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

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

       sh — shell, the standard command language interpreter

SYNOPSIS         top

       sh [−abCefhimnuvx] [−o option]... [+abCefhimnuvx] [+o option]...
           [command_file [argument...]]

       sh −c [−abCefhimnuvx] [−o option]... [+abCefhimnuvx] [+o option]...
           command_string [command_name [argument...]]

       sh −s [−abCefhimnuvx] [−o option]... [+abCefhimnuvx] [+o option]...
           [argument...]

DESCRIPTION         top

       The sh utility is a command language interpreter that shall execute
       commands read from a command line string, the standard input, or a
       specified file. The application shall ensure that the commands to be
       executed are expressed in the language described in Chapter 2, Shell
       Command Language.

       Pathname expansion shall not fail due to the size of a file.

       Shell input and output redirections have an implementation-defined
       offset maximum that is established in the open file description.

OPTIONS         top

       The sh utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines, with an
       extension for support of a leading <plus-sign> ('+') as noted below.

       The −a, −b, −C, −e, −f, −m, −n, −o option, −u, −v, and −x options are
       described as part of the set utility in Section 2.14, Special Built-
       In Utilities.  The option letters derived from the set special built-
       in shall also be accepted with a leading <plus-sign> ('+') instead of
       a leading <hyphen> (meaning the reverse case of the option as
       described in this volume of POSIX.1‐2008).

       The following additional options shall be supported:

       −c        Read commands from the command_string operand. Set the
                 value of special parameter 0 (see Section 2.5.2, Special
                 Parameters) from the value of the command_name operand and
                 the positional parameters ($1, $2, and so on) in sequence
                 from the remaining argument operands. No commands shall be
                 read from the standard input.

       −i        Specify that the shell is interactive; see below. An
                 implementation may treat specifying the −i option as an
                 error if the real user ID of the calling process does not
                 equal the effective user ID or if the real group ID does
                 not equal the effective group ID.

       −s        Read commands from the standard input.

       If there are no operands and the −c option is not specified, the −s
       option shall be assumed.

       If the −i option is present, or if there are no operands and the
       shell's standard input and standard error are attached to a terminal,
       the shell is considered to be interactive.

OPERANDS         top

       The following operands shall be supported:

       −         A single <hyphen> shall be treated as the first operand and
                 then ignored. If both '−' and "−−" are given as arguments,
                 or if other operands precede the single <hyphen>, the
                 results are undefined.

       argument  The positional parameters ($1, $2, and so on) shall be set
                 to arguments, if any.

       command_file
                 The pathname of a file containing commands. If the pathname
                 contains one or more <slash> characters, the implementation
                 attempts to read that file; the file need not be
                 executable. If the pathname does not contain a <slash>
                 character:

                  *  The implementation shall attempt to read that file from
                     the current working directory; the file need not be
                     executable.

                  *  If the file is not in the current working directory,
                     the implementation may perform a search for an
                     executable file using the value of PATH, as described
                     in Section 2.9.1.1, Command Search and Execution.

                 Special parameter 0 (see Section 2.5.2, Special Parameters)
                 shall be set to the value of command_file.  If sh is called
                 using a synopsis form that omits command_file, special
                 parameter 0 shall be set to the value of the first argument
                 passed to sh from its parent (for example, argv[0] for a C
                 program), which is normally a pathname used to execute the
                 sh utility.

       command_name
                 A string assigned to special parameter 0 when executing the
                 commands in command_string.  If command_name is not
                 specified, special parameter 0 shall be set to the value of
                 the first argument passed to sh from its parent (for
                 example, argv[0] for a C program), which is normally a
                 pathname used to execute the sh utility.

       command_string
                 A string that shall be interpreted by the shell as one or
                 more commands, as if the string were the argument to the
                 system() function defined in the System Interfaces volume
                 of POSIX.1‐2008. If the command_string operand is an empty
                 string, sh shall exit with a zero exit status.

STDIN         top

       The standard input shall be used only if one of the following is
       true:

        *  The −s option is specified.

        *  The −c option is not specified and no operands are specified.

        *  The script executes one or more commands that require input from
           standard input (such as a read command that does not redirect its
           input).

       See the INPUT FILES section.

       When the shell is using standard input and it invokes a command that
       also uses standard input, the shell shall ensure that the standard
       input file pointer points directly after the command it has read when
       the command begins execution. It shall not read ahead in such a
       manner that any characters intended to be read by the invoked command
       are consumed by the shell (whether interpreted by the shell or not)
       or that characters that are not read by the invoked command are not
       seen by the shell. When the command expecting to read standard input
       is started asynchronously by an interactive shell, it is unspecified
       whether characters are read by the command or interpreted by the
       shell.

       If the standard input to sh is a FIFO or terminal device and is set
       to non-blocking reads, then sh shall enable blocking reads on
       standard input. This shall remain in effect when the command
       completes.

INPUT FILES         top

       The input file shall be a text file, except that line lengths shall
       be unlimited. If the input file is empty or consists solely of blank
       lines or comments, or both, sh shall exit with a zero exit status.

ENVIRONMENT VARIABLES         top

       The following environment variables shall affect the execution of sh:

       ENV       This variable, when and only when an interactive shell is
                 invoked, shall be subjected to parameter expansion (see
                 Section 2.6.2, Parameter Expansion) by the shell, and the
                 resulting value shall be used as a pathname of a file
                 containing shell commands to execute in the current
                 environment.  The file need not be executable. If the
                 expanded value of ENV is not an absolute pathname, the
                 results are unspecified.  ENV shall be ignored if the real
                 and effective user IDs or real and effective group IDs of
                 the process are different.

       FCEDIT    This variable, when expanded by the shell, shall determine
                 the default value for the −e editor option's editor option-
                 argument. If FCEDIT is null or unset, ed shall be used as
                 the editor.

       HISTFILE  Determine a pathname naming a command history file. If the
                 HISTFILE variable is not set, the shell may attempt to
                 access or create a file .sh_history in the directory
                 referred to by the HOME environment variable. If the shell
                 cannot obtain both read and write access to, or create, the
                 history file, it shall use an unspecified mechanism that
                 allows the history to operate properly.  (References to
                 history ``file'' in this section shall be understood to
                 mean this unspecified mechanism in such cases.) An
                 implementation may choose to access this variable only when
                 initializing the history file; this initialization shall
                 occur when fc or sh first attempt to retrieve entries from,
                 or add entries to, the file, as the result of commands
                 issued by the user, the file named by the ENV variable, or
                 implementation-defined system start-up files.
                 Implementations may choose to disable the history list
                 mechanism for users with appropriate privileges who do not
                 set HISTFILE; the specific circumstances under which this
                 occurs are implementation-defined. If more than one
                 instance of the shell is using the same history file, it is
                 unspecified how updates to the history file from those
                 shells interact. As entries are deleted from the history
                 file, they shall be deleted oldest first. It is unspecified
                 when history file entries are physically removed from the
                 history file.

       HISTSIZE  Determine a decimal number representing the limit to the
                 number of previous commands that are accessible. If this
                 variable is unset, an unspecified default greater than or
                 equal to 128 shall be used. The maximum number of commands
                 in the history list is unspecified, but shall be at least
                 128. An implementation may choose to access this variable
                 only when initializing the history file, as described under
                 HISTFILE.  Therefore, it is unspecified whether changes
                 made to HISTSIZE after the history file has been
                 initialized are effective.

       HOME      Determine the pathname of the user's home directory. The
                 contents of HOME are used in tilde expansion as described
                 in Section 2.6.1, Tilde Expansion.

       IFS       A string treated as a list of characters that is used for
                 field splitting and to split lines into fields with the
                 read command.

                 If IFS is not set, it shall behave as normal for an unset
                 variable, except that field splitting by the shell and line
                 splitting by the read command shall be performed as if the
                 value of IFS is <space><tab><newline>; see Section 2.6.5,
                 Field Splitting.

                 Implementations may ignore the value of IFS in the
                 environment, or the absence of IFS from the environment, at
                 the time the shell is invoked, in which case the shell
                 shall set IFS to <space><tab><newline> when it is invoked.

       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 behavior of range expressions, equivalence
                 classes, and multi-character collating elements within
                 pattern matching.

       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), which characters are defined as letters (character
                 class alpha), and the behavior of character classes within
                 pattern matching.

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

       MAIL      Determine a pathname of the user's mailbox file for
                 purposes of incoming mail notification. If this variable is
                 set, the shell shall inform the user if the file named by
                 the variable is created or if its modification time has
                 changed. Informing the user shall be accomplished by
                 writing a string of unspecified format to standard error
                 prior to the writing of the next primary prompt string.
                 Such check shall be performed only after the completion of
                 the interval defined by the MAILCHECK variable after the
                 last such check. The user shall be informed only if MAIL is
                 set and MAILPATH is not set.

       MAILCHECK
                 Establish a decimal integer value that specifies how often
                 (in seconds) the shell shall check for the arrival of mail
                 in the files specified by the MAILPATH or MAIL variables.
                 The default value shall be 600 seconds. If set to zero, the
                 shell shall check before issuing each primary prompt.

       MAILPATH  Provide a list of pathnames and optional messages separated
                 by <colon> characters. If this variable is set, the shell
                 shall inform the user if any of the files named by the
                 variable are created or if any of their modification times
                 change. (See the preceding entry for MAIL for descriptions
                 of mail arrival and user informing.) Each pathname can be
                 followed by '%' and a string that shall be subjected to
                 parameter expansion and written to standard error when the
                 modification time changes. If a '%' character in the
                 pathname is preceded by a <backslash>, it shall be treated
                 as a literal '%' in the pathname. The default message is
                 unspecified.

                 The MAILPATH environment variable takes precedence over the
                 MAIL variable.

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

       PATH      Establish a string formatted as described in the Base
                 Definitions volume of POSIX.1‐2008, Chapter 8, Environment
                 Variables, used to effect command interpretation; see
                 Section 2.9.1.1, Command Search and Execution.

       PWD       This variable shall represent an absolute pathname of the
                 current working directory. Assignments to this variable may
                 be ignored.

ASYNCHRONOUS EVENTS         top

       The sh utility shall take the standard action for all signals (see
       Section 1.4, Utility Description Defaults) with the following
       exceptions.

       If the shell is interactive, SIGINT signals received during command
       line editing shall be handled as described in the EXTENDED
       DESCRIPTION, and SIGINT signals received at other times shall be
       caught but no action performed.

       If the shell is interactive:

        *  SIGQUIT and SIGTERM signals shall be ignored.

        *  If the −m option is in effect, SIGTTIN, SIGTTOU, and SIGTSTP
           signals shall be ignored.

        *  If the −m option is not in effect, it is unspecified whether
           SIGTTIN, SIGTTOU, and SIGTSTP signals are ignored, set to the
           default action, or caught.  If they are caught, the shell shall,
           in the signal-catching function, set the signal to the default
           action and raise the signal (after taking any appropriate steps,
           such as restoring terminal settings).

       The standard actions, and the actions described above for interactive
       shells, can be overridden by use of the trap special built-in utility
       (see trap(1p) and Section 2.11, Signals and Error Handling).

STDOUT         top

       See the STDERR section.

STDERR         top

       Except as otherwise stated (by the descriptions of any invoked
       utilities or in interactive mode), standard error shall be used only
       for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       See Chapter 2, Shell Command Language.  The functionality described
       in the rest of the EXTENDED DESCRIPTION section shall be provided on
       implementations that support the User Portability Utilities option
       (and the rest of this section is not further shaded for this option).

   Command History List
       When the sh utility is being used interactively, it shall maintain a
       list of commands previously entered from the terminal in the file
       named by the HISTFILE environment variable. The type, size, and
       internal format of this file are unspecified. Multiple sh processes
       can share access to the file for a user, if file access permissions
       allow this; see the description of the HISTFILE environment variable.

   Command Line Editing
       When sh is being used interactively from a terminal, the current
       command and the command history (see fc(1p)) can be edited using vi-
       mode command line editing. This mode uses commands, described below,
       similar to a subset of those described in the vi utility.
       Implementations may offer other command line editing modes
       corresponding to other editing utilities.

       The command set −o vi shall enable vi-mode editing and place sh into
       vi insert mode (see Command Line Editing (vi-mode)).  This command
       also shall disable any other editing mode that the implementation may
       provide. The command set +o vi disables vi-mode editing.

       Certain block-mode terminals may be unable to support shell command
       line editing. If a terminal is unable to provide either edit mode, it
       need not be possible to set −o vi when using the shell on this
       terminal.

       In the following sections, the characters erase, interrupt, kill, and
       end-of-file are those set by the stty utility.

   Command Line Editing (vi-mode)
       In vi editing mode, there shall be a distinguished line, the edit
       line. All the editing operations which modify a line affect the edit
       line. The edit line is always the newest line in the command history
       buffer.

       With vi-mode enabled, sh can be switched between insert mode and
       command mode.

       When in insert mode, an entered character shall be inserted into the
       command line, except as noted in vi Line Editing Insert Mode.  Upon
       entering sh and after termination of the previous command, sh shall
       be in insert mode.

       Typing an escape character shall switch sh into command mode (see vi
       Line Editing Command Mode).  In command mode, an entered character
       shall either invoke a defined operation, be used as part of a multi-
       character operation, or be treated as an error. A character that is
       not recognized as part of an editing command shall terminate any
       specific editing command and shall alert the terminal. If sh receives
       a SIGINT signal in command mode (whether generated by typing the
       interrupt character or by other means), it shall terminate command
       line editing on the current command line, reissue the prompt on the
       next line of the terminal, and reset the command history (see fc(1p))
       so that the most recently executed command is the previous command
       (that is, the command that was being edited when it was interrupted
       is not re-entered into the history).

       In the following sections, the phrase ``move the cursor to the
       beginning of the word'' shall mean ``move the cursor to the first
       character of the current word'' and the phrase ``move the cursor to
       the end of the word'' shall mean ``move the cursor to the last
       character of the current word''. The phrase ``beginning of the
       command line'' indicates the point between the end of the prompt
       string issued by the shell (or the beginning of the terminal line, if
       there is no prompt string) and the first character of the command
       text.

   vi Line Editing Insert Mode
       While in insert mode, any character typed shall be inserted in the
       current command line, unless it is from the following set.

       <newline> Execute the current command line. If the current command
                 line is not empty, this line shall be entered into the
                 command history (see fc(1p)).

       erase     Delete the character previous to the current cursor
                 position and move the current cursor position back one
                 character. In insert mode, characters shall be erased from
                 both the screen and the buffer when backspacing.

       interrupt If sh receives a SIGINT signal in insert mode (whether
                 generated by typing the interrupt character or by other
                 means), it shall terminate command line editing with the
                 same effects as described for interrupting command mode;
                 see Command Line Editing (vi-mode).

       kill      Clear all the characters from the input line.

       <control>‐V
                 Insert the next character input, even if the character is
                 otherwise a special insert mode character.

       <control>‐W
                 Delete the characters from the one preceding the cursor to
                 the preceding word boundary. The word boundary in this case
                 is the closer to the cursor of either the beginning of the
                 line or a character that is in neither the blank nor punct
                 character classification of the current locale.

       end-of-file
                 Interpreted as the end of input in sh.  This interpretation
                 shall occur only at the beginning of an input line. If end-
                 of-file is entered other than at the beginning of the line,
                 the results are unspecified.

       <ESC>     Place sh into command mode.

   vi Line Editing Command Mode
       In command mode for the command line editing feature, decimal digits
       not beginning with 0 that precede a command letter shall be
       remembered. Some commands use these decimal digits as a count number
       that affects the operation.

       The term motion command represents one of the commands:

           <space>  0  b  F  l  W  ^  $  ;  E  f  T  w  |  ,  B  e  h  t

       If the current line is not the edit line, any command that modifies
       the current line shall cause the content of the current line to
       replace the content of the edit line, and the current line shall
       become the edit line. This replacement cannot be undone (see the u
       and U commands below). The modification requested shall then be
       performed to the edit line. When the current line is the edit line,
       the modification shall be done directly to the edit line.

       Any command that is preceded by count shall take a count (the numeric
       value of any preceding decimal digits). Unless otherwise noted, this
       count shall cause the specified operation to repeat by the number of
       times specified by the count.  Also unless otherwise noted, a count
       that is out of range is considered an error condition and shall alert
       the terminal, but neither the cursor position, nor the command line,
       shall change.

       The terms word and bigword are used as defined in the vi description.
       The term save buffer corresponds to the term unnamed buffer in vi.

       The following commands shall be recognized in command mode:

       <newline> Execute the current command line. If the current command
                 line is not empty, this line shall be entered into the
                 command history (see fc(1p)).

       <control>‐L
                 Redraw the current command line. Position the cursor at the
                 same location on the redrawn line.

       #         Insert the character '#' at the beginning of the current
                 command line and treat the resulting edit line as a
                 comment. This line shall be entered into the command
                 history; see fc(1p).

       =         Display the possible shell word expansions (see Section
                 2.6, Word Expansions) of the bigword at the current command
                 line position.

                 Note:     This does not modify the content of the current
                           line, and therefore does not cause the current
                           line to become the edit line.

                 These expansions shall be displayed on subsequent terminal
                 lines. If the bigword contains none of the characters '?',
                 '*', or '[', an <asterisk> ('*') shall be implicitly
                 assumed at the end. If any directories are matched, these
                 expansions shall have a '/' character appended. After the
                 expansion, the line shall be redrawn, the cursor
                 repositioned at the current cursor position, and sh shall
                 be placed in command mode.

       \         Perform pathname expansion (see Section 2.6.6, Pathname
                 Expansion) on the current bigword, up to the largest set of
                 characters that can be matched uniquely. If the bigword
                 contains none of the characters '?', '*', or '[', an
                 <asterisk> ('*') shall be implicitly assumed at the end.
                 This maximal expansion then shall replace the original
                 bigword in the command line, and the cursor shall be placed
                 after this expansion. If the resulting bigword completely
                 and uniquely matches a directory, a '/' character shall be
                 inserted directly after the bigword. If some other file is
                 completely matched, a single <space> shall be inserted
                 after the bigword. After this operation, sh shall be placed
                 in insert mode.

       *         Perform pathname expansion on the current bigword and
                 insert all expansions into the command to replace the
                 current bigword, with each expansion separated by a single
                 <space>.  If at the end of the line, the current cursor
                 position shall be moved to the first column position
                 following the expansions and sh shall be placed in insert
                 mode. Otherwise, the current cursor position shall be the
                 last column position of the first character after the
                 expansions and sh shall be placed in insert mode. If the
                 current bigword contains none of the characters '?', '*',
                 or '[', before the operation, an <asterisk> ('*') shall be
                 implicitly assumed at the end.

       @letter   Insert the value of the alias named _letter.  The symbol
                 letter represents a single alphabetic character from the
                 portable character set; implementations may support
                 additional characters as an extension. If the alias _letter
                 contains other editing commands, these commands shall be
                 performed as part of the insertion. If no alias _letter is
                 enabled, this command shall have no effect.

       [count]~  Convert, if the current character is a lowercase letter, to
                 the equivalent uppercase letter and vice versa, as
                 prescribed by the current locale. The current cursor
                 position then shall be advanced by one character. If the
                 cursor was positioned on the last character of the line,
                 the case conversion shall occur, but the cursor shall not
                 advance. If the '~' command is preceded by a count, that
                 number of characters shall be converted, and the cursor
                 shall be advanced to the character position after the last
                 character converted.  If the count is larger than the
                 number of characters after the cursor, this shall not be
                 considered an error; the cursor shall advance to the last
                 character on the line.

       [count].  Repeat the most recent non-motion command, even if it was
                 executed on an earlier command line. If the previous
                 command was preceded by a count, and no count is given on
                 the '.'  command, the count from the previous command shall
                 be included as part of the repeated command. If the '.'
                 command is preceded by a count, this shall override any
                 count argument to the previous command. The count specified
                 in the '.'  command shall become the count for subsequent
                 '.'  commands issued without a count.

       [number]v Invoke the vi editor to edit the current command line in a
                 temporary file. When the editor exits, the commands in the
                 temporary file shall be executed and placed in the command
                 history. If a number is included, it specifies the command
                 number in the command history to be edited, rather than the
                 current command line.

       [count]l   (ell)

       [count]<space>
                 Move the current cursor position to the next character
                 position. If the cursor was positioned on the last
                 character of the line, the terminal shall be alerted and
                 the cursor shall not be advanced. If the count is larger
                 than the number of characters after the cursor, this shall
                 not be considered an error; the cursor shall advance to the
                 last character on the line.

       [count]h  Move the current cursor position to the countth (default 1)
                 previous character position. If the cursor was positioned
                 on the first character of the line, the terminal shall be
                 alerted and the cursor shall not be moved. If the count is
                 larger than the number of characters before the cursor,
                 this shall not be considered an error; the cursor shall
                 move to the first character on the line.

       [count]w  Move to the start of the next word. If the cursor was
                 positioned on the last character of the line, the terminal
                 shall be alerted and the cursor shall not be advanced. If
                 the count is larger than the number of words after the
                 cursor, this shall not be considered an error; the cursor
                 shall advance to the last character on the line.

       [count]W  Move to the start of the next bigword. If the cursor was
                 positioned on the last character of the line, the terminal
                 shall be alerted and the cursor shall not be advanced. If
                 the count is larger than the number of bigwords after the
                 cursor, this shall not be considered an error; the cursor
                 shall advance to the last character on the line.

       [count]e  Move to the end of the current word. If at the end of a
                 word, move to the end of the next word. If the cursor was
                 positioned on the last character of the line, the terminal
                 shall be alerted and the cursor shall not be advanced. If
                 the count is larger than the number of words after the
                 cursor, this shall not be considered an error; the cursor
                 shall advance to the last character on the line.

       [count]E  Move to the end of the current bigword. If at the end of a
                 bigword, move to the end of the next bigword. If the cursor
                 was positioned on the last character of the line, the
                 terminal shall be alerted and the cursor shall not be
                 advanced. If the count is larger than the number of
                 bigwords after the cursor, this shall not be considered an
                 error; the cursor shall advance to the last character on
                 the line.

       [count]b  Move to the beginning of the current word. If at the
                 beginning of a word, move to the beginning of the previous
                 word. If the cursor was positioned on the first character
                 of the line, the terminal shall be alerted and the cursor
                 shall not be moved. If the count is larger than the number
                 of words preceding the cursor, this shall not be considered
                 an error; the cursor shall return to the first character on
                 the line.

       [count]B  Move to the beginning of the current bigword. If at the
                 beginning of a bigword, move to the beginning of the
                 previous bigword. If the cursor was positioned on the first
                 character of the line, the terminal shall be alerted and
                 the cursor shall not be moved. If the count is larger than
                 the number of bigwords preceding the cursor, this shall not
                 be considered an error; the cursor shall return to the
                 first character on the line.

       ^         Move the current cursor position to the first character on
                 the input line that is not a <blank>.

       $         Move to the last character position on the current command
                 line.

       0         (Zero.) Move to the first character position on the current
                 command line.

       [count]|  Move to the countth character position on the current
                 command line. If no number is specified, move to the first
                 position. The first character position shall be numbered 1.
                 If the count is larger than the number of characters on the
                 line, this shall not be considered an error; the cursor
                 shall be placed on the last character on the line.

       [count]fc Move to the first occurrence of the character 'c' that
                 occurs after the current cursor position. If the cursor was
                 positioned on the last character of the line, the terminal
                 shall be alerted and the cursor shall not be advanced. If
                 the character 'c' does not occur in the line after the
                 current cursor position, the terminal shall be alerted and
                 the cursor shall not be moved.

       [count]Fc Move to the first occurrence of the character 'c' that
                 occurs before the current cursor position. If the cursor
                 was positioned on the first character of the line, the
                 terminal shall be alerted and the cursor shall not be
                 moved. If the character 'c' does not occur in the line
                 before the current cursor position, the terminal shall be
                 alerted and the cursor shall not be moved.

       [count]tc Move to the character before the first occurrence of the
                 character 'c' that occurs after the current cursor
                 position. If the cursor was positioned on the last
                 character of the line, the terminal shall be alerted and
                 the cursor shall not be advanced. If the character 'c' does
                 not occur in the line after the current cursor position,
                 the terminal shall be alerted and the cursor shall not be
                 moved.

       [count]Tc Move to the character after the first occurrence of the
                 character 'c' that occurs before the current cursor
                 position. If the cursor was positioned on the first
                 character of the line, the terminal shall be alerted and
                 the cursor shall not be moved. If the character 'c' does
                 not occur in the line before the current cursor position,
                 the terminal shall be alerted and the cursor shall not be
                 moved.

       [count];  Repeat the most recent f, F, t, or T command. Any number
                 argument on that previous command shall be ignored. Errors
                 are those described for the repeated command.

       [count],  Repeat the most recent f, F, t, or T command. Any number
                 argument on that previous command shall be ignored.
                 However, reverse the direction of that command.

       a         Enter insert mode after the current cursor position.
                 Characters that are entered shall be inserted before the
                 next character.

       A         Enter insert mode after the end of the current command
                 line.

       i         Enter insert mode at the current cursor position.
                 Characters that are entered shall be inserted before the
                 current character.

       I         Enter insert mode at the beginning of the current command
                 line.

       R         Enter insert mode, replacing characters from the command
                 line beginning at the current cursor position.

       [count]cmotion
                 Delete the characters between the current cursor position
                 and the cursor position that would result from the
                 specified motion command. Then enter insert mode before the
                 first character following any deleted characters. If count
                 is specified, it shall be applied to the motion command. A
                 count shall be ignored for the following motion commands:

                     0    ^    $    c

                 If the motion command is the character 'c', the current
                 command line shall be cleared and insert mode shall be
                 entered. If the motion command would move the current
                 cursor position toward the beginning of the command line,
                 the character under the current cursor position shall not
                 be deleted. If the motion command would move the current
                 cursor position toward the end of the command line, the
                 character under the current cursor position shall be
                 deleted.  If the count is larger than the number of
                 characters between the current cursor position and the end
                 of the command line toward which the motion command would
                 move the cursor, this shall not be considered an error; all
                 of the remaining characters in the aforementioned range
                 shall be deleted and insert mode shall be entered. If the
                 motion command is invalid, the terminal shall be alerted,
                 the cursor shall not be moved, and no text shall be
                 deleted.

       C         Delete from the current character to the end of the line
                 and enter insert mode at the new end-of-line.

       S         Clear the entire edit line and enter insert mode.

       [count]rc Replace the current character with the character 'c'.  With
                 a number count, replace the current and the following
                 count−1 characters. After this command, the current cursor
                 position shall be on the last character that was changed.
                 If the count is larger than the number of characters after
                 the cursor, this shall not be considered an error; all of
                 the remaining characters shall be changed.

       [count]_  Append a <space> after the current character position and
                 then append the last bigword in the previous input line
                 after the <space>.  Then enter insert mode after the last
                 character just appended. With a number count, append the
                 countth bigword in the previous line.

       [count]x  Delete the character at the current cursor position and
                 place the deleted characters in the save buffer. If the
                 cursor was positioned on the last character of the line,
                 the character shall be deleted and the cursor position
                 shall be moved to the previous character (the new last
                 character). If the count is larger than the number of
                 characters after the cursor, this shall not be considered
                 an error; all the characters from the cursor to the end of
                 the line shall be deleted.

       [count]X  Delete the character before the current cursor position and
                 place the deleted characters in the save buffer. The
                 character under the current cursor position shall not
                 change. If the cursor was positioned on the first character
                 of the line, the terminal shall be alerted, and the X
                 command shall have no effect. If the line contained a
                 single character, the X command shall have no effect. If
                 the line contained no characters, the terminal shall be
                 alerted and the cursor shall not be moved. If the count is
                 larger than the number of characters before the cursor,
                 this shall not be considered an error; all the characters
                 from before the cursor to the beginning of the line shall
                 be deleted.

       [count]dmotion
                 Delete the characters between the current cursor position
                 and the character position that would result from the
                 motion command. A number count repeats the motion command
                 count times. If the motion command would move toward the
                 beginning of the command line, the character under the
                 current cursor position shall not be deleted. If the motion
                 command is d, the entire current command line shall be
                 cleared. If the count is larger than the number of
                 characters between the current cursor position and the end
                 of the command line toward which the motion command would
                 move the cursor, this shall not be considered an error; all
                 of the remaining characters in the aforementioned range
                 shall be deleted. The deleted characters shall be placed in
                 the save buffer.

       D         Delete all characters from the current cursor position to
                 the end of the line. The deleted characters shall be placed
                 in the save buffer.

       [count]ymotion
                 Yank (that is, copy) the characters from the current cursor
                 position to the position resulting from the motion command
                 into the save buffer. A number count shall be applied to
                 the motion command. If the motion command would move toward
                 the beginning of the command line, the character under the
                 current cursor position shall not be included in the set of
                 yanked characters. If the motion command is y, the entire
                 current command line shall be yanked into the save buffer.
                 The current cursor position shall be unchanged. If the
                 count is larger than the number of characters between the
                 current cursor position and the end of the command line
                 toward which the motion command would move the cursor, this
                 shall not be considered an error; all of the remaining
                 characters in the aforementioned range shall be yanked.

       Y         Yank the characters from the current cursor position to the
                 end of the line into the save buffer. The current character
                 position shall be unchanged.

       [count]p  Put a copy of the current contents of the save buffer after
                 the current cursor position. The current cursor position
                 shall be advanced to the last character put from the save
                 buffer. A count shall indicate how many copies of the save
                 buffer shall be put.

       [count]P  Put a copy of the current contents of the save buffer
                 before the current cursor position. The current cursor
                 position shall be moved to the last character put from the
                 save buffer. A count shall indicate how many copies of the
                 save buffer shall be put.

       u         Undo the last command that changed the edit line. This
                 operation shall not undo the copy of any command line to
                 the edit line.

       U         Undo all changes made to the edit line. This operation
                 shall not undo the copy of any command line to the edit
                 line.

       [count]k

       [count]−  Set the current command line to be the countth previous
                 command line in the shell command history. If count is not
                 specified, it shall default to 1. The cursor shall be
                 positioned on the first character of the new command. If a
                 k or command would retreat past the maximum number of
                 commands in effect for this shell (affected by the HISTSIZE
                 environment variable), the terminal shall be alerted, and
                 the command shall have no effect.

       [count]j

       [count]+  Set the current command line to be the countth next command
                 line in the shell command history. If count is not
                 specified, it shall default to 1. The cursor shall be
                 positioned on the first character of the new command. If a
                 j or + command advances past the edit line, the current
                 command line shall be restored to the edit line and the
                 terminal shall be alerted.

       [number]G Set the current command line to be the oldest command line
                 stored in the shell command history. With a number number,
                 set the current command line to be the command line number
                 in the history. If command line number does not exist, the
                 terminal shall be alerted and the command line shall not be
                 changed.

       /pattern<newline>
                 Move backwards through the command history, searching for
                 the specified pattern, beginning with the previous command
                 line. Patterns use the pattern matching notation described
                 in Section 2.13, Pattern Matching Notation, except that the
                 '^' character shall have special meaning when it appears as
                 the first character of pattern.  In this case, the '^' is
                 discarded and the characters after the '^' shall be matched
                 only at the beginning of a line. Commands in the command
                 history shall be treated as strings, not as filenames. If
                 the pattern is not found, the current command line shall be
                 unchanged and the terminal is alerted. If it is found in a
                 previous line, the current command line shall be set to
                 that line and the cursor shall be set to the first
                 character of the new command line.

                 If pattern is empty, the last non-empty pattern provided to
                 / or ?  shall be used. If there is no previous non-empty
                 pattern, the terminal shall be alerted and the current
                 command line shall remain unchanged.

       ?pattern<newline>
                 Move forwards through the command history, searching for
                 the specified pattern, beginning with the next command
                 line. Patterns use the pattern matching notation described
                 in Section 2.13, Pattern Matching Notation, except that the
                 '^' character shall have special meaning when it appears as
                 the first character of pattern.  In this case, the '^' is
                 discarded and the characters after the '^' shall be matched
                 only at the beginning of a line. Commands in the command
                 history shall be treated as strings, not as filenames. If
                 the pattern is not found, the current command line shall be
                 unchanged and the terminal alerted. If it is found in a
                 following line, the current command line shall be set to
                 that line and the cursor shall be set to the fist character
                 of the new command line.

                 If pattern is empty, the last non-empty pattern provided to
                 / or ?  shall be used. If there is no previous non-empty
                 pattern, the terminal shall be alerted and the current
                 command line shall remain unchanged.

       n         Repeat the most recent / or ?  command. If there is no
                 previous / or ?, the terminal shall be alerted and the
                 current command line shall remain unchanged.

       N         Repeat the most recent / or ?  command, reversing the
                 direction of the search. If there is no previous / or ?,
                 the terminal shall be alerted and the current command line
                 shall remain unchanged.

EXIT STATUS         top

       The following exit values shall be returned:

           0   The script to be executed consisted solely of zero or more
               blank lines or comments, or both.

       1‐125   A non-interactive shell detected an error other than
               command_file not found, including but not limited to syntax,
               redirection, or variable assignment errors.

         127   A specified command_file could not be found by a non-
               interactive shell.

       Otherwise, the shell shall return the exit status of the last command
       it invoked or attempted to invoke (see also the exit utility in
       Section 2.14, Special Built-In Utilities).

CONSEQUENCES OF ERRORS         top

       See Section 2.8.1, Consequences of Shell Errors.

       The following sections are informative.

APPLICATION USAGE         top

       Standard input and standard error are the files that determine
       whether a shell is interactive when −i is not specified. For example:

           sh > file

       and:

           sh 2> file

       create interactive and non-interactive shells, respectively. Although
       both accept terminal input, the results of error conditions are
       different, as described in Section 2.8.1, Consequences of Shell
       Errors; in the second example a redirection error encountered by a
       special built-in utility aborts the shell.

       A conforming application must protect its first operand, if it starts
       with a <plus-sign>, by preceding it with the "−−" argument that
       denotes the end of the options.

       Applications should note that the standard PATH to the shell cannot
       be assumed to be either /bin/sh or /usr/bin/sh, and should be
       determined by interrogation of the PATH returned by getconf PATH,
       ensuring that the returned pathname is an absolute pathname and not a
       shell built-in.

       For example, to determine the location of the standard sh utility:

           command −v sh

       On some implementations this might return:

           /usr/xpg4/bin/sh

       Furthermore, on systems that support executable scripts (the "#!"
       construct), it is recommended that applications using executable
       scripts install them using getconf PATH to determine the shell
       pathname and update the "#!" script appropriately as it is being
       installed (for example, with sed).  For example:

           #
           # Installation time script to install correct POSIX shell pathname
           #
           # Get list of paths to check
           #
           Sifs=$IFS
           Sifs_set=${IFS+y}
           IFS=:
           set −− $(getconf PATH)
           if [ "$Sifs_set" = y ]
           then
               IFS=$Sifs
           else
               unset IFS
           fi
           #
           # Check each path for 'sh'
           #
           for i
           do
               if [ −x "${i}"/sh ]
               then
                   Pshell=${i}/sh
               fi
           done
           #
           # This is the list of scripts to update. They should be of the
           # form '${name}.source' and will be transformed to '${name}'.
           # Each script should begin:
           #
           # #!INSTALLSHELLPATH
           #
           scripts="a b c"
           #
           # Transform each script
           #
           for i in ${scripts}
           do
               sed −e "s|INSTALLSHELLPATH|${Pshell}|" < ${i}.source > ${i}
           done

EXAMPLES         top

        1. Execute a shell command from a string:

               sh −c "cat myfile"

        2. Execute a shell script from a file in the current directory:

               sh my_shell_cmds

RATIONALE         top

       The sh utility and the set special built-in utility share a common
       set of options.

       The name IFS was originally an abbreviation of ``Input Field
       Separators''; however, this name is misleading as the IFS characters
       are actually used as field terminators. The KornShell ignores the
       contents of IFS upon entry to the script. A conforming application
       cannot rely on importing IFS.  One justification for this, beyond
       security considerations, is to assist possible future shell
       compilers. Allowing IFS to be imported from the environment prevents
       many optimizations that might otherwise be performed via dataflow
       analysis of the script itself.

       The text in the STDIN section about non-blocking reads concerns an
       instance of sh that has been invoked, probably by a C-language
       program, with standard input that has been opened using the
       O_NONBLOCK flag; see open() in the System Interfaces volume of
       POSIX.1‐2008. If the shell did not reset this flag, it would
       immediately terminate because no input data would be available yet
       and that would be considered the same as end-of-file.

       The options associated with a restricted shell (command name rsh and
       the −r option) were excluded because the standard developers
       considered that the implied level of security could not be achieved
       and they did not want to raise false expectations.

       On systems that support set-user-ID scripts, a historical trapdoor
       has been to link a script to the name −i.  When it is called by a
       sequence such as:

           sh −

       or by:

           #! usr/bin/sh −

       the historical systems have assumed that no option letters follow.
       Thus, this volume of POSIX.1‐2008 allows the single <hyphen> to mark
       the end of the options, in addition to the use of the regular "−−"
       argument, because it was considered that the older practice was so
       pervasive. An alternative approach is taken by the KornShell, where
       real and effective user/group IDs must match for an interactive
       shell; this behavior is specifically allowed by this volume of
       POSIX.1‐2008.

       Note:     There are other problems with set-user-ID scripts that the
                 two approaches described here do not resolve.

       The initialization process for the history file can be dependent on
       the system start-up files, in that they may contain commands that
       effectively preempt the user's settings of HISTFILE and HISTSIZE.
       For example, function definition commands are recorded in the history
       file, unless the set −o nolog option is set. If the system
       administrator includes function definitions in some system start-up
       file called before the ENV file, the history file is initialized
       before the user gets a chance to influence its characteristics. In
       some historical shells, the history file is initialized just after
       the ENV file has been processed. Therefore, it is implementation-
       defined whether changes made to HISTFILE after the history file has
       been initialized are effective.

       The default messages for the various MAIL-related messages are
       unspecified because they vary across implementations.  Typical
       messages are:

           "you have mail\n"

       or:

           "you have new mail\n"

       It is important that the descriptions of command line editing refer
       to the same shell as that in POSIX.1‐2008 so that interactive users
       can also be application programmers without having to deal with
       programmatic differences in their two environments. It is also
       essential that the utility name sh be specified because this explicit
       utility name is too firmly rooted in historical practice of
       application programs for it to change.

       Consideration was given to mandating a diagnostic message when
       attempting to set vi-mode on terminals that do not support command
       line editing. However, it is not historical practice for the shell to
       be cognizant of all terminal types and thus be able to detect
       inappropriate terminals in all cases.  Implementations are encouraged
       to supply diagnostics in this case whenever possible, rather than
       leaving the user in a state where editing commands work incorrectly.

       In early proposals, the KornShell-derived emacs mode of command line
       editing was included, even though the emacs editor itself was not.
       The community of emacs proponents was adamant that the full emacs
       editor not be standardized because they were concerned that an
       attempt to standardize this very powerful environment would encourage
       vendors to ship strictly conforming versions lacking the
       extensibility required by the community. The author of the original
       emacs program also expressed his desire to omit the program.
       Furthermore, there were a number of historical systems that did not
       include emacs, or included it without supporting it, but there were
       very few that did not include and support vi.  The shell emacs
       command line editing mode was finally omitted because it became
       apparent that the KornShell version and the editor being distributed
       with the GNU system had diverged in some respects. The author of
       emacs requested that the POSIX emacs mode either be deleted or have a
       significant number of unspecified conditions. Although the KornShell
       author agreed to consider changes to bring the shell into alignment,
       the standard developers decided to defer specification at that time.
       At the time, it was assumed that convergence on an acceptable
       definition would occur for a subsequent draft, but that has not
       happened, and there appears to be no impetus to do so. In any case,
       implementations are free to offer additional command line editing
       modes based on the exact models of editors their users are most
       comfortable with.

       Early proposals had the following list entry in vi Line Editing
       Insert Mode:

       \     If followed by the erase or kill character, that character
             shall be inserted into the input line.  Otherwise, the
             <backslash> itself shall be inserted into the input line.

       However, this is not actually a feature of sh command line editing
       insert mode, but one of some historical terminal line drivers. Some
       conforming implementations continue to do this when the stty iexten
       flag is set.

       In interactive shells, SIGTERM is ignored so that kill 0 does not
       kill the shell, and SIGINT is caught so that wait is interruptible.
       If the shell does not ignore SIGTTIN, SIGTTOU, and SIGTSTP signals
       when it is interactive and the −m option is not in effect, these
       signals suspend the shell if it is not a session leader. If it is a
       session leader, the signals are discarded if they would stop the
       process, as required by the System Interfaces volume of POSIX.1‐2008,
       Section 2.4.3, Signal Actions for orphaned process groups.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Chapter 2, Shell Command Language, cd(1p), echo(1p), exit(1p),
       fc(1p), pwd(1p), invalid, set(1p), stty(1p), test(1p), trap(1p),
       umask(1p), vi(1p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2008, dup(3p), exec(1p),
       exit(3p), fork(3p), open(3p), pipe(3p), signal(3p), system(3p),
       ulimit(3p), umask(3p), wait(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                              SH(1P)

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