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NAME
sh — shell, the standard command language interpreter
SYNOPSIS
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
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
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
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
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
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
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
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 and Section 2.11, Signals and Error Handling).
STDOUT
See the STDERR section.
STDERR
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
None.
EXTENDED DESCRIPTION
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)
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) 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).
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).
<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.
= 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
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
See Section 2.8.1, Consequences of Shell Errors.
The following sections are informative.
APPLICATION USAGE
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
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
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
None.
SEE ALSO
Chapter 2, Shell Command Language, cd, echo, exit, fc, pwd, invalid, set, stty, test, trap, umask, vi
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(), exec, exit(), fork(), open(), pipe(), signal(),
system(), ulimit(), umask(), wait()
COPYRIGHT
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(1POSIX)