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 and Section 2.11, Signals
and Error Handling).
Except as otherwise stated (by the descriptions of any invoked
utilities or in interactive mode), standard error shall be used only for
diagnostic messages.
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).
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.
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.
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.
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.
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:
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:
and:
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:
On some implementations this might return:
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:
- 2.
- Execute a shell script from a file in the current directory:
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:
or by:
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:
or:
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.
Section 2.9.1.1, Command Search and Execution,
Chapter 2, Shell Command Language, cd,
echo, exit, fc, pwd,
invalid, set, stty, test,
trap, umask, vi
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(), exec, exit(),
fork(), open(), pipe(),
signal(), system(), ulimit(),
umask(), wait()
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 .