<backslash>-escaped
               <blank> shall be skipped and be part of the command.

            d. The rest of the command shall be determined by the steps
               specified in paragraph 12.

       11. Otherwise, if the command is a global, open, s, or v command, the
           next part of the command shall be parsed as follows:

            a. Any leading <blank> characters shall be skipped and be part
               of the command.

            b. If the next character is not an alphanumeric, double-quote,
               <newline>, <backslash>, or <vertical-line> character:

                i.  The next character shall be used as a command delimiter.

               ii.  If the command is a global, open, or v command,
                    characters up to the first non-<backslash>-escaped
                    <newline>, or first non-<backslash>-escaped delimiter
                    character, shall be skipped and be part of the command.

               iii. If the command is an s command, characters up to the
                    first non-<backslash>-escaped <newline>, or second
                    non-<backslash>-escaped delimiter character, shall be
                    skipped and be part of the command.

            c. If the command is a global or v command, characters up to the
               first non-<backslash>-escaped <newline> shall be skipped and
               be part of the command.

            d. Otherwise, the rest of the command shall be determined by the
               steps specified in paragraph 12.

       12. Otherwise:

            a. If the command was a map, unmap, abbreviate, or unabbreviate
               command, characters up to the first non-<control>‐V-escaped
               <newline>, <vertical-line>, or double-quote character shall
               be skipped and be part of the command.

            b. Otherwise, characters up to the first non-<backslash>-escaped
               <newline>, <vertical-line>, or double-quote character shall
               be skipped and be part of the command.

            c. If the command was an append, change, or insert command, and
               the step 12.b. ended at a <vertical-line> character, any
               subsequent characters, up to the next non-<backslash>-escaped
               <newline> shall be used as input text to the command.

            d. If the command was ended by a double-quote character, all
               subsequent characters, up to the next non-<backslash>-escaped
               <newline>, shall be discarded.

            e. The terminating <newline> or <vertical-line> character shall
               be discarded and any subsequent characters shall be parsed as
               a separate ex command.

       Command arguments shall be parsed as described by the Synopsis and
       Description of each individual ex command. This parsing shall not be
       <blank>-sensitive, except for the !  argument, which must follow the
       command name without intervening <blank> characters, and where it
       would otherwise be ambiguous. For example, count and flag arguments
       need not be <blank>-separated because "d22p" is not ambiguous, but
       file arguments to the ex next command must be separated by one or
       more <blank> characters. Any <blank> in command arguments for the
       abbreviate, unabbreviate, map, and unmap commands can be <control>‐V-
       escaped, in which case the <blank> shall not be used as an argument
       delimiter. Any <blank> in the command argument for any other command
       can be <backslash>-escaped, in which case that <blank> shall not be
       used as an argument delimiter.

       Within command arguments for the abbreviate, unabbreviate, map, and
       unmap commands, any character can be <control>‐V-escaped.  All such
       escaped characters shall be treated literally and shall have no
       special meaning. Within command arguments for all other ex commands
       that are not regular expressions or replacement strings, any
       character that would otherwise have a special meaning can be
       <backslash>-escaped.  Escaped characters shall be treated literally,
       without special meaning as shell expansion characters or '!', '%',
       and '#' expansion characters. See Regular Expressions in ex and
       Replacement Strings in ex for descriptions of command arguments that
       are regular expressions or replacement strings.

       Non-<backslash>-escaped '%' characters appearing in file arguments to
       any ex command shall be replaced by the current pathname; unescaped
       '#' characters shall be replaced by the alternate pathname. It shall
       be an error if '%' or '#' characters appear unescaped in an argument
       and their corresponding values are not set.

       Non-<backslash>-escaped '!'  characters in the arguments to either
       the ex !  command or the open and visual mode !  command, or in the
       arguments to the ex read command, where the first non-<blank> after
       the command name is a '!'  character, or in the arguments to the ex
       write command where the command name is followed by one or more
       <blank> characters and the first non-<blank> after the command name
       is a '!'  character, shall be replaced with the arguments to the last
       of those three commands as they appeared after all unescaped '%',
       '#', and '!'  characters were replaced. It shall be an error if '!'
       characters appear unescaped in one of these commands and there has
       been no previous execution of one of these commands.

       If an error occurs during the parsing or execution of an ex command:

        *  An informational message to this effect shall be written.
           Execution of the ex command shall stop, and the cursor (for
           example, the current line and column) shall not be further
           modified.

        *  If the ex command resulted from a map expansion, all characters
           from that map expansion shall be discarded, except as otherwise
           specified by the map command.

        *  Otherwise, if the ex command resulted from the processing of an
           EXINIT environment variable, a .exrc file, a :source command, a
           −c option, or a +command specified to an ex edit, ex, next, or
           visual command, no further commands from the source of the
           commands shall be executed.

        *  Otherwise, if the ex command resulted from the execution of a
           buffer or a global or v command, no further commands caused by
           the execution of the buffer or the global or v command shall be
           executed.

        *  Otherwise, if the ex command was not terminated by a <newline>,
           all characters up to and including the next
           non-<backslash>-escaped <newline> shall be discarded.

   Input Editing in ex
       The following symbol is used in this and the following sections to
       specify command actions:

       word      In the POSIX locale, a word consists of a maximal sequence
                 of letters, digits, and underscores, delimited at both ends
                 by characters other than letters, digits, or underscores,
                 or by the beginning or end of a line or the edit buffer.

       When accepting input characters from the user, in either ex command
       mode or ex text input mode, ex shall enable canonical mode input
       processing, as defined in the System Interfaces volume of
       POSIX.1‐2008.

       If in ex text input mode:

        1. If the number edit option is set, ex shall prompt for input using
           the line number that would be assigned to the line if it is
           entered, in the format specified for the ex number command.

        2. If the autoindent edit option is set, ex shall prompt for input
           using autoindent characters, as described by the autoindent edit
           option.  autoindent characters shall follow the line number, if
           any.

       If in ex command mode:

        1. If the prompt edit option is set, input shall be prompted for
           using a single ':' character; otherwise, there shall be no
           prompt.

       The input characters in the following sections shall have the
       following effects on the input line.

   Scroll
       Synopsis:
                     eof

       See the description of the stty eof character in stty(1p).

       If in ex command mode:

              If the eof character is the first character entered on the
              line, the line shall be evaluated as if it contained two
              characters: a <control>‐D and a <newline>.

              Otherwise, the eof character shall have no special meaning.

       If in ex text input mode:

              If the cursor follows an autoindent character, the autoindent
              characters in the line shall be modified so that a part of the
              next text input character will be displayed on the first
              column in the line after the previous shiftwidth edit option
              column boundary, and the user shall be prompted again for
              input for the same line.

              Otherwise, if the cursor follows a '0', which follows an
              autoindent character, and the '0' was the previous text input
              character, the '0' and all autoindent characters in the line
              shall be discarded, and the user shall be prompted again for
              input for the same line.

              Otherwise, if the cursor follows a '^', which follows an
              autoindent character, and the '^' was the previous text input
              character, the '^' and all autoindent characters in the line
              shall be discarded, and the user shall be prompted again for
              input for the same line. In addition, the autoindent level for
              the next input line shall be derived from the same line from
              which the autoindent level for the current input line was
              derived.

              Otherwise, if there are no autoindent or text input characters
              in the line, the eof character shall be discarded.

              Otherwise, the eof character shall have no special meaning.

   <newline>
       Synopsis:
                     <newline>
                     <control>-J

       If in ex command mode:

              Cause the command line to be parsed; <control>‐J shall be
              mapped to the <newline> for this purpose.

       If in ex text input mode:

              Terminate the current line. If there are no characters other
              than autoindent characters on the line, all characters on the
              line shall be discarded.

              Prompt for text input on a new line after the current line. If
              the autoindent edit option is set, an appropriate number of
              autoindent characters shall be added as a prefix to the line
              as described by the ex autoindent edit option.

   <backslash>
       Synopsis:
                     <backslash>

       Allow the entry of a subsequent <newline> or <control>‐J as a literal
       character, removing any special meaning that it may have to the
       editor during text input mode. The <backslash> character shall be
       retained and evaluated when the command line is parsed, or retained
       and included when the input text becomes part of the edit buffer.

   <control>‐V
       Synopsis:
                     <control>-V

       Allow the entry of any subsequent character as a literal character,
       removing any special meaning that it may have to the editor during
       text input mode. The <control>‐V character shall be discarded before
       the command line is parsed or the input text becomes part of the edit
       buffer.

       If the ``literal next'' functionality is performed by the underlying
       system, it is implementation-defined whether a character other than
       <control>‐V performs this function.

   <control>‐W
       Synopsis:
                     <control>-W

       Discard the <control>‐W, and the word previous to it in the input
       line, including any <blank> characters following the word and
       preceding the <control>‐W.  If the ``word erase'' functionality is
       performed by the underlying system, it is implementation-defined
       whether a character other than <control>‐W performs this function.

   Command Descriptions in ex
       The following symbols are used in this section to represent command
       modifiers. Some of these modifiers can be omitted, in which case the
       specified defaults shall be used.

       1addr     A single line address, given in any of the forms described
                 in Addressing in ex; the default shall be the current line
                 ('.'), unless otherwise specified.

                 If the line address is zero, it shall be an error, unless
                 otherwise specified in the following command descriptions.

                 If the edit buffer is empty, and the address is specified
                 with a command other than =, append, insert, open, put,
                 read, or visual, or the address is not zero, it shall be an
                 error.

       2addr     Two addresses specifying an inclusive range of lines. If no
                 addresses are specified, the default for 2addr shall be the
                 current line only (".,."), unless otherwise specified in
                 the following command descriptions. If one address is
                 specified, 2addr shall specify that line only, unless
                 otherwise specified in the following command descriptions.

                 It shall be an error if the first address is greater than
                 the second address.

                 If the edit buffer is empty, and the two addresses are
                 specified with a command other than the !, write, wq, or
                 xit commands, or either address is not zero, it shall be an
                 error.

       count     A positive decimal number. If count is specified, it shall
                 be equivalent to specifying an additional address to the
                 command, unless otherwise specified by the following
                 command descriptions. The additional address shall be equal
                 to the last address specified to the command (either
                 explicitly or by default) plus count−1.

                 If this would result in an address greater than the last
                 line of the edit buffer, it shall be corrected to equal the
                 last line of the edit buffer.

       flags     One or more of the characters '+', '−', '#', 'p', or 'l'
                 (ell). The flag characters can be <blank>-separated, and in
                 any order or combination. The characters '#', 'p', and 'l'
                 shall cause lines to be written in the format specified by
                 the print command with the specified flags.

                 The lines to be written are as follows:

                  1. All edit buffer lines written during the execution of
                     the ex &, ~, list, number, open, print, s, visual, and
                     z commands shall be written as specified by flags.

                  2. After the completion of an ex command with a flag as an
                     argument, the current line shall be written as
                     specified by flags, unless the current line was the
                     last line written by the command.

                 The characters '+' and '−' cause the value of the current
                 line after the execution of the ex command to be adjusted
                 by the offset address as described in Addressing in ex.
                 This adjustment shall occur before the current line is
                 written as described in 2. above.

                 The default for flags shall be none.

       buffer    One of a number of named areas for holding text. The named
                 buffers are specified by the alphanumeric characters of the
                 POSIX locale. There shall also be one ``unnamed'' buffer.
                 When no buffer is specified for editor commands that use a
                 buffer, the unnamed buffer shall be used.  Commands that
                 store text into buffers shall store the text as it was
                 before the command took effect, and shall store text
                 occurring earlier in the file before text occurring later
                 in the file, regardless of how the text region was
                 specified. Commands that store text into buffers shall
                 store the text into the unnamed buffer as well as any
                 specified buffer.

                 In ex commands, buffer names are specified as the name by
                 itself. In open or visual mode commands the name is
                 preceded by a double-quote ('"') character.

                 If the specified buffer name is an uppercase character, and
                 the buffer contents are to be modified, the buffer shall be
                 appended to rather than being overwritten. If the buffer is
                 not being modified, specifying the buffer name in lowercase
                 and uppercase shall have identical results.

                 There shall also be buffers named by the numbers 1 through
                 9. In open and visual mode, if a region of text including
                 characters from more than a single line is being modified
                 by the vi c or d commands, the motion character associated
                 with the c or d commands specifies that the buffer text
                 shall be in line mode, or the commands %, `, /, ?, (, ), N,
                 n, {, or } are used to define a region of text for the c or
                 d commands, the contents of buffers 1 through 8 shall be
                 moved into the buffer named by the next numerically greater
                 value, the contents of buffer 9 shall be discarded, and the
                 region of text shall be copied into buffer 1. This shall be
                 in addition to copying the text into a user-specified
                 buffer or unnamed buffer, or both. Numeric buffers can be
                 specified as a source buffer for open and visual mode
                 commands; however, specifying a numeric buffer as the write
                 target of an open or visual mode command shall have
                 unspecified results.

                 The text of each buffer shall have the characteristic of
                 being in either line or character mode. Appending text to a
                 non-empty buffer shall set the mode to match the
                 characteristic of the text being appended. Appending text
                 to a buffer shall cause the creation of at least one
                 additional line in the buffer. All text stored into buffers
                 by ex commands shall be in line mode. The ex commands that
                 use buffers as the source of text specify individually how
                 buffers of different modes are handled. Each open or visual
                 mode command that uses buffers for any purpose specifies
                 individually the mode of the text stored into the buffer
                 and how buffers of different modes are handled.

       file      Command text used to derive a pathname. The default shall
                 be the current pathname, as defined previously, in which
                 case, if no current pathname has yet been established it
                 shall be an error, except where specifically noted in the
                 individual command descriptions that follow.  If the
                 command text contains any of the characters '~', '{', '[',
                 '*', '?', '$', '"', backquote, single-quote, and
                 <backslash>, it shall be subjected to the process of
                 ``shell expansions'', as described below; if more than a
                 single pathname results and the command expects only one,
                 it shall be an error.

                 The process of shell expansions in the editor shall be done
                 as follows. The ex utility shall pass two arguments to the
                 program named by the shell edit option; the first shall be
                 −c, and the second shall be the string "echo" and the
                 command text as a single argument. The standard output and
                 standard error of that command shall replace the command
                 text.

       !         A character that can be appended to the command name to
                 modify its operation, as detailed in the individual command
                 descriptions. With the exception of the ex read, write, and
                 !  commands, the '!'  character shall only act as a
                 modifier if there are no <blank> characters between it and
                 the command name.

       remembered search direction
                 The vi commands N and n begin searching in a forwards or
                 backwards direction in the edit buffer based on a
                 remembered search direction, which is initially unset, and
                 is set by the ex global, v, s, and tag commands, and the vi
                 / and ?  commands.

   Abbreviate
       Synopsis:
                     ab[breviate][lhs rhs]

       If lhs and rhs are not specified, write the current list of
       abbreviations and do nothing more.

       Implementations may restrict the set of characters accepted in lhs or
       rhs, except that printable characters and <blank> characters shall
       not be restricted. Additional restrictions shall be implementation-
       defined.

       In both lhs and rhs, any character may be escaped with a <control>‐V,
       in which case the character shall not be used to delimit lhs from
       rhs, and the escaping <control>‐V shall be discarded.

       In open and visual text input mode, if a non-word or <ESC> character
       that is not escaped by a <control>‐V character is entered after a
       word character, a check shall be made for a set of characters
       matching lhs, in the text input entered during this command. If it is
       found, the effect shall be as if rhs was entered instead of lhs.

       The set of characters that are checked is defined as follows:

        1. If there are no characters inserted before the word and non-word
           or <ESC> characters that triggered the check, the set of
           characters shall consist of the word character.

        2. If the character inserted before the word and non-word or <ESC>
           characters that triggered the check is a word character, the set
           of characters shall consist of the characters inserted
           immediately before the triggering characters that are word
           characters, plus the triggering word character.

        3. If the character inserted before the word and non-word or <ESC>
           characters that triggered the check is not a word character, the
           set of characters shall consist of the characters that were
           inserted before the triggering characters that are neither
           <blank> characters nor word characters, plus the triggering word
           character.

       It is unspecified whether the lhs argument entered for the ex
       abbreviate and unabbreviate commands is replaced in this fashion.
       Regardless of whether or not the replacement occurs, the effect of
       the command shall be as if the replacement had not occurred.

       Current line: Unchanged.

       Current column: Unchanged.

   Append
       Synopsis:
                     [1addr] a[ppend][!]

       Enter ex text input mode; the input text shall be placed after the
       specified line. If line zero is specified, the text shall be placed
       at the beginning of the edit buffer.

       This command shall be affected by the number and autoindent edit
       options; following the command name with '!'  shall cause the
       autoindent edit option setting to be toggled for the duration of this
       command only.

       Current line: Set to the last input line; if no lines were input, set
       to the specified line, or to the first line of the edit buffer if a
       line of zero was specified, or zero if the edit buffer is empty.

       Current column: Set to non-<blank>.

   Arguments
       Synopsis:
                     ar[gs]

       Write the current argument list, with the current argument-list
       entry, if any, between '[' and ']' characters.

       Current line: Unchanged.

       Current column: Unchanged.

   Change
       Synopsis:
                     [2addr] c[hange][!][count]

       Enter ex text input mode; the input text shall replace the specified
       lines. The specified lines shall be copied into the unnamed buffer,
       which shall become a line mode buffer.

       This command shall be affected by the number and autoindent edit
       options; following the command name with '!'  shall cause the
       autoindent edit option setting to be toggled for the duration of this
       command only.

       Current line: Set to the last input line; if no lines were input, set
       to the line before the first address, or to the first line of the
       edit buffer if there are no lines preceding the first address, or to
       zero if the edit buffer is empty.

       Current column: Set to non-<blank>.

   Change Directory
       Synopsis:
                     chd[ir][!][directory]
                     cd[!][directory]

       Change the current working directory to directory.

       If no directory argument is specified, and the HOME environment
       variable is set to a non-null and non-empty value, directory shall
       default to the value named in the HOME environment variable. If the
       HOME environment variable is empty or is undefined, the default value
       of directory is implementation-defined.

       If no '!'  is appended to the command name, and the edit buffer has
       been modified since the last complete write, and the current pathname
       does not begin with a '/', it shall be an error.

       Current line: Unchanged.

       Current column: Unchanged.

   Copy
       Synopsis:
                     [2addr] co[py] 1addr [flags]
                     [2addr] t 1addr [flags]

       Copy the specified lines after the specified destination line; line
       zero specifies that the lines shall be placed at the beginning of the
       edit buffer.

       Current line: Set to the last line copied.

       Current column: Set to non-<blank>.

   Delete
       Synopsis:
                     [2addr] d[elete][buffer][count][flags]

       Delete the specified lines into a buffer (defaulting to the unnamed
       buffer), which shall become a line-mode buffer.

       Flags can immediately follow the command name; see Command Line
       Parsing in ex.

       Current line: Set to the line following the deleted lines, or to the
       last line in the edit buffer if that line is past the end of the edit
       buffer, or to zero if the edit buffer is empty.

       Current column: Set to non-<blank>.

   Edit
       Synopsis:
                     e[dit][!][+command][file]
                     ex[!][+command][file]

       If no '!'  is appended to the command name, and the edit buffer has
       been modified since the last complete write, it shall be an error.

       If file is specified, replace the current contents of the edit buffer
       with the current contents of file, and set the current pathname to
       file.  If file is not specified, replace the current contents of the
       edit buffer with the current contents of the file named by the
       current pathname. If for any reason the current contents of the file
       cannot be accessed, the edit buffer shall be empty.

       The +command option shall be <blank>-delimited; <blank> characters
       within the +command can be escaped by preceding them with a
       <backslash> character. The +command shall be interpreted as an ex
       command immediately after the contents of the edit buffer have been
       replaced and the current line and column have been set.

       If the edit buffer is empty:

       Current line: Set to 0.

       Current column: Set to 1.

       Otherwise, if executed while in ex command mode or if the +command
       argument is specified:

       Current line: Set to the last line of the edit buffer.

       Current column: Set to non-<blank>.

       Otherwise, if file is omitted or results in the current pathname:

       Current line: Set to the first line of the edit buffer.

       Current column: Set to non-<blank>.

       Otherwise, if file is the same as the last file edited, the line and
       column shall be set as follows; if the file was previously edited,
       the line and column may be set as follows:

       Current line: Set to the last value held when that file was last
       edited. If this value is not a valid line in the new edit buffer, set
       to the first line of the edit buffer.

       Current column: If the current line was set to the last value held
       when the file was last edited, set to the last value held when the
       file was last edited.  Otherwise, or if the last value is not a valid
       column in the new edit buffer, set to non-<blank>.

       Otherwise:

       Current line: Set to the first line of the edit buffer.

       Current column: Set to non-<blank>.

   File
       Synopsis:
                     f[ile][file]

       If a file argument is specified, the alternate pathname shall be set
       to the current pathname, and the current pathname shall be set to
       file.

       Write an informational message. If the file has a current pathname,
       it shall be included in this message; otherwise, the message shall
       indicate that there is no current pathname. If the edit buffer
       contains lines, the current line number and the number of lines in
       the edit buffer shall be included in this message; otherwise, the
       message shall indicate that the edit buffer is empty. If the edit
       buffer has been modified since the last complete write, this fact
       shall be included in this message. If the readonly edit option is
       set, this fact shall be included in this message. The message may
       contain other unspecified information.

       Current line: Unchanged.

       Current column: Unchanged.

   Global
       Synopsis:
                     [2addr] g[lobal] /pattern/ [commands]
                     [2addr] v /pattern/ [commands]

       The optional '!'  character after the global command shall be the
       same as executing the v command.

       If pattern is empty (for example, "//") or not specified, the last
       regular expression used in the editor command shall be used as the
       pattern.  The pattern can be delimited by <slash> characters (shown
       in the Synopsis), as well as any non-alphanumeric or non-<blank>
       other than <backslash>, <vertical-line>, <newline>, or double-quote.

       If no lines are specified, the lines shall default to the entire
       file.

       The global and v commands are logically two-pass operations. First,
       mark the lines within the specified lines for which the line
       excluding the terminating <newline> matches (global) or does not
       match (v or global!)  the specified pattern. Second, execute the ex
       commands given by commands, with the current line ('.')  set to each
       marked line. If an error occurs during this process, or the contents
       of the edit buffer are replaced (for example, by the ex :edit
       command) an error message shall be written and no more commands
       resulting from the execution of this command shall be processed.

       Multiple ex commands can be specified by entering multiple commands
       on a single line using a <vertical-line> to delimit them, or one per
       line, by escaping each <newline> with a <backslash>.

       If no commands are specified:

        1. If in ex command mode, it shall be as if the print command were
           specified.

        2. Otherwise, no command shall be executed.

       For the append, change, and insert commands, the input text shall be
       included as part of the command, and the terminating <period> can be
       omitted if the command ends the list of commands. The open and visual
       commands can be specified as one of the commands, in which case each
       marked line shall cause the editor to enter open or visual mode. If
       open or visual mode is exited using the vi Q command, the current
       line shall be set to the next marked line, and open or visual mode
       reentered, until the list of marked lines is exhausted.

       The global, v, and undo commands cannot be used in commands.  Marked
       lines may be deleted by commands executed for lines occurring earlier
       in the file than the marked lines. In this case, no commands shall be
       executed for the deleted lines.

       If the remembered search direction is not set, the global and v
       commands shall set it to forward.

       The autoprint and autoindent edit options shall be inhibited for the
       duration of the g or v command.

       Current line: If no commands executed, set to the last marked line.
       Otherwise, as specified for the executed ex commands.

       Current column: If no commands are executed, set to non-<blank>;
       otherwise, as specified for the individual ex commands.

   Insert
       Synopsis:
                     [1addr] i[nsert][!]

       Enter ex text input mode; the input text shall be placed before the
       specified line. If the line is zero or 1, the text shall be placed at
       the beginning of the edit buffer.

       This command shall be affected by the number and autoindent edit
       options; following the command name with '!'  shall cause the
       autoindent edit option setting to be toggled for the duration of this
       command only.

       Current line: Set to the last input line; if no lines were input, set
       to the line before the specified line, or to the first line of the
       edit buffer if there are no lines preceding the specified line, or
       zero if the edit buffer is empty.

       Current column: Set to non-<blank>.

   Join
       Synopsis:
                     [2addr] j[oin][!][count][flags]

       If count is specified:

              If no address was specified, the join command shall behave as
              if 2addr were the current line and the current line plus count
              (.,. + count).

              If one address was specified, the join command shall behave as
              if 2addr were the specified address and the specified address
              plus count (addr,addr + count).

              If two addresses were specified, the join command shall behave
              as if an additional address, equal to the last address plus
              count −1 (addr1,addr2,addr2 + count −1), was specified.

              If this would result in a second address greater than the last
              line of the edit buffer, it shall be corrected to be equal to
              the last line of the edit buffer.

       If no count is specified:

              If no address was specified, the join command shall behave as
              if 2addr were the current line and the next line (.,. +1).

              If one address was specified, the join command shall behave as
              if 2addr were the specified address and the next line
              (addr,addr +1).

       Join the text from the specified lines together into a single line,
       which shall replace the specified lines.

       If a '!'  character is appended to the command name, the join shall
       be without modification of any line, independent of the current
       locale.

       Otherwise, in the POSIX locale, set the current line to the first of
       the specified lines, and then, for each subsequent line, proceed as
       follows:

        1. Discard leading <space> characters from the line to be joined.

        2. If the line to be joined is now empty, delete it, and skip steps
           3 through 5.

        3. If the current line ends in a <blank>, or the first character of
           the line to be joined is a ')' character, join the lines without
           further modification.

        4. If the last character of the current line is a '.', join the
           lines with two <space> characters between them.

        5. Otherwise, join the lines with a single <space> between them.

       Current line: Set to the first line specified.

       Current column: Set to non-<blank>.

   List
       Synopsis:
                     [2addr] l[ist][count][flags]

       This command shall be equivalent to the ex command:

           [2addr] p[rint][count] l[flags]

       See Print.

   Map
       Synopsis:
                     map[!][lhs rhs]

       If lhs and rhs are not specified:

        1. If '!'  is specified, write the current list of text input mode
           maps.

        2. Otherwise, write the current list of command mode maps.

        3. Do nothing more.

       Implementations may restrict the set of characters accepted in lhs or
       rhs, except that printable characters and <blank> characters shall
       not be restricted. Additional restrictions shall be implementation-
       defined. In both lhs and rhs, any character can be escaped with a
       <control>‐V, in which case the character shall not be used to delimit
       lhs from rhs, and the escaping <control>‐V shall be discarded.

       If the character '!'  is appended to the map command name, the
       mapping shall be effective during open or visual text input mode
       rather than open or visual command mode. This allows lhs to have two
       different map definitions at the same time: one for command mode and
       one for text input mode.

       For command mode mappings:

              When the lhs is entered as any part of a vi command in open or
              visual mode (but not as part of the arguments to the command),
              the action shall be as if the corresponding rhs had been
              entered.

              If any character in the command, other than the first, is
              escaped using a <control>‐V character, that character shall
              not be part of a match to an lhs.

              It is unspecified whether implementations shall support map
              commands where the lhs is more than a single character in
              length, where the first character of the lhs is printable.

              If lhs contains more than one character and the first
              character is '#', followed by a sequence of digits
              corresponding to a numbered function key, then when this
              function key is typed it shall be mapped to rhs.  Characters
              other than digits following a '#' character also represent the
              function key named by the characters in the lhs following the
              '#' and may be mapped to rhs.  It is unspecified how function
              keys are named or what function keys are supported.

       For text input mode mappings:

              When the lhs is entered as any part of text entered in open or
              visual text input modes, the action shall be as if the
              corresponding rhs had been entered.

              If any character in the input text is escaped using a
              <control>‐V character, that character shall not be part of a
              match to an lhs.

              It is unspecified whether the lhs text entered for subsequent
              map or unmap commands is replaced with the rhs text for the
              purposes of the screen display; regardless of whether or not
              the display appears as if the corresponding rhs text was
              entered, the effect of the command shall be as if the lhs text
              was entered.

       If only part of the lhs is entered, it is unspecified how long the
       editor will wait for additional, possibly matching characters before
       treating the already entered characters as not matching the lhs.

       The rhs characters shall themselves be subject to remapping, unless
       otherwise specified by the remap edit option, except that if the
       characters in lhs occur as prefix characters in rhs, those characters
       shall not be remapped.

       On block-mode terminals, the mapping need not occur immediately (for
       example, it may occur after the terminal transmits a group of
       characters to the system), but it shall achieve the same results as
       if it occurred immediately.

       Current line: Unchanged.

       Current column: Unchanged.

   Mark
       Synopsis:
                     [1addr] ma[rk] character
                     [1addr] k character

       Implementations shall support character values of a single lowercase
       letter of the POSIX locale and the backquote and single-quote
       characters; support of other characters is implementation-defined.

       If executing the vi m command, set the specified mark to the current
       line and 1-based numbered character referenced by the current column,
       if any; otherwise, column position 1.

       Otherwise, set the specified mark to the specified line and 1-based
       numbered first non-<blank> non-<newline> in the line, if any;
       otherwise, the last non-<newline> in the line, if any; otherwise,
       column position 1.

       The mark shall remain associated with the line until the mark is
       reset or the line is deleted. If a deleted line is restored by a
       subsequent undo command, any marks previously associated with the
       line, which have not been reset, shall be restored as well. Any use
       of a mark not associated with a current line in the edit buffer shall
       be an error.

       The marks ` and ' shall be set as described previously, immediately
       before the following events occur in the editor:

        1. The use of '$' as an ex address

        2. The use of a positive decimal number as an ex address

        3. The use of a search command as an ex address

        4. The use of a mark reference as an ex address

        5. The use of the following open and visual mode commands:
           <control>‐], %, (, ), [, ], {, }

        6. The use of the following open and visual mode commands: ', G, H,
           L, M, z if the current line will change as a result of the
           command

        7. The use of the open and visual mode commands: /, ?, N, `, n if
           the current line or column will change as a result of the command

        8. The use of the ex mode commands: z, undo, global, v

       For rules 1., 2., 3., and 4., the ` and ' marks shall not be set if
       the ex command is parsed as specified by rule 6.a. in Command Line
       Parsing in ex.

       For rules 5., 6., and 7., the ` and ' marks shall not be set if the
       commands are used as motion commands in open and visual mode.

       For rules 1., 2., 3., 4., 5., 6., 7., and 8., the ` and ' marks shall
       not be set if the command fails.

       The ` and ' marks shall be set as described previously, each time the
       contents of the edit buffer are replaced (including the editing of
       the initial buffer), if in open or visual mode, or if in ex mode and
       the edit buffer is not empty, before any commands or movements
       (including commands or movements specified by the −c or −t options or
       the +command argument) are executed on the edit buffer. If in open or
       visual mode, the marks shall be set as if executing the vi m command;
       otherwise, as if executing the ex mark command.

       When changing from ex mode to open or visual mode, if the ` and '
       marks are not already set, the ` and ' marks shall be set as
       described previously.

       Current line: Unchanged.

       Current column: Unchanged.

   Move
       Synopsis:
                     [2addr] m[ove] 1addr [flags]

       Move the specified lines after the specified destination line. A
       destination of line zero specifies that the lines shall be placed at
       the beginning of the edit buffer. It shall be an error if the
       destination line is within the range of lines to be moved.

       Current line: Set to the last of the moved lines.

       Current column: Set to non-<blank>.

   Next
       Synopsis:
                     n[ext][!][+command][file ...]

       If no '!'  is appended to the command name, and the edit buffer has
       been modified since the last complete write, it shall be an error,
       unless the file is successfully written as specified by the autowrite
       option.

       If one or more files is specified:

        1. Set the argument list to the specified filenames.

        2. Set the current argument list reference to be the first entry in
           the argument list.

        3. Set the current pathname to the first filename specified.

       Otherwise:

        1. It shall be an error if there are no more filenames in the
           argument list after the filename currently referenced.

        2. Set the current pathname and the current argument list reference
           to the filename after the filename currently referenced in the
           argument list.

       Replace the contents of the edit buffer with the contents of the file
       named by the current pathname. If for any reason the contents of the
       file cannot be accessed, the edit buffer shall be empty.

       This command shall be affected by the autowrite and writeany edit
       options.

       The +command option shall be <blank>-delimited; <blank> characters
       can be escaped by preceding them with a <backslash> character. The
       +command shall be interpreted as an ex command immediately after the
       contents of the edit buffer have been replaced and the current line
       and column have been set.

       Current line: Set as described for the edit command.

       Current column: Set as described for the edit command.

   Number
       Synopsis:
                     [2addr] nu[mber][count][flags]
                     [2addr] #[count][flags]

       These commands shall be equivalent to the ex command:

           [2addr] p[rint][count] #[flags]

       See Print.

   Open
       Synopsis:
                     [1addr] o[pen] /pattern/ [flags]

       This command need not be supported on block-mode terminals or
       terminals with insufficient capabilities. If standard input, standard
       output, or standard error are not terminal devices, the results are
       unspecified.

       Enter open mode.

       The trailing delimiter can be omitted from pattern at the end of the
       command line. If pattern is empty (for example, "//") or not
       specified, the last regular expression used in the editor shall be
       used as the pattern. The pattern can be delimited by <slash>
       characters (shown in the Synopsis), as well as any alphanumeric, or
       non-<blank> other than <backslash>, <vertical-line>, <newline>, or
       double-quote.

       Current line: Set to the specified line.

       Current column: Set to non-<blank>.

   Preserve
       Synopsis:
                     pre[serve]

       Save the edit buffer in a form that can later be recovered by using
       the −r option or by using the ex recover command. After the file has
       been preserved, a mail message shall be sent to the user. This
       message shall be readable by invoking the mailx utility. The message
       shall contain the name of the file, the time of preservation, and an
       ex command that could be used to recover the file. Additional
       information may be included in the mail message.

       Current line: Unchanged.

       Current column: Unchanged.

   Print
       Synopsis:
                     [2addr] p[rint][count][flags]

       Write the addressed lines. The behavior is unspecified if the number
       of columns on the display is less than the number of columns required
       to write any single character in the lines being written.

       Non-printable characters, except for the <tab>, shall be written as
       implementation-defined multi-character sequences.

       If the # flag is specified or the number edit option is set, each
       line shall be preceded by its line number in the following format:

           "%6d  ", <line number>

       If the l flag is specified or the list edit option is set:

        1. The characters listed in the Base Definitions volume of
           POSIX.1‐2008, Table 5-1, Escape Sequences and Associated Actions
           shall be written as the corresponding escape sequence.

        2. Non-printable characters not in the Base Definitions volume of
           POSIX.1‐2008, Table 5-1, Escape Sequences and Associated Actions
           shall be written as one three-digit octal number (with a
           preceding <backslash>) for each byte in the character (most
           significant byte first).

        3. The end of each line shall be marked with a '$', and literal '$'
           characters within the line shall be written with a preceding
           <backslash>.

       Long lines shall be folded; the length at which folding occurs is
       unspecified, but should be appropriate for the output terminal,
       considering the number of columns of the terminal.

       If a line is folded, and the l flag is not specified and the list
       edit option is not set, it is unspecified whether a multi-column
       character at the folding position is separated; it shall not be
       discarded.

       Current line: Set to the last written line.

       Current column: Unchanged if the current line is unchanged;
       otherwise, set to non-<blank>.

   Put
       Synopsis:
                     [1addr] pu[t][buffer]

       Append text from the specified buffer (by default, the unnamed
       buffer) to the specified line; line zero specifies that the text
       shall be placed at the beginning of the edit buffer. Each portion of
       a line in the buffer shall become a new line in the edit buffer,
       regardless of the mode of the buffer.

       Current line: Set to the last line entered into the edit buffer.

       Current column: Set to non-<blank>.

   Quit
       Synopsis:
                     q[uit][!]

       If no '!'  is appended to the command name:

        1. If the edit buffer has been modified since the last complete
           write, it shall be an error.

        2. If there are filenames in the argument list after the filename
           currently referenced, and the last command was not a quit, wq,
           xit, or ZZ (see Exit) command, it shall be an error.

       Otherwise, terminate the editing session.

   Read
       Synopsis:
                     [1addr] r[ead][!][file]

       If '!'  is not the first non-<blank> to follow the command name, a
       copy of the specified file shall be appended into the edit buffer
       after the specified line; line zero specifies that the copy shall be
       placed at the beginning of the edit buffer. The number of lines and
       bytes read shall be written. If no file is named, the current
       pathname shall be the default. If there is no current pathname, then
       file shall become the current pathname. If there is no current
       pathname or file operand, it shall be an error. Specifying a file
       that is not of type regular shall have unspecified results.

       Otherwise, if file is preceded by '!', the rest of the line after the
       '!'  shall have '%', '#', and '!'  characters expanded as described
       in Command Line Parsing in ex.

       The ex utility shall then pass two arguments to the program named by
       the shell edit option; the first shall be −c and the second shall be
       the expanded arguments to the read command as a single argument. The
       standard input of the program shall be set to the standard input of
       the ex program when it was invoked. The standard error and standard
       output of the program shall be appended into the edit buffer after
       the specified line.

       Each line in the copied file or program output (as delimited by
       <newline> characters or the end of the file or output if it is not
       immediately preceded by a <newline>), shall be a separate line in the
       edit buffer. Any occurrences of <carriage-return> and <newline> pairs
       in the output shall be treated as single <newline> characters.

       The special meaning of the '!'  following the read command can be
       overridden by escaping it with a <backslash> character.

       Current line: If no lines are added to the edit buffer, unchanged.
       Otherwise, if in open or visual mode, set to the first line entered
       into the edit buffer. Otherwise, set to the last line entered into
       the edit buffer.

       Current column: Set to non-<blank>.

   Recover
       Synopsis:
                     rec[over][!] file

       If no '!'  is appended to the command name, and the edit buffer has
       been modified since the last complete write, it shall be an error.

       If no file operand is specified, then the current pathname shall be
       used. If there is no current pathname or file operand, it shall be an
       error.

       If no recovery information has previously been saved about file, the
       recover command shall behave identically to the edit command, and an
       informational message to this effect shall be written.

       Otherwise, set the current pathname to file, and replace the current
       contents of the edit buffer with the recovered contents of file.  If
       there are multiple instances of the file to be recovered, the one
       most recently saved shall be recovered, and an informational message
       that there are previous versions of the file that can be recovered
       shall be written. The editor shall behave as if the contents of the
       edit buffer have already been modified.

       Current file: Set as described for the edit command.

       Current column: Set as described for the edit command.

   Rewind
       Synopsis:
                     rew[ind][!]

       If no '!'  is appended to the command name, and the edit buffer has
       been modified since the last complete write, it shall be an error,
       unless the file is successfully written as specified by the autowrite
       option.

       If the argument list is empty, it shall be an error.

       The current argument list reference and the current pathname shall be
       set to the first filename in the argument list.

       Replace the contents of the edit buffer with the contents of the file
       named by the current pathname. If for any reason the contents of the
       file cannot be accessed, the edit buffer shall be empty.

       This command shall be affected by the autowrite and writeany edit
       options.

       Current line: Set as described for the edit command.

       Current column: Set as described for the edit command.

   Set
       Synopsis:
                     se[t][option[=[value]] ...][nooption ...][option? ...][all]

       When no arguments are specified, write the value of the term edit
       option and those options whose values have been changed from the
       default settings; when the argument all is specified, write all of
       the option values.

       Giving an option name followed by the character '?'  shall cause the
       current value of that option to be written. The '?'  can be separated
       from the option name by zero or more <blank> characters. The '?'
       shall be necessary only for Boolean valued options. Boolean options
       can be given values by the form set option to turn them on or set
       nooption to turn them off; string and numeric options can be assigned
       by the form set option=value.  Any <blank> characters in strings can
       be included as is by preceding each <blank> with an escaping
       <backslash>.  More than one option can be set or listed by a single
       set command by specifying multiple arguments, each separated from the
       next by one or more <blank> characters.

       See Edit Options in ex for details about specific options.

       Current line: Unchanged.

       Current column: Unchanged.

   Shell
       Synopsis:
                     sh[ell]

       Invoke the program named in the shell edit option with the single
       argument −i (interactive mode). Editing shall be resumed when the
       program exits.

       Current line: Unchanged.

       Current column: Unchanged.

   Source
       Synopsis:
                     so[urce] file

       Read and execute ex commands from file.  Lines in the file that are
       blank lines shall be ignored.

       Current line: As specified for the individual ex commands.

       Current column: As specified for the individual ex commands.

   Substitute
       Synopsis:
                     [2addr] s[ubstitute][/pattern/repl/[options][count][flags]]
                     [2addr] &[options][count][flags]]
                     [2addr] ~[options][count][flags]]

       Replace the first instance of the pattern pattern by the string repl
       on each specified line. (See Regular Expressions in ex and
       Replacement Strings in ex.)  Any non-alphabetic, non-<blank>
       delimiter other than <backslash>, '|', <newline>, or double-quote can
       be used instead of '/'.  <backslash> characters can be used to escape
       delimiters, <backslash> characters, and other special characters.

       The trailing delimiter can be omitted from pattern or from repl at
       the end of the command line. If both pattern and repl are not
       specified or are empty (for example, "//"), the last s command shall
       be repeated. If only pattern is not specified or is empty, the last
       regular expression used in the editor shall be used as the pattern.
       If only repl is not specified or is empty, the pattern shall be
       replaced by nothing.  If the entire replacement pattern is '%', the
       last replacement pattern to an s command shall be used.

       Entering a <carriage-return> in repl (which requires an escaping
       <backslash> in ex mode and an escaping <control>‐V in open or vi
       mode) shall split the line at that point, creating a new line in the
       edit buffer. The <carriage-return> shall be discarded.

       If options includes the letter 'g' (global), all non-overlapping
       instances of the pattern in the line shall be replaced.

       If options includes the letter 'c' (confirm), then before each
       substitution the line shall be written; the written line shall
       reflect all previous substitutions. On the following line, <space>
       characters shall be written beneath the characters from the line that
       are before the pattern to be replaced, and '^' characters written
       beneath the characters included in the pattern to be replaced. The ex
       utility shall then wait for a response from the user. An affirmative
       response shall cause the substitution to be done, while any other
       input shall not make the substitution. An affirmative response shall
       consist of a line with the affirmative response (as defined by the
       current locale) at the beginning of the line. This line shall be
       subject to editing in the same way as the ex command line.

       If interrupted (see the ASYNCHRONOUS EVENTS section), any
       modifications confirmed by the user shall be preserved in the edit
       buffer after the interrupt.

       If the remembered search direction is not set, the s command shall
       set it to forward.

       In the second Synopsis, the & command shall repeat the previous
       substitution, as if the & command were replaced by:

           s/pattern/repl/

       where pattern and repl are as specified in the previous s, &, or ~
       command.

       In the third Synopsis, the ~ command shall repeat the previous
       substitution, as if the '~' were replaced by:

           s/pattern/repl/

       where pattern shall be the last regular expression specified to the
       editor, and repl shall be from the previous substitution (including &
       and ~) command.

       These commands shall be affected by the LC_MESSAGES environment
       variable.

       Current line: Set to the last line in which a substitution occurred,
       or, unchanged if no substitution occurred.

       Current column: Set to non-<blank>.

   Suspend
       Synopsis:
                     su[spend][!]
                     st[op][!]

       Allow control to return to the invoking process; ex shall suspend
       itself as if it had received the SIGTSTP signal. The suspension shall
       occur only if job control is enabled in the invoking shell (see the
       description of set −m).

       These commands shall be affected by the autowrite and writeany edit
       options.

       The current susp character (see stty(1p)) shall be equivalent to the
       suspend command.

   Tag
       Synopsis:
                     ta[g][!] tagstring

       The results are unspecified if the format of a tags file is not as
       specified by the ctags utility (see ctags(1p)) description.

       The tag command shall search for tagstring in the tag files referred
       to by the tag edit option, in the order they are specified, until a
       reference to tagstring is found. Files shall be searched from
       beginning to end. If no reference is found, it shall be an error and
       an error message to this effect shall be written. If the reference is
       not found, or if an error occurs while processing a file referred to
       in the tag edit option, it shall be an error, and an error message
       shall be written at the first occurrence of such an error.

       Otherwise, if the tags file contained a pattern, the pattern shall be
       treated as a regular expression used in the editor; for example, for
       the purposes of the s command.

       If the tagstring is in a file with a different name than the current
       pathname, set the current pathname to the name of that file, and
       replace the contents of the edit buffer with the contents of that
       file. In this case, if no '!'  is appended to the command name, and
       the edit buffer has been modified since the last complete write, it
       shall be an error, unless the file is successfully written as
       specified by the autowrite option.

       This command shall be affected by the autowrite, tag, taglength, and
       writeany edit options.

       Current line: If the tags file contained a line number, set to that
       line number. If the line number is larger than the last line in the
       edit buffer, an error message shall be written and the current line
       shall be set as specified for the edit command.

       If the tags file contained a pattern, set to the first occurrence of
       the pattern in the file. If no matching pattern is found, an error
       message shall be written and the current line shall be set as
       specified for the edit command.

       Current column: If the tags file contained a line-number reference
       and that line-number was not larger than the last line in the edit
       buffer, or if the tags file contained a pattern and that pattern was
       found, set to non-<blank>.  Otherwise, set as specified for the edit
       command.

   Unabbreviate
       Synopsis:
                     una[bbrev] lhs

       If lhs is not an entry in the current list of abbreviations (see
       Abbreviate), it shall be an error. Otherwise, delete lhs from the
       list of abbreviations.

       Current line: Unchanged.

       Current column: Unchanged.

   Undo
       Synopsis:
                     u[ndo]

       Reverse the changes made by the last command that modified the
       contents of the edit buffer, including undo.  For this purpose, the
       global, v, open, and visual commands, and commands resulting from
       buffer executions and mapped character expansions, are considered
       single commands.

       If no action that can be undone preceded the undo command, it shall
       be an error.

       If the undo command restores lines that were marked, the mark shall
       also be restored unless it was reset subsequent to the deletion of
       the lines.

       Current line:

        1. If lines are added or changed in the file, set to the first line
           added or changed.

        2. Set to the line before the first line deleted, if it exists.

        3. Set to 1 if the edit buffer is not empty.

        4. Set to zero.

       Current column: Set to non-<blank>.

   Unmap
       Synopsis:
                     unm[ap][!] lhs

       If '!'  is appended to the command name, and if lhs is not an entry
       in the list of text input mode map definitions, it shall be an error.
       Otherwise, delete lhs from the list of text input mode map
       definitions.

       If no '!'  is appended to the command name, and if lhs is not an
       entry in the list of command mode map definitions, it shall be an
       error. Otherwise, delete lhs from the list of command mode map
       definitions.

       Current line: Unchanged.

       Current column: Unchanged.

   Version
       Synopsis:
                     ve[rsion]

       Write a message containing version information for the editor. The
       format of the message is unspecified.

       Current line: Unchanged.

       Current column: Unchanged.

   Visual
       Synopsis:
                     [1addr] vi[sual][type][count][flags]

       If ex is currently in open or visual mode, the Synopsis and behavior
       of the visual command shall be the same as the edit command, as
       specified by Edit.

       Otherwise, this command need not be supported on block-mode terminals
       or terminals with insufficient capabilities. If standard input,
       standard output, or standard error are not terminal devices, the
       results are unspecified.

       If count is specified, the value of the window edit option shall be
       set to count (as described in window).  If the '^' type character was
       also specified, the window edit option shall be set before being used
       by the type character.

       Enter visual mode. If type is not specified, it shall be as if a type
       of '+' was specified. The type shall cause the following effects:

       +     Place the beginning of the specified line at the top of the
             display.

       -     Place the end of the specified line at the bottom of the
             display.

       .     Place the beginning of the specified line in the middle of the
             display.

       ^     If the specified line is less than or equal to the value of the
             window edit option, set the line to 1; otherwise, decrement the
             line by the value of the window edit option minus 1. Place the
             beginning of this line as close to the bottom of the displayed
             lines as possible, while still displaying the value of the
             window edit option number of lines.

       Current line: Set to the specified line.

       Current column: Set to non-<blank>.

   Write
       Synopsis:
                     [2addr] w[rite][!][>>][file]
                     [2addr] w[rite][!][file]
                     [2addr] wq[!][>>][file]

       If no lines are specified, the lines shall default to the entire
       file.

       The command wq shall be equivalent to a write command followed by a
       quit command; wq!  shall be equivalent to write!  followed by quit.
       In both cases, if the write command fails, the quit shall not be
       attempted.

       If the command name is not followed by one or more <blank>
       characters, or file is not preceded by a '!'  character, the write
       shall be to a file.

        1. If the >> argument is specified, and the file already exists, the
           lines shall be appended to the file instead of replacing its
           contents. If the >> argument is specified, and the file does not
           already exist, it is unspecified whether the write shall proceed
           as if the >> argument had not been specified or if the write
           shall fail.

        2. If the readonly edit option is set (see readonly), the write
           shall fail.

        3. If file is specified, and is not the current pathname, and the
           file exists, the write shall fail.

        4. If file is not specified, the current pathname shall be used. If
           there is no current pathname, the write command shall fail.

        5. If the current pathname is used, and the current pathname has
           been changed by the file or read commands, and the file exists,
           the write shall fail. If the write is successful, subsequent
           writes shall not fail for this reason (unless the current
           pathname is changed again).

        6. If the whole edit buffer is not being written, and the file to be
           written exists, the write shall fail.

       For rules 1., 2., 3., and 5., the write can be forced by appending
       the character '!'  to the command name.

       For rules 2., 3., and 5., the write can be forced by setting the
       writeany edit option.

       Additional, implementation-defined tests may cause the write to fail.

       If the edit buffer is empty, a file without any contents shall be
       written.

       An informational message shall be written noting the number of lines
       and bytes written.

       Otherwise, if the command is followed by one or more <blank>
       characters, and the file is preceded by '!', the rest of the line
       after the '!'  shall have '%', '#', and '!'  characters expanded as
       described in Command Line Parsing in ex.

       The ex utility shall then pass two arguments to the program named by
       the shell edit option; the first shall be −c and the second shall be
       the expanded arguments to the write command as a single argument. The
       specified lines shall be written to the standard input of the
       command. The standard error and standard output of the program, if
       any, shall be written as described for the print command. If the last
       character in that output is not a <newline>, a <newline> shall be
       written at the end of the output.

       The special meaning of the '!'  following the write command can be
       overridden by escaping it with a <backslash> character.

       Current line: Unchanged.

       Current column: Unchanged.

   Write and Exit
       Synopsis:
                     [2addr] x[it][!][file]

       If the edit buffer has not been modified since the last complete
       write, xit shall be equivalent to the quit command, or if a '!'  is
       appended to the command name, to quit!.

       Otherwise, xit shall be equivalent to the wq command, or if a '!'  is
       appended to the command name, to wq!.

       Current line: Unchanged.

       Current column: Unchanged.

   Yank
       Synopsis:
                     [2addr] ya[nk][buffer][count]

       Copy the specified lines to the specified buffer (by default, the
       unnamed buffer), which shall become a line-mode buffer.

       Current line: Unchanged.

       Current column: Unchanged.

   Adjust Window
       Synopsis:
                     [1addr] z[!][type ...][count][flags]

       If no line is specified, the current line shall be the default; if
       type is omitted as well, the current line value shall first be
       incremented by 1. If incrementing the current line would cause it to
       be greater than the last line in the edit buffer, it shall be an
       error.

       If there are <blank> characters between the type argument and the
       preceding z command name or optional '!'  character, it shall be an
       error.

       If count is specified, the value of the window edit option shall be
       set to count (as described in window).  If count is omitted, it shall
       default to 2 times the value of the scroll edit option, or if !  was
       specified, the number of lines in the display minus 1.

       If type is omitted, then count lines starting with the specified line
       shall be written. Otherwise, count lines starting with the line
       specified by the type argument shall be written.

       The type argument shall change the lines to be written. The possible
       values of type are as follows:

       −     The specified line shall be decremented by the following value:

                 (((number of ``−'' characters) x count) −1)

             If the calculation would result in a number less than 1, it
             shall be an error. Write lines from the edit buffer, starting
             at the new value of line, until count lines or the last line in
             the edit buffer has been written.

       +     The specified line shall be incremented by the following value:

                 (((number of ``+'' characters) −1) x count) +1

             If the calculation would result in a number greater than the
             last line in the edit buffer, it shall be an error. Write lines
             from the edit buffer, starting at the new value of line, until
             count lines or the last line in the edit buffer has been
             written.

       =,.   If more than a single '.'  or '=' is specified, it shall be an
             error. The following steps shall be taken:

              1. If count is zero, nothing shall be written.

              2. Write as many of the N lines before the current line in the
                 edit buffer as exist. If count or '!'  was specified, N
                 shall be:

                     (count −1) /2

                 Otherwise, N shall be:

                     (count −3) /2

                 If N is a number less than 3, no lines shall be written.

              3. If '=' was specified as the type character, write a line
                 consisting of the smaller of the number of columns in the
                 display divided by two, or 40 '−' characters.

              4. Write the current line.

              5. Repeat step 3.

              6. Write as many of the N lines after the current line in the
                 edit buffer as exist.  N shall be defined as in step 2. If
                 N is a number less than 3, no lines shall be written. If
                 count is less than 3, no lines shall be written.

       ^     The specified line shall be decremented by the following value:

                 (((number of ``^'' characters) +1) x count) −1

             If the calculation would result in a number less than 1, it
             shall be an error. Write lines from the edit buffer, starting
             at the new value of line, until count lines or the last line in
             the edit buffer has been written.

       Current line: Set to the last line written, unless the type is =, in
       which case, set to the specified line.

       Current column: Set to non-<blank>.

   Escape
       Synopsis:
                     ! command
                     [addr]! command

       The contents of the line after the '!'  shall have '%', '#', and '!'
       characters expanded as described in Command Line Parsing in ex.  If
       the expansion causes the text of the line to change, it shall be
       redisplayed, preceded by a single '!'  character.

       The ex utility shall execute the program named by the shell edit
       option. It shall pass two arguments to the program; the first shall
       be −c, and the second shall be the expanded arguments to the !
       command as a single argument.

       If no lines are specified, the standard input, standard output, and
       standard error of the program shall be set to the standard input,
       standard output, and standard error of the ex program when it was
       invoked. In addition, a warning message shall be written if the edit
       buffer has been modified since the last complete write, and the warn
       edit option is set.

       If lines are specified, they shall be passed to the program as
       standard input, and the standard output and standard error of the
       program shall replace those lines in the edit buffer. Each line in
       the program output (as delimited by <newline> characters or the end
       of the output if it is not immediately preceded by a <newline>),
       shall be a separate line in the edit buffer. Any occurrences of
       <carriage-return> and <newline> pairs in the output shall be treated
       as single <newline> characters. The specified lines shall be copied
       into the unnamed buffer before they are replaced, and the unnamed
       buffer shall become a line-mode buffer.

       If in ex mode, a single '!'  character shall be written when the
       program completes.

       This command shall be affected by the shell and warn edit options. If
       no lines are specified, this command shall be affected by the
       autowrite and writeany edit options. If lines are specified, this
       command shall be affected by the autoprint edit option.

       Current line:

        1. If no lines are specified, unchanged.

        2. Otherwise, set to the last line read in, if any lines are read
           in.

        3. Otherwise, set to the line before the first line of the lines
           specified, if that line exists.

        4. Otherwise, set to the first line of the edit buffer if the edit
           buffer is not empty.

        5. Otherwise, set to zero.

       Current column: If no lines are specified, unchanged. Otherwise, set
       to non-<blank>.

   Shift Left
       Synopsis:
                     [2addr] <[< ...][count][flags]

       Shift the specified lines to the start of the line; the number of
       column positions to be shifted shall be the number of command
       characters times the value of the shiftwidth edit option. Only
       leading <blank> characters shall be deleted or changed into other
       <blank> characters in shifting; other characters shall not be
       affected.

       Lines to be shifted shall be copied into the unnamed buffer, which
       shall become a line-mode buffer.

       This command shall be affected by the autoprint edit option.

       Current line: Set to the last line in the lines specified.

       Current column: Set to non-<blank>.

   Shift Right
       Synopsis:
                     [2addr] >[> ...][count][flags]

       Shift the specified lines away from the start of the line; the number
       of column positions to be shifted shall be the number of command
       characters times the value of the shiftwidth edit option. The shift
       shall be accomplished by adding <blank> characters as a prefix to the
       line or changing leading <blank> characters into other <blank>
       characters. Empty lines shall not be changed.

       Lines to be shifted shall be copied into the unnamed buffer, which
       shall become a line-mode buffer.

       This command shall be affected by the autoprint edit option.

       Current line: Set to the last line in the lines specified.

       Current column: Set to non-<blank>.

   <control>‐D
       Synopsis:
                     <control>-D

       Write the next n lines, where n is the minimum of the values of the
       scroll edit option and the number of lines after the current line in
       the edit buffer. If the current line is the last line of the edit
       buffer it shall be an error.

       Current line: Set to the last line written.

       Current column: Set to non-<blank>.

   Write Line Number
       Synopsis:
                     [1addr] = [flags]

       If line is not specified, it shall default to the last line in the
       edit buffer.  Write the line number of the specified line.

       Current line: Unchanged.

       Current column: Unchanged.

   Execute
       Synopsis:
                     [2addr] @ buffer
                     [2addr] * buffer

       If no buffer is specified or is specified as '@' or '*', the last
       buffer executed shall be used. If no previous buffer has been
       executed, it shall be an error.

       For each line specified by the addresses, set the current line ('.')
       to the specified line, and execute the contents of the named buffer
       (as they were at the time the @ command was executed) as ex commands.
       For each line of a line-mode buffer, and all but the last line of a
       character-mode buffer, the ex command parser shall behave as if the
       line was terminated by a <newline>.

       If an error occurs during this process, or a line specified by the
       addresses does not exist when the current line would be set to it, or
       more than a single line was specified by the addresses, and the
       contents of the edit buffer are replaced (for example, by the ex
       :edit command) an error message shall be written, and no more
       commands resulting from the execution of this command shall be
       processed.

       Current line: As specified for the individual ex commands.

       Current column: As specified for the individual ex commands.

   Regular Expressions in ex
       The ex utility shall support regular expressions that are a superset
       of the basic regular expressions described in the Base Definitions
       volume of POSIX.1‐2008, Section 9.3, Basic Regular Expressions.  A
       null regular expression ("//") shall be equivalent to the last
       regular expression encountered.

       Regular expressions can be used in addresses to specify lines and, in
       some commands (for example, the substitute command), to specify
       portions of a line to be substituted.

       The following constructs can be used to enhance the basic regular
       expressions:

       \<    Match the beginning of a word.  (See the definition of word at
             the beginning of Command Descriptions in ex.)

       \>    Match the end of a word.

       ~     Match the replacement part of the last substitute command. The
             <tilde> ('~') character can be escaped in a regular expression
             to become a normal character with no special meaning. The
             <backslash> shall be discarded.

       When the editor option magic is not set, the only characters with
       special meanings shall be '^' at the beginning of a pattern, '$' at
       the end of a pattern, and <backslash>.  The characters '.', '*', '[',
       and '~' shall be treated as ordinary characters unless preceded by a
       <backslash>; when preceded by a <backslash> they shall regain their
       special meaning, or in the case of <backslash>, be handled as a
       single <backslash>.  <backslash> characters used to escape other
       characters shall be discarded.

   Replacement Strings in ex
       The character '&' ('\&' if the editor option magic is not set) in the
       replacement string shall stand for the text matched by the pattern to
       be replaced. The character '~' ('\~' if magic is not set) shall be
       replaced by the replacement part of the previous substitute command.
       The sequence '\n', where n is an integer, shall be replaced by the
       text matched by the corresponding back-reference expression. If the
       corresponding back-reference expression does not match, then the
       characters '\n' shall be replaced by the empty string.

       The strings '\l', '\u', '\L', and '\U' can be used to modify the case
       of elements in the replacement string (using the '\&' or "\"digit)
       notation. The string '\l' ('\u') shall cause the character that
       follows to be converted to lowercase (uppercase). The string '\L'
       ('\U') shall cause all characters subsequent to it to be converted to
       lowercase (uppercase) as they are inserted by the substitution until
       the string '\e' or '\E', or the end of the replacement string, is
       encountered.

       Otherwise, any character following a <backslash> shall be treated as
       that literal character, and the escaping <backslash> shall be
       discarded.

       An example of case conversion with the s command is as follows:

           :p
           The cat sat on the mat.
           :s/\<.at\>/\u&/gp
           The Cat Sat on the Mat.
           :s/S\(.*\)M/S\U\1\eM/p
           The Cat SAT ON THE Mat.

   Edit Options in ex
       The ex utility has a number of options that modify its behavior.
       These options have default settings, which can be changed using the
       set command.

       Options are Boolean unless otherwise specified.

   autoindent, ai
       [Default unset]

       If autoindent is set, each line in input mode shall be indented
       (using first as many <tab> characters as possible, as determined by
       the editor option tabstop, and then using <space> characters) to
       align with another line, as follows:

        1. If in open or visual mode and the text input is part of a line-
           oriented command (see the EXTENDED DESCRIPTION in vi(1p)), align
           to the first column.

        2. Otherwise, if in open or visual mode, indentation for each line
           shall be set as follows:

            a. If a line was previously inserted as part of this command, it
               shall be set to the indentation of the last inserted line by
               default, or as otherwise specified for the <control>‐D
               character in Input Mode Commands in vi.

            b. Otherwise, it shall be set to the indentation of the previous
               current line, if any; otherwise, to the first column.

        3. For the ex a, i, and c commands, indentation for each line shall
           be set as follows:

            a. If a line was previously inserted as part of this command, it
               shall be set to the indentation of the last inserted line by
               default, or as otherwise specified for the eof character in
               Scroll.

            b. Otherwise, if the command is the ex a command, it shall be
               set to the line appended after, if any; otherwise to the
               first column.

            c. Otherwise, if the command is the ex i command, it shall be
               set to the line inserted before, if any; otherwise to the
               first column.

            d. Otherwise, if the command is the ex c command, it shall be
               set to the indentation of the line replaced.

   autoprint, ap
       [Default set]

       If autoprint is set, the current line shall be written after each ex
       command that modifies the contents of the current edit buffer, and
       after each tag command for which the tag search pattern was found or
       tag line number was valid, unless:

        1. The command was executed while in open or visual mode.

        2. The command was executed as part of a global or v command or @
           buffer execution.

        3. The command was the form of the read command that reads a file
           into the edit buffer.

        4. The command was the append, change, or insert command.

        5. The command was not terminated by a <newline>.

        6. The current line shall be written by a flag specified to the
           command; for example, delete # shall write the current line as
           specified for the flag modifier to the delete command, and not as
           specified by the autoprint edit option.

   autowrite, aw
       [Default unset]

       If autowrite is set, and the edit buffer has been modified since it
       was last completely written to any file, the contents of the edit
       buffer shall be written as if the ex write command had been specified
       without arguments, before each command affected by the autowrite edit
       option is executed. Appending the character '!'  to the command name
       of any of the ex commands except '!'  shall prevent the write. If the
       write fails, it shall be an error and the command shall not be
       executed.

   beautify, bf
       [Default unset]

       If beautify is set, all non-printable characters, other than <tab>,
       <newline>, and <form-feed> characters, shall be discarded from text
       read in from files.

   directory, dir
       [Default implementation-defined]

       The value of this option specifies the directory in which the editor
       buffer is to be placed. If this directory is not writable by the
       user, the editor shall quit.

   edcompatible, ed
       [Default unset]

       Causes the presence of g and c suffixes on substitute commands to be
       remembered, and toggled by repeating the suffixes.

   errorbells, eb
       [Default unset]

       If the editor is in ex mode, and the terminal does not support a
       standout mode (such as inverse video), and errorbells is set, error
       messages shall be preceded by alerting the terminal.

   exrc
       [Default unset]

       If exrc is set, ex shall access any .exrc file in the current
       directory, as described in Initialization in ex and vi.  If exrc is
       not set, ex shall ignore any .exrc file in the current directory
       during initialization, unless the current directory is that named by
       the HOME environment variable.

   ignorecase, ic
       [Default unset]

       If ignorecase is set, characters that have uppercase and lowercase
       representations shall have those representations considered as
       equivalent for purposes of regular expression comparison.

       The ignorecase edit option shall affect all remembered regular
       expressions; for example, unsetting the ignorecase edit option shall
       cause a subsequent vi n command to search for the last basic regular
       expression in a case-sensitive fashion.

   list
       [Default unset]

       If list is set, edit buffer lines written while in ex command mode
       shall be written as specified for the print command with the l flag
       specified. In open or visual mode, each edit buffer line shall be
       displayed as specified for the ex print command with the l flag
       specified. In open or visual text input mode, when the cursor does
       not rest on any character in the line, it shall rest on the '$'
       marking the end of the line.

   magic
       [Default set]

       If magic is set, modify the interpretation of characters in regular
       expressions and substitution replacement strings (see Regular
       Expressions in ex and Replacement Strings in ex).

   mesg
       [Default set]

       If mesg is set, the permission for others to use the write or talk
       commands to write to the terminal shall be turned on while in open or
       visual mode. The shell-level command mesg n shall take precedence
       over any setting of the ex mesg option; that is, if mesg y was issued
       before the editor started (or in a shell escape), such as:

           :!mesg y

       the mesg option in ex shall suppress incoming messages, but the mesg
       option shall not enable incoming messages if mesg n was issued.

   number, nu
       [Default unset]

       If number is set, edit buffer lines written while in ex command mode
       shall be written with line numbers, in the format specified by the
       print command with the # flag specified. In ex text input mode, each
       line shall be preceded by the line number it will have in the file.

       In open or visual mode, each edit buffer line shall be displayed with
       a preceding line number, in the format specified by the ex print
       command with the # flag specified. This line number shall not be
       considered part of the line for the purposes of evaluating the
       current column; that is, column position 1 shall be the first column
       position after the format specified by the print command.

   paragraphs, para
       [Default in the POSIX locale IPLPPPQPP LIpplpipbp]

       The paragraphs edit option shall define additional paragraph
       boundaries for the open and visual mode commands. The paragraphs edit
       option can be set to a character string consisting of zero or more
       character pairs. It shall be an error to set it to an odd number of
       characters.

   prompt
       [Default set]

       If prompt is set, ex command mode input shall be prompted for with a
       <colon> (':'); when unset, no prompt shall be written.

   readonly
       [Default see text]

       If the readonly edit option is set, read-only mode shall be enabled
       (see Write).  The readonly edit option shall be initialized to set if
       either of the following conditions are true:

        *  The command-line option −R was specified.

        *  Performing actions equivalent to the access() function called
           with the following arguments indicates that the file lacks write
           permission:

            1. The current pathname is used as the path argument.

            2. The constant W_OK is used as the amode argument.

       The readonly edit option may be initialized to set for other,
       implementation-defined reasons. The readonly edit option shall not be
       initialized to unset based on any special privileges of the user or
       process. The readonly edit option shall be reinitialized each time
       that the contents of the edit buffer are replaced (for example, by an
       edit or next command) unless the user has explicitly set it, in which
       case it shall remain set until the user explicitly unsets it. Once
       unset, it shall again be reinitialized each time that the contents of
       the edit buffer are replaced.

   redraw
       [Default unset]

       The editor simulates an intelligent terminal on a dumb terminal.
       (Since this is likely to require a large amount of output to the
       terminal, it is useful only at high transmission speeds.)

   remap
       [Default set]

       If remap is set, map translation shall allow for maps defined in
       terms of other maps; translation shall continue until a final product
       is obtained. If unset, only a one-step translation shall be done.

   report
       [Default 5]

       The value of this report edit option specifies what number of lines
       being added, copied, deleted, or modified in the edit buffer will
       cause an informational message to be written to the user. The
       following conditions shall cause an informational message. The
       message shall contain the number of lines added, copied, deleted, or
       modified, but is otherwise unspecified.

        *  An ex or vi editor command, other than open, undo, or visual,
           that modifies at least the value of the report edit option number
           of lines, and which is not part of an ex global or v command, or
           ex or vi buffer execution, shall cause an informational message
           to be written.

        *  An ex yank or vi y or Y command, that copies at least the value
           of the report edit option plus 1 number of lines, and which is
           not part of an ex global or v command, or ex or vi buffer
           execution, shall cause an informational message to be written.

        *  An ex global, v, open, undo, or visual command or ex or vi buffer
           execution, that adds or deletes a total of at least the value of
           the report edit option number of lines, and which is not part of
           an ex global or v command, or ex or vi buffer execution, shall
           cause an informational message to be written.  (For example, if 3
           lines were added and 8 lines deleted during an ex visual command,
           5 would be the number compared against the report edit option
           after the command completed.)

   scroll, scr
       [Default (number of lines in the display −1)/2]

       The value of the scroll edit option shall determine the number of
       lines scrolled by the ex <control>‐D and z commands. For the vi
       <control>‐D and <control>‐U commands, it shall be the initial number
       of lines to scroll when no previous <control>‐D or <control>‐U
       command has been executed.

   sections
       [Default in the POSIX locale NHSHH HUnhsh]

       The sections edit option shall define additional section boundaries
       for the open and visual mode commands. The sections edit option can
       be set to a character string consisting of zero or more character
       pairs; it shall be an error to set it to an odd number of characters.

   shell, sh
       [Default from the environment variable SHELL]

       The value of this option shall be a string. The default shall be
       taken from the SHELL environment variable. If the SHELL environment
       variable is null or empty, the sh (see sh(1p)) utility shall be the
       default.

   shiftwidth, sw
       [Default 8]

       The value of this option shall give the width in columns of an
       indentation level used during autoindentation and by the shift
       commands (< and >).

   showmatch, sm
       [Default unset]

       The functionality described for the showmatch edit option need not be
       supported on block-mode terminals or terminals with insufficient
       capabilities.

       If showmatch is set, in open or visual mode, when a ')' or '}' is
       typed, if the matching '(' or '{' is currently visible on the
       display, the matching '(' or '{' shall be flagged moving the cursor
       to its location for an unspecified amount of time.

   showmode
       [Default unset]

       If showmode is set, in open or visual mode, the current mode that the
       editor is in shall be displayed on the last line of the display.
       Command mode and text input mode shall be differentiated; other
       unspecified modes and implementation-defined information may be
       displayed.

   slowopen
       [Default unset]

       If slowopen is set during open and visual text input modes, the
       editor shall not update portions of the display other than those
       display line columns that display the characters entered by the user
       (see Input Mode Commands in vi).

   tabstop, ts
       [Default 8]

       The value of this edit option shall specify the column boundary used
       by a <tab> in the display (see autoprint, ap and Input Mode Commands
       in vi).

   taglength, tl
       [Default zero]

       The value of this edit option shall specify the maximum number of
       characters that are considered significant in the user-specified tag
       name and in the tag name from the tags file. If the value is zero,
       all characters in both tag names shall be significant.

   tags
       [Default see text]

       The value of this edit option shall be a string of <blank>-delimited
       pathnames of files used by the tag command. The default value is
       unspecified.

   term
       [Default from the environment variable TERM]

       The value of this edit option shall be a string. The default shall be
       taken from the TERM variable in the environment. If the TERM
       environment variable is empty or null, the default is unspecified.
       The editor shall use the value of this edit option to determine the
       type of the display device.

       The results are unspecified if the user changes the value of the term
       edit option after editor initialization.

   terse
       [Default unset]

       If terse is set, error messages may be less verbose. However, except
       for this caveat, error messages are unspecified. Furthermore, not all
       error messages need change for different settings of this option.

   warn
       [Default set]

       If warn is set, and the contents of the edit buffer have been
       modified since they were last completely written, the editor shall
       write a warning message before certain !  commands (see Escape).

   window
       [Default see text]

       A value used in open and visual mode, by the <control>‐B and
       <control>‐F commands, and, in visual mode, to specify the number of
       lines displayed when the screen is repainted.

       If the −w command-line option is not specified, the default value
       shall be set to the value of the LINES environment variable. If the
       LINES environment variable is empty or null, the default shall be the
       number of lines in the display minus 1.

       Setting the window edit option to zero or to a value greater than the
       number of lines in the display minus 1 (either explicitly or based on
       the −w option or the LINES environment variable) shall cause the
       window edit option to be set to the number of lines in the display
       minus 1.

       The baud rate of the terminal line may change the default in an
       implementation-defined manner.

   wrapmargin, wm
       [Default 0]

       If the value of this edit option is zero, it shall have no effect.

       If not in the POSIX locale, the effect of this edit option is
       implementation-defined.

       Otherwise, it shall specify a number of columns from the ending
       margin of the terminal.

       During open and visual text input modes, for each character for which
       any part of the character is displayed in a column that is less than
       wrapmargin columns from the ending margin of the display line, the
       editor shall behave as follows:

        1. If the character triggering this event is a <blank>, it, and all
           immediately preceding <blank> characters on the current line
           entered during the execution of the current text input command,
           shall be discarded, and the editor shall behave as if the user
           had entered a single <newline> instead. In addition, if the next
           user-entered character is a <space>, it shall be discarded as
           well.

        2. Otherwise, if there are one or more <blank> characters on the
           current line immediately preceding the last group of inserted
           non-<blank> characters which was entered during the execution of
           the current text input command, the <blank> characters shall be
           replaced as if the user had entered a single <newline> instead.

       If the autoindent edit option is set, and the events described in 1.
       or 2. are performed, any <blank> characters at or after the cursor in
       the current line shall be discarded.

       The ending margin shall be determined by the system or overridden by
       the user, as described for COLUMNS in the ENVIRONMENT VARIABLES
       section and the Base Definitions volume of POSIX.1‐2008, Chapter 8,
       Environment Variables.

   wrapscan, ws
       [Default set]

       If wrapscan is set, searches (the ex / or ?  addresses, or open and
       visual mode /, ?, N, and n commands) shall wrap around the beginning
       or end of the edit buffer; when unset, searches shall stop at the
       beginning or end of the edit buffer.

   writeany, wa
       [Default unset]

       If writeany is set, some of the checks performed when executing the
       ex write commands shall be inhibited, as described in editor option
       autowrite.

EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       When any error is encountered and the standard input is not a
       terminal device file, ex shall not write the file or return to
       command or text input mode, and shall terminate with a non-zero exit
       status.

       Otherwise, when an unrecoverable error is encountered, it shall be
       equivalent to a SIGHUP asynchronous event.

       Otherwise, when an error is encountered, the editor shall behave as
       specified in Command Line Parsing in ex.

       The following sections are informative.

APPLICATION USAGE         top

       If a SIGSEGV signal is received while ex is saving a file, the file
       might not be successfully saved.

       The next command can accept more than one file, so usage such as:

           next `ls [abc]*`

       is valid; it would not be valid for the edit or read commands, for
       example, because they expect only one file and unspecified results
       occur.

EXAMPLES         top

       None.

RATIONALE         top

       The ex/vi specification is based on the historical practice found in
       the 4 BSD and System V implementations of ex and vi.

       A restricted editor (both the historical red utility and
       modifications to ex) were considered and rejected for inclusion.
       Neither option provided the level of security that users might
       expect.

       It is recognized that ex visual mode and related features would be
       difficult, if not impossible, to implement satisfactorily on a block-
       mode terminal, or a terminal without any form of cursor addressing;
       thus, it is not a mandatory requirement that such features should
       work on all terminals. It is the intention, however, that an ex
       implementation should provide the full set of capabilities on all
       terminals capable of supporting them.

   Options
       The −c replacement for +command was inspired by the −e option of sed.
       Historically, all such commands (see edit and next as well) were
       executed from the last line of the edit buffer. This meant, for
       example, that "+/pattern" would fail unless the wrapscan option was
       set. POSIX.1‐2008 requires conformance to historical practice. The
       +command option is no longer specified by POSIX.1‐2008 but may be
       present in some implementations. Historically, some implementations
       restricted the ex commands that could be listed as part of the
       command line arguments.  For consistency, POSIX.1‐2008 does not
       permit these restrictions.

       In historical implementations of the editor, the −R option (and the
       readonly edit option) only prevented overwriting of files; appending
       to files was still permitted, mapping loosely into the csh noclobber
       variable. Some implementations, however, have not followed this
       semantic, and readonly does not permit appending either. POSIX.1‐2008
       follows the latter practice, believing that it is a more obvious and
       intuitive meaning of readonly.

       The −s option suppresses all interactive user feedback and is useful
       for editing scripts in batch jobs. The list of specific effects is
       historical practice. The terminal type ``incapable of supporting open
       and visual modes'' has historically been named ``dumb''.

       The −t option was required because the ctags utility appears in
       POSIX.1‐2008 and the option is available in all historical
       implementations of ex.

       Historically, the ex and vi utilities accepted a −x option, which did
       encryption based on the algorithm found in the historical crypt
       utility. The −x option for encryption, and the associated crypt
       utility, were omitted because the algorithm used was not specifiable
       and the export control laws of some nations make it difficult to
       export cryptographic technology. In addition, it did not historically
       provide the level of security that users might expect.

   Standard Input
       An end-of-file condition is not equivalent to an end-of-file
       character.  A common end-of-file character, <control>‐D, is
       historically an ex command.

       There was no maximum line length in historical implementations of ex.
       Specifically, as it was parsed in chunks, the addresses had a
       different maximum length than the filenames. Further, the maximum
       line buffer size was declared as BUFSIZ, which was different lengths
       on different systems. This version selected the value of {LINE_MAX}
       to impose a reasonable restriction on portable usage of ex and to aid
       test suite writers in their development of realistic tests that
       exercise this limit.

   Input Files
       It was an explicit decision by the standard developers that a
       <newline> be added to any file lacking one. It was believed that this
       feature of ex and vi was relied on by users in order to make text
       files lacking a trailing <newline> more portable. It is recognized
       that this will require a user-specified option or extension for
       implementations that permit ex and vi to edit files of type other
       than text if such files are not otherwise identified by the system.
       It was agreed that the ability to edit files of arbitrary type can be
       useful, but it was not considered necessary to mandate that an ex or
       vi implementation be required to handle files other than text files.

       The paragraph in the INPUT FILES section, ``By default, ...'', is
       intended to close a long-standing security problem in ex and vi; that
       of the ``modeline'' or ``modelines'' edit option. This feature allows
       any line in the first or last five lines of the file containing the
       strings "ex:" or "vi:" (and, apparently, "ei:" or "vx:") to be a line
       containing editor commands, and ex interprets all the text up to the
       next ':' or <newline> as a command. Consider the consequences, for
       example, of an unsuspecting user using ex or vi as the editor when
       replying to a mail message in which a line such as:

           ex:! rm −rf :

       appeared in the signature lines. The standard developers believed
       strongly that an editor should not by default interpret any lines of
       a file. Vendors are strongly urged to delete this feature from their
       implementations of ex and vi.

   Asynchronous Events
       The intention of the phrase ``complete write'' is that the entire
       edit buffer be written to stable storage. The note regarding
       temporary files is intended for implementations that use temporary
       files to back edit buffers unnamed by the user.

       Historically, SIGQUIT was ignored by ex, but was the equivalent of
       the Q command in visual mode; that is, it exited visual mode and
       entered ex mode. POSIX.1‐2008 permits, but does not require, this
       behavior. Historically, SIGINT was often used by vi users to
       terminate text input mode (<control>‐C is often easier to enter than
       <ESC>).  Some implementations of vi alerted the terminal on this
       event, and some did not. POSIX.1‐2008 requires that SIGINT behave
       identically to <ESC>, and that the terminal not be alerted.

       Historically, suspending the ex editor during text input mode was
       similar to SIGINT, as completed lines were retained, but any partial
       line discarded, and the editor returned to command mode. POSIX.1‐2008
       is silent on this issue; implementations are encouraged to follow
       historical practice, where possible.

       Historically, the vi editor did not treat SIGTSTP as an asynchronous
       event, and it was therefore impossible to suspend the editor in
       visual text input mode.  There are two major reasons for this. The
       first is that SIGTSTP is a broadcast signal on UNIX systems, and the
       chain of events where the shell execs an application that then execs
       vi usually caused confusion for the terminal state if SIGTSTP was
       delivered to the process group in the default manner. The second was
       that most implementations of the UNIX curses package did not handle
       SIGTSTP safely, and the receipt of SIGTSTP at the wrong time would
       cause them to crash. POSIX.1‐2008 is silent on this issue;
       implementations are encouraged to treat suspension as an asynchronous
       event if possible.

       Historically, modifications to the edit buffer made before SIGINT
       interrupted an operation were retained; that is, anywhere from zero
       to all of the lines to be modified might have been modified by the
       time the SIGINT arrived. These changes were not discarded by the
       arrival of SIGINT. POSIX.1‐2008 permits this behavior, noting that
       the undo command is required to be able to undo these partially
       completed commands.

       The action taken for signals other than SIGINT, SIGCONT, SIGHUP, and
       SIGTERM is unspecified because some implementations attempt to save
       the edit buffer in a useful state when other signals are received.

   Standard Error
       For ex/vi, diagnostic messages are those messages reported as a
       result of a failed attempt to invoke ex or vi, such as invalid
       options or insufficient resources, or an abnormal termination
       condition. Diagnostic messages should not be confused with the error
       messages generated by inappropriate or illegal user commands.

   Initialization in ex and vi
       If an ex command (other than cd, chdir, or source) has a filename
       argument, one or both of the alternate and current pathnames will be
       set. Informally, they are set as follows:

        1. If the ex command is one that replaces the contents of the edit
           buffer, and it succeeds, the current pathname will be set to the
           filename argument (the first filename argument in the case of the
           next command) and the alternate pathname will be set to the
           previous current pathname, if there was one.

        2. In the case of the file read/write forms of the read and write
           commands, if there is no current pathname, the current pathname
           will be set to the filename argument.

        3. Otherwise, the alternate pathname will be set to the filename
           argument.

       For example, :edit foo and :recover foo, when successful, set the
       current pathname, and, if there was a previous current pathname, the
       alternate pathname. The commands :write, !command, and :edit set
       neither the current or alternate pathnames. If the :edit foo command
       were to fail for some reason, the alternate pathname would be set.
       The read and write commands set the alternate pathname to their file
       argument, unless the current pathname is not set, in which case they
       set the current pathname to their file arguments. The alternate
       pathname was not historically set by the :source command.
       POSIX.1‐2008 requires conformance to historical practice.
       Implementations adding commands that take filenames as arguments are
       encouraged to set the alternate pathname as described here.

       Historically, ex and vi read the .exrc file in the $HOME directory
       twice, if the editor was executed in the $HOME directory.
       POSIX.1‐2008 prohibits this behavior.

       Historically, the 4 BSD ex and vi read the $HOME and local .exrc
       files if they were owned by the real ID of the user, or the sourceany
       option was set, regardless of other considerations. This was a
       security problem because it is possible to put normal UNIX system
       commands inside a .exrc file. POSIX.1‐2008 does not specify the
       sourceany option, and historical implementations are encouraged to
       delete it.

       The .exrc files must be owned by the real ID of the user, and not
       writable by anyone other than the owner. The appropriate privileges
       exception is intended to permit users to acquire special privileges,
       but continue to use the .exrc files in their home directories.

       System V Release 3.2 and later vi implementations added the option
       [no]exrc.  The behavior is that local .exrc files are read-only if
       the exrc option is set. The default for the exrc option was off, so
       by default, local .exrc files were not read. The problem this was
       intended to solve was that System V permitted users to give away
       files, so there is no possible ownership or writeability test to
       ensure that the file is safe. This is still a security problem on
       systems where users can give away files, but there is nothing
       additional that POSIX.1‐2008 can do. The implementation-defined
       exception is intended to permit groups to have local .exrc files that
       are shared by users, by creating pseudo-users to own the shared
       files.

       POSIX.1‐2008 does not mention system-wide ex and vi start-up files.
       While they exist in several implementations of ex and vi, they are
       not present in any implementations considered historical practice by
       POSIX.1‐2008. Implementations that have such files should use them
       only if they are owned by the real user ID or an appropriate user
       (for example, root on UNIX systems) and if they are not writable by
       any user other than their owner. System-wide start-up files should be
       read before the EXINIT variable, $HOME/.exrc, or local .exrc files
       are evaluated.

       Historically, any ex command could be entered in the EXINIT variable
       or the .exrc file, although ones requiring that the edit buffer
       already contain lines of text generally caused historical
       implementations of the editor to drop core.  POSIX.1‐2008 requires
       that any ex command be permitted in the EXINIT variable and .exrc
       files, for simplicity of specification and consistency, although many
       of them will obviously fail under many circumstances.

       The initialization of the contents of the edit buffer uses the phrase
       ``the effect shall be'' with regard to various ex commands. The
       intent of this phrase is that edit buffer contents loaded during the
       initialization phase not be lost; that is, loading the edit buffer
       should fail if the .exrc file read in the contents of a file and did
       not subsequently write the edit buffer. An additional intent of this
       phrase is to specify that the initial current line and column is set
       as specified for the individual ex commands.

       Historically, the −t option behaved as if the tag search were a
       +command; that is, it was executed from the last line of the file
       specified by the tag. This resulted in the search failing if the
       pattern was a forward search pattern and the wrapscan edit option was
       not set. POSIX.1‐2008 does not permit this behavior, requiring that
       the search for the tag pattern be performed on the entire file, and,
       if not found, that the current line be set to a more reasonable
       location in the file.

       Historically, the empty edit buffer presented for editing when a file
       was not specified by the user was unnamed. This is permitted by
       POSIX.1‐2008; however, implementations are encouraged to provide
       users a temporary filename for this buffer because it permits them
       the use of ex commands that use the current pathname during temporary
       edit sessions.

       Historically, the file specified using the −t option was not part of
       the current argument list. This practice is permitted by
       POSIX.1‐2008; however, implementations are encouraged to include its
       name in the current argument list for consistency.

       Historically, the −c command was generally not executed until a file
       that already exists was edited. POSIX.1‐2008 requires conformance to
       this historical practice.  Commands that could cause the −c command
       to be executed include the ex commands edit, next, recover, rewind,
       and tag, and the vi commands <control>‐^ and <control>‐].
       Historically, reading a file into an edit buffer did not cause the −c
       command to be executed (even though it might set the current
       pathname) with the exception that it did cause the −c command to be
       executed if: the editor was in ex mode, the edit buffer had no
       current pathname, the edit buffer was empty, and no read commands had
       yet been attempted. For consistency and simplicity of specification,
       POSIX.1‐2008 does not permit this behavior.

       Historically, the −r option was the same as a normal edit session if
       there was no recovery information available for the file. This
       allowed users to enter:

           vi −r *.c

       and recover whatever files were recoverable. In some implementations,
       recovery was attempted only on the first file named, and the file was
       not entered into the argument list; in others, recovery was attempted
       for each file named. In addition, some historical implementations
       ignored −r if −t was specified or did not support command line file
       arguments with the −t option. For consistency and simplicity of
       specification, POSIX.1‐2008 disallows these special cases, and
       requires that recovery be attempted the first time each file is
       edited.

       Historically, vi initialized the ` and ' marks, but ex did not. This
       meant that if the first command in ex mode was visual or if an ex
       command was executed first (for example, vi +10 file), vi was entered
       without the marks being initialized. Because the standard developers
       believed the marks to be generally useful, and for consistency and
       simplicity of specification, POSIX.1‐2008 requires that they always
       be initialized if in open or visual mode, or if in ex mode and the
       edit buffer is not empty. Not initializing it in ex mode if the edit
       buffer is empty is historical practice; however, it has always been
       possible to set (and use) marks in empty edit buffers in open and
       visual mode edit sessions.

   Addressing
       Historically, ex and vi accepted the additional addressing forms '\/'
       and '\?'.  They were equivalent to "//" and "??", respectively. They
       are not required by POSIX.1‐2008, mostly because nobody can remember
       whether they ever did anything different historically.

       Historically, ex and vi permitted an address of zero for several
       commands, and permitted the % address in empty files for others. For
       consistency, POSIX.1‐2008 requires support for the former in the few
       commands where it makes sense, and disallows it otherwise. In
       addition, because POSIX.1‐2008 requires that % be logically
       equivalent to "1,$", it is also supported where it makes sense and
       disallowed otherwise.

       Historically, the % address could not be followed by further
       addresses. For consistency and simplicity of specification,
       POSIX.1‐2008 requires that additional addresses be supported.

       All of the following are valid addresses:

       +++       Three lines after the current line.

       /re/−     One line before the next occurrence of re.

       −2        Two lines before the current line.

       3 −−−− 2  Line one (note intermediate negative address).

       1 2 3     Line six.

       Any number of addresses can be provided to commands taking addresses;
       for example, "1,2,3,4,5p" prints lines 4 and 5, because two is the
       greatest valid number of addresses accepted by the print command.
       This, in combination with the <semicolon> delimiter, permits users to
       create commands based on ordered patterns in the file. For example,
       the command 3;/foo/;+2print will display the first line after line 3
       that contains the pattern foo, plus the next two lines. Note that the
       address 3; must be evaluated before being discarded because the
       search origin for the /foo/ command depends on this.

       Historically, values could be added to addresses by including them
       after one or more <blank> characters; for example, 3 − 5p wrote the
       seventh line of the file, and /foo/ 5 was the same as /foo/+5.
       However, only absolute values could be added; for example, 5 /foo/
       was an error. POSIX.1‐2008 requires conformance to historical
       practice.  Address offsets are separately specified from addresses
       because they could historically be provided to visual mode search
       commands.

       Historically, any missing addresses defaulted to the current line.
       This was true for leading and trailing <comma>-delimited addresses,
       and for trailing <semicolon>-delimited addresses. For consistency,
       POSIX.1‐2008 requires it for leading <semicolon> addresses as well.

       Historically, ex and vi accepted the '^' character as both an address
       and as a flag offset for commands. In both cases it was identical to
       the '−' character. POSIX.1‐2008 does not require or prohibit this
       behavior.

       Historically, the enhancements to basic regular expressions could be
       used in addressing; for example, '~', '\<', and '\>'.  POSIX.1‐2008
       requires conformance to historical practice; that is, that regular
       expression usage be consistent, and that regular expression
       enhancements be supported wherever regular expressions are used.

   Command Line Parsing in ex
       Historical ex command parsing was even more complex than that
       described here. POSIX.1‐2008 requires the subset of the command
       parsing that the standard developers believed was documented and that
       users could reasonably be expected to use in a portable fashion, and
       that was historically consistent between implementations. (The
       discarded functionality is obscure, at best.)  Historical
       implementations will require changes in order to comply with
       POSIX.1‐2008; however, users are not expected to notice any of these
       changes.  Most of the complexity in ex parsing is to handle three
       special termination cases:

        1. The !, global, v, and the filter versions of the read and write
           commands are delimited by <newline> characters (they can contain
           <vertical-line> characters that are usually shell pipes).

        2. The ex, edit, next, and visual in open and visual mode commands
           all take ex commands, optionally containing <vertical-line>
           characters, as their first arguments.

        3. The s command takes a regular expression as its first argument,
           and uses the delimiting characters to delimit the command.

       Historically, <vertical-line> characters in the +command argument of
       the ex, edit, next, vi, and visual commands, and in the pattern and
       replacement parts of the s command, did not delimit the command, and
       in the filter cases for read and write, and the !, global, and v
       commands, they did not delimit the command at all. For example, the
       following commands are all valid:

           :edit +25 | s/abc/ABC/ file.c
           :s/ | /PIPE/
           :read !spell % | columnate
           :global/pattern/p | l
           :s/a/b/ | s/c/d | set

       Historically, empty or <blank> filled lines in .exrc files and
       sourced files (as well as EXINIT variables and ex command scripts)
       were treated as default commands; that is, print commands.
       POSIX.1‐2008 specifically requires that they be ignored when
       encountered in .exrc and sourced files to eliminate a common source
       of new user error.

       Historically, ex commands with multiple adjacent (or
       <blank>-separated) vertical lines were handled oddly when executed
       from ex mode. For example, the command ||| <carriage-return>, when
       the cursor was on line 1, displayed lines 2, 3, and 5 of the file.
       In addition, the command | would only display the line after the next
       line, instead of the next two lines. The former worked more logically
       when executed from vi mode, and displayed lines 2, 3, and 4.
       POSIX.1‐2008 requires the vi behavior; that is, a single default
       command and line number increment for each command separator, and
       trailing <newline> characters after <vertical-line> separators are
       discarded.

       Historically, ex permitted a single extra <colon> as a leading
       command character; for example, :g/pattern/:p was a valid command.
       POSIX.1‐2008 generalizes this to require that any number of leading
       <colon> characters be stripped.

       Historically, any prefix of the delete command could be followed
       without intervening <blank> characters by a flag character because in
       the command d p, p is interpreted as the buffer p.  POSIX.1‐2008
       requires conformance to historical practice.

       Historically, the k command could be followed by the mark name
       without intervening <blank> characters. POSIX.1‐2008 requires
       conformance to historical practice.

       Historically, the s command could be immediately followed by flag and
       option characters; for example, s/e/E/|s|sgc3p was a valid command.
       However, flag characters could not stand alone; for example, the
       commands sp and s l would fail, while the command sgp and s gl would
       succeed. (Obviously, the '#' flag character was used as a delimiter
       character if it followed the command.) Another issue was that option
       characters had to precede flag characters even when the command was
       fully specified; for example, the command s/e/E/pg would fail, while
       the command s/e/E/gp would succeed. POSIX.1‐2008 requires conformance
       to historical practice.

       Historically, the first command name that had a prefix matching the
       input from the user was the executed command; for example, ve, ver,
       and vers all executed the version command. Commands were in a
       specific order, however, so that a matched append, not abbreviate.
       POSIX.1‐2008 requires conformance to historical practice. The
       restriction on command search order for implementations with
       extensions is to avoid the addition of commands such that the
       historical prefixes would fail to work portably.

       Historical implementations of ex and vi did not correctly handle
       multiple ex commands, separated by <vertical-line> characters, that
       entered or exited visual mode or the editor. Because implementations
       of vi exist that do not exhibit this failure mode, POSIX.1‐2008 does
       not permit it.

       The requirement that alphabetic command names consist of all
       following alphabetic characters up to the next non-alphabetic
       character means that alphabetic command names must be separated from
       their arguments by one or more non-alphabetic characters, normally a
       <blank> or '!'  character, except as specified for the exceptions,
       the delete, k, and s commands.

       Historically, the repeated execution of the ex default print commands
       (<control>‐D, eof, <newline>, <carriage-return>) erased any prompting
       character and displayed the next lines without scrolling the
       terminal; that is, immediately below any previously displayed lines.
       This provided a cleaner presentation of the lines in the file for the
       user. POSIX.1‐2008 does not require this behavior because it may be
       impossible in some situations; however, implementations are strongly
       encouraged to provide this semantic if possible.

       Historically, it was possible to change files in the middle of a
       command, and have the rest of the command executed in the new file;
       for example:

           :edit +25 file.c | s/abc/ABC/ | 1

       was a valid command, and the substitution was attempted in the newly
       edited file. POSIX.1‐2008 requires conformance to historical
       practice. The following commands are examples that exercise the ex
       parser:

           echo 'foo | bar' > file1; echo 'foo/bar' > file2;
           vi
           :edit +1 | s/|/PIPE/ | w file1 | e file2 | 1 | s/\//SLASH/ | wq

       Historically, there was no protection in editor implementations to
       avoid ex global, v, @, or * commands changing edit buffers during
       execution of their associated commands. Because this would almost
       invariably result in catastrophic failure of the editor, and
       implementations exist that do exhibit these problems, POSIX.1‐2008
       requires that changing the edit buffer during a global or v command,
       or during a @ or * command for which there will be more than a single
       execution, be an error. Implementations supporting multiple edit
       buffers simultaneously are strongly encouraged to apply the same
       semantics to switching between buffers as well.

       The ex command quoting required by POSIX.1‐2008 is a superset of the
       quoting in historical implementations of the editor. For example, it
       was not historically possible to escape a <blank> in a filename; for
       example, :edit foo\\\ bar would report that too many filenames had
       been entered for the edit command, and there was no method of
       escaping a <blank> in the first argument of an edit, ex, next, or
       visual command at all. POSIX.1‐2008 extends historical practice,
       requiring that quoting behavior be made consistent across all ex
       commands, except for the map, unmap, abbreviate, and unabbreviate
       commands, which historically used <control>‐V instead of <backslash>
       characters for quoting. For those four commands, POSIX.1‐2008
       requires conformance to historical practice.

       Backslash quoting in ex is non-intuitive.  <backslash>-escapes are
       ignored unless they escape a special character; for example, when
       performing file argument expansion, the string "\\%" is equivalent to
       '\%', not "\<current pathname>".  This can be confusing for users
       because <backslash> is usually one of the characters that causes
       shell expansion to be performed, and therefore shell quoting rules
       must be taken into consideration. Generally, quoting characters are
       only considered if they escape a special character, and a quoting
       character must be provided for each layer of parsing for which the
       character is special. As another example, only a single <backslash>
       is necessary for the '\l' sequence in substitute replacement
       patterns, because the character 'l' is not special to any parsing
       layer above it.

       <control>‐V quoting in ex is slightly different from backslash
       quoting. In the four commands where <control>‐V quoting applies
       (abbreviate, unabbreviate, map, and unmap), any character may be
       escaped by a <control>‐V whether it would have a special meaning or
       not. POSIX.1‐2008 requires conformance to historical practice.

       Historical implementations of the editor did not require delimiters
       within character classes to be escaped; for example, the command
       :s/[/]// on the string "xxx/yyy" would delete the '/' from the
       string. POSIX.1‐2008 disallows this historical practice for
       consistency and because it places a large burden on implementations
       by requiring that knowledge of regular expressions be built into the
       editor parser.

       Historically, quoting <newline> characters in ex commands was handled
       inconsistently. In most cases, the <newline> character always
       terminated the command, regardless of any preceding escape character,
       because <backslash> characters did not escape <newline> characters
       for most ex commands. However, some ex commands (for example, s, map,
       and abbreviation) permitted <newline> characters to be escaped
       (although in the case of map and abbreviation, <control>‐V characters
       escaped them instead of <backslash> characters). This was true in not
       only the command line, but also .exrc and sourced files. For example,
       the command:

           map = foo<control-V><newline>bar

       would succeed, although it was sometimes difficult to get the
       <control>‐V and the inserted <newline> passed to the ex parser. For
       consistency and simplicity of specification, POSIX.1‐2008 requires
       that it be possible to escape <newline> characters in ex commands at
       all times, using <backslash> characters for most ex commands, and
       using <control>‐V characters for the map and abbreviation commands.
       For example, the command print<newline>list is required to be parsed
       as the single command print<newline>list.  While this differs from
       historical practice, POSIX.1‐2008 developers believed it unlikely
       that any script or user depended on the historical behavior.

       Historically, an error in a command specified using the −c option did
       not cause the rest of the −c commands to be discarded. POSIX.1‐2008
       disallows this for consistency with mapped keys, the @, global,
       source, and v commands, the EXINIT environment variable, and the
       .exrc files.

   Input Editing in ex
       One of the common uses of the historical ex editor is over slow
       network connections. Editors that run in canonical mode can require
       far less traffic to and from, and far less processing on, the host
       machine, as well as more easily supporting block-mode terminals. For
       these reasons, POSIX.1‐2008 requires that ex be implemented using
       canonical mode input processing, as was done historically.

       POSIX.1‐2008 does not require the historical 4 BSD input editing
       characters ``word erase'' or ``literal next''. For this reason, it is
       unspecified how they are handled by ex, although they must have the
       required effect. Implementations that resolve them after the line has
       been ended using a <newline> or <control>‐M character, and
       implementations that rely on the underlying system terminal support
       for this processing, are both conforming.  Implementations are
       strongly urged to use the underlying system functionality, if at all
       possible, for compatibility with other system text input interfaces.

       Historically, when the eof character was used to decrement the
       autoindent level, the cursor moved to display the new end of the
       autoindent characters, but did not move the cursor to a new line, nor
       did it erase the <control>‐D character from the line. POSIX.1‐2008
       does not specify that the cursor remain on the same line or that the
       rest of the line is erased; however, implementations are strongly
       encouraged to provide the best possible user interface; that is, the
       cursor should remain on the same line, and any <control>‐D character
       on the line should be erased.

       POSIX.1‐2008 does not require the historical 4 BSD input editing
       character ``reprint'', traditionally <control>‐R, which redisplayed
       the current input from the user. For this reason, and because the
       functionality cannot be implemented after the line has been
       terminated by the user, POSIX.1‐2008 makes no requirements about this
       functionality. Implementations are strongly urged to make this
       historical functionality available, if possible.

       Historically, <control>‐Q did not perform a literal next function in
       ex, as it did in vi.  POSIX.1‐2008 requires conformance to historical
       practice to avoid breaking historical ex scripts and .exrc files.

   eof
       Whether the eof character immediately modifies the autoindent
       characters in the prompt is left unspecified so that implementations
       can conform in the presence of systems that do not support this
       functionality. Implementations are encouraged to modify the line and
       redisplay it immediately, if possible.

       The specification of the handling of the eof character differs from
       historical practice only in that eof characters are not discarded if
       they follow normal characters in the text input. Historically, they
       were always discarded.

   Command Descriptions in ex
       Historically, several commands (for example, global, v, visual, s,
       write, wq, yank, !, <, >, &, and ~) were executable in empty files
       (that is, the default address(es) were 0), or permitted explicit
       addresses of 0 (for example, 0 was a valid address, or 0,0 was a
       valid range). Addresses of 0, or command execution in an empty file,
       make sense only for commands that add new text to the edit buffer or
       write commands (because users may wish to write empty files).
       POSIX.1‐2008 requires this behavior for such commands and disallows
       it otherwise, for consistency and simplicity of specification.

       A count to an ex command has been historically corrected to be no
       greater than the last line in a file; for example, in a five-line
       file, the command 1,6print would fail, but the command 1print300
       would succeed. POSIX.1‐2008 requires conformance to historical
       practice.

       Historically, the use of flags in ex commands could be obscure.
       General historical practice was as described by POSIX.1‐2008, but
       there were some special cases. For instance, the list, number, and
       print commands ignored trailing address offsets; for example, 3p +++#
       would display line 3, and 3 would be the current line after the
       execution of the command. The open and visual commands ignored both
       the trailing offsets and the trailing flags.  Also, flags specified
       to the open and visual commands interacted badly with the list edit
       option, and setting and then unsetting it during the open/visual
       session would cause vi to stop displaying lines in the specified
       format. For consistency and simplicity of specification, POSIX.1‐2008
       does not permit any of these exceptions to the general rule.

       POSIX.1‐2008 uses the word copy in several places when discussing
       buffers. This is not intended to imply implementation.

       Historically, ex users could not specify numeric buffers because of
       the ambiguity this would cause; for example, in the command
       3 delete 2, it is unclear whether 2 is a buffer name or a count.
       POSIX.1‐2008 requires conformance to historical practice by default,
       but does not preclude extensions.

       Historically, the contents of the unnamed buffer were frequently
       discarded after commands that did not explicitly affect it; for
       example, when using the edit command to switch files. For consistency
       and simplicity of specification, POSIX.1‐2008 does not permit this
       behavior.

       The ex utility did not historically have access to the numeric
       buffers, and, furthermore, deleting lines in ex did not modify their
       contents. For example, if, after doing a delete in vi, the user
       switched to ex, did another delete, and then switched back to vi, the
       contents of the numeric buffers would not have changed. POSIX.1‐2008
       requires conformance to historical practice. Numeric buffers are
       described in the ex utility in order to confine the description of
       buffers to a single location in POSIX.1‐2008.

       The metacharacters that trigger shell expansion in file arguments
       match historical practice, as does the method for doing shell
       expansion. Implementations wishing to provide users with the
       flexibility to alter the set of metacharacters are encouraged to
       provide a shellmeta string edit option.

       Historically, ex commands executed from vi refreshed the screen when
       it did not strictly need to do so; for example, :!date > /dev/null
       does not require a screen refresh because the output of the UNIX date
       command requires only a single line of the screen. POSIX.1‐2008
       requires that the screen be refreshed if it has been overwritten, but
       makes no requirements as to how an implementation should make that
       determination. Implementations may prompt and refresh the screen
       regardless.

   Abbreviate
       Historical practice was that characters that were entered as part of
       an abbreviation replacement were subject to map expansions, the
       showmatch edit option, further abbreviation expansions, and so on;
       that is, they were logically pushed onto the terminal input queue,
       and were not a simple replacement. POSIX.1‐2008 requires conformance
       to historical practice.  Historical practice was that whenever a non-
       word character (that had not been escaped by a <control>‐V) was
       entered after a word character, vi would check for abbreviations. The
       check was based on the type of the character entered before the word
       character of the word/non-word pair that triggered the check. The
       word character of the word/non-word pair that triggered the check and
       all characters entered before the trigger pair that were of that type
       were included in the check, with the exception of <blank> characters,
       which always delimited the abbreviation.

       This means that, for the abbreviation to work, the lhs must end with
       a word character, there can be no transitions from word to non-word
       characters (or vice versa) other than between the last and next-to-
       last characters in the lhs, and there can be no <blank> characters in
       the lhs.  In addition, because of the historical quoting rules, it
       was impossible to enter a literal <control>‐V in the lhs.
       POSIX.1‐2008 requires conformance to historical practice. Historical
       implementations did not inform users when abbreviations that could
       never be used were entered; implementations are strongly encouraged
       to do so.

       For example, the following abbreviations will work:

           :ab (p  REPLACE
           :ab p   REPLACE
           :ab ((p REPLACE

       The following abbreviations will not work:

           :ab (   REPLACE
           :ab (pp REPLACE

       Historical practice is that words on the vi colon command line were
       subject to abbreviation expansion, including the arguments to the
       abbrev (and more interestingly) the unabbrev command. Because there
       are implementations that do not do abbreviation expansion for the
       first argument to those commands, this is permitted, but not
       required, by POSIX.1‐2008. However, the following sequence:

           :ab foo bar
           :ab foo baz

       resulted in the addition of an abbreviation of "baz" for the string
       "bar" in historical ex/vi, and the sequence:

           :ab foo1 bar
           :ab foo2 bar
           :unabbreviate foo2

       deleted the abbreviation "foo1", not "foo2".  These behaviors are not
       permitted by POSIX.1‐2008 because they clearly violate the
       expectations of the user.

       It was historical practice that <control>‐V, not <backslash>,
       characters be interpreted as escaping subsequent characters in the
       abbreviate command. POSIX.1‐2008 requires conformance to historical
       practice; however, it should be noted that an abbreviation containing
       a <blank> will never work.

   Append
       Historically, any text following a <vertical-line> command separator
       after an append, change, or insert command became part of the insert
       text. For example, in the command:

           :g/pattern/append|stuff1

       a line containing the text "stuff1" would be appended to each line
       matching pattern. It was also historically valid to enter:

           :append|stuff1
           stuff2
           .

       and the text on the ex command line would be appended along with the
       text inserted after it.  There was an historical bug, however, that
       the user had to enter two terminating lines (the '.'  lines) to
       terminate text input mode in this case. POSIX.1‐2008 requires
       conformance to historical practice, but disallows the historical need
       for multiple terminating lines.

   Change
       See the RATIONALE for the append command. Historical practice for
       cursor positioning after the change command when no text is input, is
       as described in POSIX.1‐2008. However, one System V implementation is
       known to have been modified such that the cursor is positioned on the
       first address specified, and not on the line before the first
       address. POSIX.1‐2008 disallows this modification for consistency.

       Historically, the change command did not support buffer arguments,
       although some implementations allow the specification of an optional
       buffer. This behavior is neither required nor disallowed by
       POSIX.1‐2008.

   Change Directory
       A common extension in ex implementations is to use the elements of a
       cdpath edit option as prefix directories for path arguments to chdir
       that are relative pathnames and that do not have '.'  or ".." as
       their first component. Elements in the cdpath edit option are
       <colon>-separated.  The initial value of the cdpath edit option is
       the value of the shell CDPATH environment variable. This feature was
       not included in POSIX.1‐2008 because it does not exist in any of the
       implementations considered historical practice.

   Copy
       Historical implementations of ex permitted copies to lines inside of
       the specified range; for example, :2,5copy3 was a valid command.
       POSIX.1‐2008 requires conformance to historical practice.

   Delete
       POSIX.1‐2008 requires support for the historical parsing of a delete
       command followed by flags, without any intervening <blank>
       characters. For example:

       1dp     Deletes the first line and prints the line that was second.

       1delep  As for 1dp.

       1d      Deletes the first line, saving it in buffer p.

       1d p1l  (Pee-one-ell.) Deletes the first line, saving it in buffer p,
               and listing the line that was second.

   Edit
       Historically, any ex command could be entered as a +command argument
       to the edit command, although some (for example, insert and append)
       were known to confuse historical implementations. For consistency and
       simplicity of specification, POSIX.1‐2008 requires that any command
       be supported as an argument to the edit command.

       Historically, the command argument was executed with the current line
       set to the last line of the file, regardless of whether the edit
       command was executed from visual mode or not. POSIX.1‐2008 requires
       conformance to historical practice.

       Historically, the +command specified to the edit and next commands
       was delimited by the first <blank>, and there was no way to quote
       them. For consistency, POSIX.1‐2008 requires that the usual ex
       backslash quoting be provided.

       Historically, specifying the +command argument to the edit command
       required a filename to be specified as well; for example, :edit +100
       would always fail. For consistency and simplicity of specification,
       POSIX.1‐2008 does not permit this usage to fail for that reason.

       Historically, only the cursor position of the last file edited was
       remembered by the editor. POSIX.1‐2008 requires that this be
       supported; however, implementations are permitted to remember and
       restore the cursor position for any file previously edited.

   File
       Historical versions of the ex editor file command displayed a current
       line and number of lines in the edit buffer of 0 when the file was
       empty, while the vi <control>‐G command displayed a current line and
       number of lines in the edit buffer of 1 in the same situation.
       POSIX.1‐2008 does not permit this discrepancy, instead requiring that
       a message be displayed indicating that the file is empty.

   Global
       The two-pass operation of the global and v commands is not intended
       to imply implementation, only the required result of the operation.

       The current line and column are set as specified for the individual
       ex commands. This requirement is cumulative; that is, the current
       line and column must track across all the commands executed by the
       global or v commands.

   Insert
       See the RATIONALE for the append command.

       Historically, insert could not be used with an address of zero; that
       is, not when the edit buffer was empty. POSIX.1‐2008 requires that
       this command behave consistently with the append command.

   Join
       The action of the join command in relation to the special characters
       is only defined for the POSIX locale because the correct amount of
       white space after a period varies; in Japanese none is required, in
       French only a single space, and so on.

   List
       The historical output of the list command was potentially ambiguous.
       The standard developers believed correcting this to be more important
       than adhering to historical practice, and POSIX.1‐2008 requires
       unambiguous output.

   Map
       Historically, command mode maps only applied to command names; for
       example, if the character 'x' was mapped to 'y', the command fx
       searched for the 'x' character, not the 'y' character. POSIX.1‐2008
       requires this behavior. Historically, entering <control>‐V as the
       first character of a vi command was an error. Several implementations
       have extended the semantics of vi such that <control>‐V means that
       the subsequent command character is not mapped. This is permitted,
       but not required, by POSIX.1‐2008. Regardless, using <control>‐V to
       escape the second or later character in a sequence of characters that
       might match a map command, or any character in text input mode, is
       historical practice, and stops the entered keys from matching a map.
       POSIX.1‐2008 requires conformance to historical practice.

       Historical implementations permitted digits to be used as a map
       command lhs, but then ignored the map. POSIX.1‐2008 requires that the
       mapped digits not be ignored.

       The historical implementation of the map command did not permit map
       commands that were more than a single character in length if the
       first character was printable. This behavior is permitted, but not
       required, by POSIX.1‐2008.

       Historically, mapped characters were remapped unless the remap edit
       option was not set, or the prefix of the mapped characters matched
       the mapping characters; for example, in the map:

           :map ab abcd

       the characters "ab" were used as is and were not remapped, but the
       characters "cd" were mapped if appropriate. This can cause infinite
       loops in the vi mapping mechanisms. POSIX.1‐2008 requires conformance
       to historical practice, and that such loops be interruptible.

       Text input maps had the same problems with expanding the lhs for the
       ex map!  and unmap!  command as did the ex abbreviate and
       unabbreviate commands. See the RATIONALE for the ex abbreviate
       command. POSIX.1‐2008 requires similar modification of some
       historical practice for the map and unmap commands, as described for
       the abbreviate and unabbreviate commands.

       Historically, maps that were subsets of other maps behaved
       differently depending on the order in which they were defined.  For
       example:

           :map! ab     short
           :map! abc    long

       would always translate the characters "ab" to "short", regardless of
       how fast the characters "abc" were entered. If the entry order was
       reversed:

           :map! abc    long
           :map! ab     short

       the characters "ab" would cause the editor to pause, waiting for the
       completing 'c' character, and the characters might never be mapped to
       "short".  For consistency and simplicity of specification,
       POSIX.1‐2008 requires that the shortest match be used at all times.

       The length of time the editor spends waiting for the characters to
       complete the lhs is unspecified because the timing capabilities of
       systems are often inexact and variable, and it may depend on other
       factors such as the speed of the connection. The time should be long
       enough for the user to be able to complete the sequence, but not long
       enough for the user to have to wait. Some implementations of vi have
       added a keytime option, which permits users to set the number of 0,1
       seconds the editor waits for the completing characters. Because
       mapped terminal function and cursor keys tend to start with an <ESC>
       character, and <ESC> is the key ending vi text input mode, maps
       starting with <ESC> characters are generally exempted from this
       timeout period, or, at least timed out differently.

   Mark
       Historically, users were able to set the ``previous context'' marks
       explicitly. In addition, the ex commands '' and '` and the vi
       commands '', ``, `', and '` all referred to the same mark. In
       addition, the previous context marks were not set if the command,
       with which the address setting the mark was associated, failed.
       POSIX.1‐2008 requires conformance to historical practice.
       Historically, if marked lines were deleted, the mark was also
       deleted, but would reappear if the change was undone. POSIX.1‐2008
       requires conformance to historical practice.

       The description of the special events that set the ` and ' marks
       matches historical practice. For example, historically the command
       /a/,/b/ did not set the ` and ' marks, but the command /a/,/b/delete
       did.

   Next
       Historically, any ex command could be entered as a +command argument
       to the next command, although some (for example, insert and append)
       were known to confuse historical implementations. POSIX.1‐2008
       requires that any command be permitted and that it behave as
       specified. The next command can accept more than one file, so usage
       such as:

           next `ls [abc] `

       is valid; it need not be valid for the edit or read commands, for
       example, because they expect only one filename.

       Historically, the next command behaved differently from the :rewind
       command in that it ignored the force flag if the autowrite flag was
       set. For consistency, POSIX.1‐2008 does not permit this behavior.

       Historically, the next command positioned the cursor as if the file
       had never been edited before, regardless. POSIX.1‐2008 does not
       permit this behavior, for consistency with the edit command.

       Implementations wanting to provide a counterpart to the next command
       that edited the previous file have used the command prev[ious], which
       takes no file argument. POSIX.1‐2008 does not require this command.

   Open
       Historically, the open command would fail if the open edit option was
       not set. POSIX.1‐2008 does not mention the open edit option and does
       not require this behavior. Some historical implementations do not
       permit entering open mode from open or visual mode, only from ex
       mode. For consistency, POSIX.1‐2008 does not permit this behavior.

       Historically, entering open mode from the command line (that is, vi
       +open) resulted in anomalous behaviors; for example, the ex file and
       set commands, and the vi command <control>‐G did not work. For
       consistency, POSIX.1‐2008 does not permit this behavior.

       Historically, the open command only permitted '/' characters to be
       used as the search pattern delimiter. For consistency, POSIX.1‐2008
       requires that the search delimiters used by the s, global, and v
       commands be accepted as well.

   Preserve
       The preserve command does not historically cause the file to be
       considered unmodified for the purposes of future commands that may
       exit the editor. POSIX.1‐2008 requires conformance to historical
       practice.

       Historical documentation stated that mail was not sent to the user
       when preserve was executed; however, historical implementations did
       send mail in this case. POSIX.1‐2008 requires conformance to the
       historical implementations.

   Print
       The writing of NUL by the print command is not specified as a special
       case because the standard developers did not want to require ex to
       support NUL characters. Historically, characters were displayed using
       the ARPA standard mappings, which are as follows:

        1. Printable characters are left alone.

        2. Control characters less than \177 are represented as '^' followed
           by the character offset from the '@' character in the ASCII map;
           for example, \007 is represented as '^G'.

        3. \177 is represented as '^' followed by '?'.

       The display of characters having their eighth bit set was less
       standard. Existing implementations use hex (0x00), octal (\000), and
       a meta-bit display. (The latter displayed bytes that had their eighth
       bit set as the two characters "M−" followed by the seven-bit display
       as described above.) The latter probably has the best claim to
       historical practice because it was used for the −v option of 4 BSD
       and 4 BSD-derived versions of the cat utility since 1980.

       No specific display format is required by POSIX.1‐2008.

       Explicit dependence on the ASCII character set has been avoided where
       possible, hence the use of the phrase an ``implementation-defined
       multi-character sequence'' for the display of non-printable
       characters in preference to the historical usage of, for instance,
       "^I" for the <tab>.  Implementations are encouraged to conform to
       historical practice in the absence of any strong reason to diverge.

       Historically, all ex commands beginning with the letter 'p' could be
       entered using capitalized versions of the commands; for example,
       P[rint], Pre[serve], and Pu[t] were all valid command names.
       POSIX.1‐2008 permits, but does not require, this historical practice
       because capital forms of the commands are used by some
       implementations for other purposes.

   Put
       Historically, an ex put command, executed from open or visual mode,
       was the same as the open or visual mode P command, if the buffer was
       named and was cut in character mode, and the same as the p command if
       the buffer was named and cut in line mode. If the unnamed buffer was
       the source of the text, the entire line from which the text was taken
       was usually put, and the buffer was handled as if in line mode, but
       it was possible to get extremely anomalous behavior. In addition,
       using the Q command to switch into ex mode, and then doing a put
       often resulted in errors as well, such as appending text that was
       unrelated to the (supposed) contents of the buffer. For consistency
       and simplicity of specification, POSIX.1‐2008 does not permit these
       behaviors. All ex put commands are required to operate in line mode,
       and the contents of the buffers are not altered by changing the mode
       of the editor.

   Read
       Historically, an ex read command executed from open or visual mode,
       executed in an empty file, left an empty line as the first line of
       the file. For consistency and simplicity of specification,
       POSIX.1‐2008 does not permit this behavior.  Historically, a read in
       open or visual mode from a program left the cursor at the last line
       read in, not the first. For consistency, POSIX.1‐2008 does not permit
       this behavior.

       Historical implementations of ex were unable to undo read commands
       that read from the output of a program. For consistency, POSIX.1‐2008
       does not permit this behavior.

       Historically, the ex and vi message after a successful read or write
       command specified ``characters'', not ``bytes''. POSIX.1‐2008
       requires that the number of bytes be displayed, not the number of
       characters, because it may be difficult in multi-byte implementations
       to determine the number of characters read. Implementations are
       encouraged to clarify the message displayed to the user.

       Historically, reads were not permitted on files other than type
       regular, except that FIFO files could be read (probably only because
       they did not exist when ex and vi were originally written). Because
       the historical ex evaluated read!  and read !  equivalently, there
       can be no optional way to force the read. POSIX.1‐2008 permits, but
       does not require, this behavior.

   Recover
       Some historical implementations of the editor permitted users to
       recover the edit buffer contents from a previous edit session, and
       then exit without saving those contents (or explicitly discarding
       them). The intent of POSIX.1‐2008 in requiring that the edit buffer
       be treated as already modified is to prevent this user error.

   Rewind
       Historical implementations supported the rewind command when the user
       was editing the first file in the list; that is, the file that the
       rewind command would edit. POSIX.1‐2008 requires conformance to
       historical practice.

   Substitute
       Historically, ex accepted an r option to the s command. The effect of
       the r option was to use the last regular expression used in any
       command as the pattern, the same as the ~ command. The r option is
       not required by POSIX.1‐2008. Historically, the c and g options were
       toggled; for example, the command :s/abc/def/ was the same as
       s/abc/def/ccccgggg.  For simplicity of specification, POSIX.1‐2008
       does not permit this behavior.

       The tilde command is often used to replace the last search RE. For
       example, in the sequence:

           s/red/blue/
           /green
           ~

       the ~ command is equivalent to:

           s/green/blue/

       Historically, ex accepted all of the following forms:

           s/abc/def/
           s/abc/def
           s/abc/
           s/abc

       POSIX.1‐2008 requires conformance to this historical practice.

       The s command presumes that the '^' character only occupies a single
       column in the display. Much of the ex and vi specification presumes
       that the <space> only occupies a single column in the display. There
       are no known character sets for which this is not true.

       Historically, the final column position for the substitute commands
       was based on previous column movements; a search for a pattern
       followed by a substitution would leave the column position unchanged,
       while a 0 command followed by a substitution would change the column
       position to the first non-<blank>.  For consistency and simplicity of
       specification, POSIX.1‐2008 requires that the final column position
       always be set to the first non-<blank>.

   Set
       Historical implementations redisplayed all of the options for each
       occurrence of the all keyword. POSIX.1‐2008 permits, but does not
       require, this behavior.

   Tag
       No requirement is made as to where ex and vi shall look for the file
       referenced by the tag entry. Historical practice has been to look for
       the path found in the tags file, based on the current directory. A
       useful extension found in some implementations is to look based on
       the directory containing the tags file that held the entry, as well.
       No requirement is made as to which reference for the tag in the tags
       file is used. This is deliberate, in order to permit extensions such
       as multiple entries in a tags file for a tag.

       Because users often specify many different tags files, some of which
       need not be relevant or exist at any particular time, POSIX.1‐2008
       requires that error messages about problem tags files be displayed
       only if the requested tag is not found, and then, only once for each
       time that the tag edit option is changed.

       The requirement that the current edit buffer be unmodified is only
       necessary if the file indicated by the tag entry is not the same as
       the current file (as defined by the current pathname). Historically,
       the file would be reloaded if the filename had changed, as well as if
       the filename was different from the current pathname. For consistency
       and simplicity of specification, POSIX.1‐2008 does not permit this
       behavior, requiring that the name be the only factor in the decision.

       Historically, vi only searched for tags in the current file from the
       current cursor to the end of the file, and therefore, if the wrapscan
       option was not set, tags occurring before the current cursor were not
       found. POSIX.1‐2008 considers this a bug, and implementations are
       required to search for the first occurrence in the file, regardless.

   Undo
       The undo description deliberately uses the word ``modified''. The
       undo command is not intended to undo commands that replace the
       contents of the edit buffer, such as edit, next, tag, or recover.

       Cursor positioning after the undo command was inconsistent in the
       historical vi, sometimes attempting to restore the original cursor
       position (global, undo, and v commands), and sometimes, in the
       presence of maps, placing the cursor on the last line added or
       changed instead of the first. POSIX.1‐2008 requires a simplified
       behavior for consistency and simplicity of specification.

   Version
       The version command cannot be exactly specified since there is no
       widely-accepted definition of what the version information should
       contain.  Implementations are encouraged to do something reasonably
       intelligent.

   Write
       Historically, the ex and vi message after a successful read or write
       command specified ``characters'', not ``bytes''. POSIX.1‐2008
       requires that the number of bytes be displayed, not the number of
       characters because it may be difficult in multi-byte implementations
       to determine the number of characters written. Implementations are
       encouraged to clarify the message displayed to the user.

       Implementation-defined tests are permitted so that implementations
       can make additional checks; for example, for locks or file
       modification times.

       Historically, attempting to append to a nonexistent file caused an
       error. It has been left unspecified in POSIX.1‐2008 to permit
       implementations to let the write succeed, so that the append
       semantics are similar to those of the historical csh.

       Historical vi permitted empty edit buffers to be written. However,
       since the way vi got around dealing with ``empty'' files was to
       always have a line in the edit buffer, no matter what, it wrote them
       as files of a single, empty line. POSIX.1‐2008 does not permit this
       behavior.

       Historically, ex restored standard output and standard error to their
       values as of when ex was invoked, before writes to programs were
       performed. This could disturb the terminal configuration as well as
       be a security issue for some terminals. POSIX.1‐2008 does not permit
       this, requiring that the program output be captured and displayed as
       if by the ex print command.

   Adjust Window
       Historically, the line count was set to the value of the scroll
       option if the type character was end-of-file. This feature was broken
       on most historical implementations long ago, however, and is not
       documented anywhere. For this reason, POSIX.1‐2008 is resolutely
       silent.

       Historically, the z command was <blank>-sensitive and z + and z − did
       different things than z+ and z− because the type could not be
       distinguished from a flag. (The commands z .  and z = were
       historically invalid.) POSIX.1‐2008 requires conformance to this
       historical practice.

       Historically, the z command was further <blank>-sensitive in that the
       count could not be <blank>-delimited; for example, the commands z= 5
       and z− 5 were also invalid. Because the count is not ambiguous with
       respect to either the type character or the flags, this is not
       permitted by POSIX.1‐2008.

   Escape
       Historically, ex filter commands only read the standard output of the
       commands, letting standard error appear on the terminal as usual. The
       vi utility, however, read both standard output and standard error.
       POSIX.1‐2008 requires the latter behavior for both ex and vi, for
       consistency.

   Shift Left and Shift Right
       Historically, it was possible to add shift characters to increase the
       effect of the command; for example, <<< outdented (or >>> indented)
       the lines 3 levels of indentation instead of the default 1.
       POSIX.1‐2008 requires conformance to historical practice.

   <control>‐D
       Historically, the <control>‐D command erased the prompt, providing
       the user with an unbroken presentation of lines from the edit buffer.
       This is not required by POSIX.1‐2008; implementations are encouraged
       to provide it if possible.  Historically, the <control>‐D command
       took, and then ignored, a count.  POSIX.1‐2008 does not permit this
       behavior.

   Write Line Number
       Historically, the ex = command, when executed in ex mode in an empty
       edit buffer, reported 0, and from open or visual mode, reported 1.
       For consistency and simplicity of specification, POSIX.1‐2008 does
       not permit this behavior.

   Execute
       Historically, ex did not correctly handle the inclusion of text input
       commands (that is, append, insert, and change) in executed buffers.
       POSIX.1‐2008 does not permit this exclusion for consistency.

       Historically, the logical contents of the buffer being executed did
       not change if the buffer itself were modified by the commands being
       executed; that is, buffer execution did not support self-modifying
       code. POSIX.1‐2008 requires conformance to historical practice.

       Historically, the @ command took a range of lines, and the @ buffer
       was executed once per line, with the current line ('.')  set to each
       specified line. POSIX.1‐2008 requires conformance to historical
       practice.

       Some historical implementations did not notice if errors occurred
       during buffer execution. This, coupled with the ability to specify a
       range of lines for the ex @ command, makes it trivial to cause them
       to drop core.  POSIX.1‐2008 requires that implementations stop buffer
       execution if any error occurs, if the specified line doesn't exist,
       or if the contents of the edit buffer itself are replaced (for
       example, the buffer executes the ex :edit command).

   Regular Expressions in ex
       Historical practice is that the characters in the replacement part of
       the last s command—that is, those matched by entering a '~' in the
       regular expression—were not further expanded by the regular
       expression engine. So, if the characters contained the string "a.,"
       they would match 'a' followed by ".," and not 'a' followed by any
       character. POSIX.1‐2008 requires conformance to historical practice.

   Edit Options in ex
       The following paragraphs describe the historical behavior of some
       edit options that were not, for whatever reason, included in
       POSIX.1‐2008.  Implementations are strongly encouraged to only use
       these names if the functionality described here is fully supported.

       extended  The extended edit option has been used in some
                 implementations of vi to provide extended regular
                 expressions instead of basic regular expressions This
                 option was omitted from POSIX.1‐2008 because it is not
                 widespread historical practice.

       flash     The flash edit option historically caused the screen to
                 flash instead of beeping on error. This option was omitted
                 from POSIX.1‐2008 because it is not found in some
                 historical implementations.

       hardtabs  The hardtabs edit option historically defined the number of
                 columns between hardware tab settings. This option was
                 omitted from POSIX.1‐2008 because it was believed to no
                 longer be generally useful.

       modeline  The modeline (sometimes named modelines) edit option
                 historically caused ex or vi to read the five first and
                 last lines of the file for editor commands.  This option is
                 a security problem, and vendors are strongly encouraged to
                 delete it from historical implementations.

       open      The open edit option historically disallowed the ex open
                 and visual commands. This edit option was omitted because
                 these commands are required by POSIX.1‐2008.

       optimize  The optimize edit option historically expedited text
                 throughput by setting the terminal to not do automatic
                 <carriage-return> characters when printing more than one
                 logical line of output. This option was omitted from
                 POSIX.1‐2008 because it was intended for terminals without
                 addressable cursors, which are rarely, if ever, still used.

       ruler     The ruler edit option has been used in some implementations
                 of vi to present a current row/column ruler for the user.
                 This option was omitted from POSIX.1‐2008 because it is not
                 widespread historical practice.

       sourceany The sourceany edit option historically caused ex or vi to
                 source start-up files that were owned by users other than
                 the user running the editor. This option is a security
                 problem, and vendors are strongly encouraged to remove it
                 from their implementations.

       timeout   The timeout edit option historically enabled the (now
                 standard) feature of only waiting for a short period before
                 returning keys that could be part of a macro. This feature
                 was omitted from POSIX.1‐2008 because its behavior is now
                 standard, it is not widely useful, and it was rarely
                 documented.

       verbose   The verbose edit option has been used in some
                 implementations of vi to cause vi to output error messages
                 for common errors; for example, attempting to move the
                 cursor past the beginning or end of the line instead of
                 only alerting the screen. (The historical vi only alerted
                 the terminal and presented no message for such errors. The
                 historical editor option terse did not select when to
                 present error messages, it only made existing error
                 messages more or less verbose.) This option was omitted
                 from POSIX.1‐2008 because it is not widespread historical
                 practice; however, implementors are encouraged to use it if
                 they wish to provide error messages for naive users.

       wraplen   The wraplen edit option has been used in some
                 implementations of vi to specify an automatic margin
                 measured from the left margin instead of from the right
                 margin. This is useful when multiple screen sizes are being
                 used to edit a single file. This option was omitted from
                 POSIX.1‐2008 because it is not widespread historical
                 practice; however, implementors are encouraged to use it if
                 they add this functionality.

   autoindent, ai
       Historically, the command 0a did not do any autoindentation,
       regardless of the current indentation of line 1. POSIX.1‐2008
       requires that any indentation present in line 1 be used.

   autoprint, ap
       Historically, the autoprint edit option was not completely consistent
       or based solely on modifications to the edit buffer. Exceptions were
       the read command (when reading from a file, but not from a filter),
       the append, change, insert, global, and v commands, all of which were
       not affected by autoprint, and the tag command, which was affected by
       autoprint.  POSIX.1‐2008 requires conformance to historical practice.

       Historically, the autoprint option only applied to the last of
       multiple commands entered using <vertical-line> delimiters; for
       example, delete <newline> was affected by autoprint, but
       delete|version <newline> was not. POSIX.1‐2008 requires conformance
       to historical practice.

   autowrite, aw
       Appending the '!'  character to the ex next command to avoid
       performing an automatic write was not supported in historical
       implementations. POSIX.1‐2008 requires that the behavior match the
       other ex commands for consistency.

   ignorecase, ic
       Historical implementations of case-insensitive matching (the
       ignorecase edit option) lead to counter-intuitive situations when
       uppercase characters were used in range expressions. Historically,
       the process was as follows:

        1. Take a line of text from the edit buffer.

        2. Convert uppercase to lowercase in text line.

        3. Convert uppercase to lowercase in regular expressions, except in
           character class specifications.

        4. Match regular expressions against text.

       This would mean that, with ignorecase in effect, the text:

           The cat sat on the mat

       would be matched by

           /^the/

       but not by:

           /^[A−Z]he/

       For consistency with other commands implementing regular expressions,
       POSIX.1‐2008 does not permit this behavior.

   paragraphs, para
       The ISO POSIX‐2:1993 standard made the default paragraphs and
       sections edit options implementation-defined, arguing they were
       historically oriented to the UNIX system troff text formatter, and a
       ``portable user'' could use the {, }, [[, ]], (, and ) commands in
       open or visual mode and have the cursor stop in unexpected places.
       POSIX.1‐2008 specifies their values in the POSIX locale because the
       unusual grouping (they only work when grouped into two characters at
       a time) means that they cannot be used for general-purpose movement,
       regardless.

   readonly
       Implementations are encouraged to provide the best possible
       information to the user as to the read-only status of the file, with
       the exception that they should not consider the current special
       privileges of the process. This provides users with a safety net
       because they must force the overwrite of read-only files, even when
       running with additional privileges.

       The readonly edit option specification largely conforms to historical
       practice. The only difference is that historical implementations did
       not notice that the user had set the readonly edit option in cases
       where the file was already marked read-only for some reason, and
       would therefore reinitialize the readonly edit option the next time
       the contents of the edit buffer were replaced. This behavior is
       disallowed by POSIX.1‐2008.

   report
       The requirement that lines copied to a buffer interact differently
       than deleted lines is historical practice. For example, if the report
       edit option is set to 3, deleting 3 lines will cause a report to be
       written, but 4 lines must be copied before a report is written.

       The requirement that the ex global, v, open, undo, and visual
       commands present reports based on the total number of lines added or
       deleted during the command execution, and that commands executed by
       the global and v commands not present reports, is historical
       practice. POSIX.1‐2008 extends historical practice by requiring that
       buffer execution be treated similarly. The reasons for this are two-
       fold. Historically, only the report by the last command executed from
       the buffer would be seen by the user, as each new report would
       overwrite the last. In addition, the standard developers believed
       that buffer execution had more in common with global and v commands
       than it did with other ex commands, and should behave similarly, for
       consistency and simplicity of specification.

   showmatch, sm
       The length of time the cursor spends on the matching character is
       unspecified because the timing capabilities of systems are often
       inexact and variable. The time should be long enough for the user to
       notice, but not long enough for the user to become annoyed. Some
       implementations of vi have added a matchtime option that permits
       users to set the number of 0,1 second intervals the cursor pauses on
       the matching character.

   showmode
       The showmode option has been used in some historical implementations
       of ex and vi to display the current editing mode when in open or
       visual mode. The editing modes have generally included ``command''
       and ``input'', and sometimes other modes such as ``replace'' and
       ``change''. The string was usually displayed on the bottom line of
       the screen at the far right-hand corner. In addition, a preceding '*'
       character often denoted whether the contents of the edit buffer had
       been modified. The latter display has sometimes been part of the
       showmode option, and sometimes based on another option. This option
       was not available in the 4 BSD historical implementation of vi, but
       was viewed as generally useful, particularly to novice users, and is
       required by POSIX.1‐2008.

       The smd shorthand for the showmode option was not present in all
       historical implementations of the editor.  POSIX.1‐2008 requires it,
       for consistency.

       Not all historical implementations of the editor displayed a mode
       string for command mode, differentiating command mode from text input
       mode by the absence of a mode string. POSIX.1‐2008 permits this
       behavior for consistency with historical practice, but
       implementations are encouraged to provide a display string for both
       modes.

   slowopen
       Historically, the slowopen option was automatically set if the
       terminal baud rate was less than 1200 baud, or if the baud rate was
       1200 baud and the redraw option was not set. The slowopen option had
       two effects. First, when inserting characters in the middle of a
       line, characters after the cursor would not be pushed ahead, but
       would appear to be overwritten. Second, when creating a new line of
       text, lines after the current line would not be scrolled down, but
       would appear to be overwritten. In both cases, ending text input mode
       would cause the screen to be refreshed to match the actual contents
       of the edit buffer. Finally, terminals that were sufficiently
       intelligent caused the editor to ignore the slowopen option.
       POSIX.1‐2008 permits most historical behavior, extending historical
       practice to require slowopen behaviors if the edit option is set by
       the user.

   tags
       The default path for tags files is left unspecified as
       implementations may have their own tags implementations that do not
       correspond to the historical ones. The default tags option value
       should probably at least include the file ./tags.

   term
       Historical implementations of ex and vi ignored changes to the term
       edit option after the initial terminal information was loaded. This
       is permitted by POSIX.1‐2008; however, implementations are encouraged
       to permit the user to modify their terminal type at any time.

   terse
       Historically, the terse edit option optionally provided a shorter,
       less descriptive error message, for some error messages. This is
       permitted, but not required, by POSIX.1‐2008. Historically, most
       common visual mode errors (for example, trying to move the cursor
       past the end of a line) did not result in an error message, but
       simply alerted the terminal. Implementations wishing to provide
       messages for novice users are urged to do so based on the edit option
       verbose, and not terse.

   window
       In historical implementations, the default for the window edit option
       was based on the baud rate as follows:

        1. If the baud rate was less than 1200, the edit option w300 set the
           window value; for example, the line:

               set w300=12

           would set the window option to 12 if the baud rate was less than
           1200.

        2. If the baud rate was equal to 1200, the edit option w1200 set the
           window value.

        3. If the baud rate was greater than 1200, the edit option w9600 set
           the window value.

       The w300, w1200, and w9600 options do not appear in POSIX.1‐2008
       because of their dependence on specific baud rates.

       In historical implementations, the size of the window displayed by
       various commands was related to, but not necessarily the same as, the
       window edit option. For example, the size of the window was set by
       the ex command visual 10, but it did not change the value of the
       window edit option. However, changing the value of the window edit
       option did change the number of lines that were displayed when the
       screen was repainted. POSIX.1‐2008 does not permit this behavior in
       the interests of consistency and simplicity of specification, and
       requires that all commands that change the number of lines that are
       displayed do it by setting the value of the window edit option.

   wrapmargin, wm
       Historically, the wrapmargin option did not affect maps inserting
       characters that also had associated counts; for example
       :map K 5aABC DEF.  Unfortunately, there are widely used maps that
       depend on this behavior.  For consistency and simplicity of
       specification, POSIX.1‐2008 does not permit this behavior.

       Historically, wrapmargin was calculated using the column display
       width of all characters on the screen. For example, an implementation
       using "^I" to represent <tab> characters when the list edit option
       was set, where '^' and 'I' each took up a single column on the
       screen, would calculate the wrapmargin based on a value of 2 for each
       <tab>.  The number edit option similarly changed the effective length
       of the line as well.  POSIX.1‐2008 requires conformance to historical
       practice.

       Earlier versions of this standard allowed for implementations with
       bytes other than eight bits, but this has been modified in this
       version.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.9.1.1, Command Search and Execution, ctags(1p), ed(1p),
       sed(1p), sh(1p), stty(1p), vi(1p)

       The Base Definitions volume of POSIX.1‐2008, Table 5-1, Escape
       Sequences and Associated Actions, Chapter 8, Environment Variables,
       Section 9.3, Basic Regular Expressions, Section 12.2, Utility Syntax
       Guidelines

       The System Interfaces volume of POSIX.1‐2008, access(3p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                              EX(1P)

Pages that refer to this page: ed(1p)more(1p)vi(1p)