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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 |
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SH(1P) POSIX Programmer's Manual SH(1P)
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.
sh — shell, the standard command language interpreter
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...]
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.
The sh utility shall conform to the Base Definitions volume of
POSIX.1‐2017, 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-minus> (meaning the reverse
case of the option as described in this volume of POSIX.1‐2017).
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.
The following operands shall be supported:
- A single <hyphen-minus> 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-minus>, 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.1‐2017. If the command_string operand is
an empty string, sh shall exit with a zero exit status.
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.
The input file shall be a text file, except that line lengths
shall be unlimited. If the input file consists solely of zero or
more blank lines and comments, sh shall exit with a zero exit
status.
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.
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, 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.1‐2017, 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.
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).
See the STDERR section.
Except as otherwise stated (by the descriptions of any invoked
utilities or in interactive mode), standard error shall be used
only for diagnostic messages.
None.
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 shall be 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 shall be 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.
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 or executable, including but not
limited to syntax, redirection, or variable assignment
errors.
126 A specified command_file could not be executed due to an
[ENOEXEC] error (see Section 2.9.1.1, Command Search and
Execution, item 2).
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).
See Section 2.8.1, Consequences of Shell Errors.
The following sections are informative.
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
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
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. One
justification for ignoring the contents of IFS upon entry to the
script, 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.1‐2017. 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.1‐2017 allows the single <hyphen-minus>
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.1‐2017.
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.1‐2017, Section 2.4.3, Signal Actions for orphaned
process groups.
None.
Section 2.9.1.1, Command Search and Execution, 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.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, dup(3p), exec(1p),
exit(3p), fork(3p), open(3p), pipe(3p), signal(3p), system(3p),
ulimit(3p), umask(3p), wait(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. 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.opengroup.org/unix/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 2017 SH(1P)
Pages that refer to this page: command(1p), ed(1p), ex(1p), fc(1p), find(1p), make(1p), newgrp(1p), nohup(1p), script(1), time(1p), wait(1p), popen(3p), system(3p)
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