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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
SH(1P) POSIX Programmer's Manual SH(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
sh — shell, the standard command language interpreter
sh [−abCefhimnuvx] [−o option]... [+abCefhimnuvx] [+o option]...
[command_file [argument...]]
sh −c [−abCefhimnuvx] [−o option]... [+abCefhimnuvx] [+o option]...
command_string [command_name [argument...]]
sh −s [−abCefhimnuvx] [−o option]... [+abCefhimnuvx] [+o option]...
[argument...]
The sh utility is a command language interpreter that shall execute
commands read from a command line string, the standard input, or a
specified file. The application shall ensure that the commands to be
executed are expressed in the language described in Chapter 2, Shell
Command Language.
Pathname expansion shall not fail due to the size of a file.
Shell input and output redirections have an implementation-defined
offset maximum that is established in the open file description.
The sh utility shall conform to the Base Definitions volume of
POSIX.1‐2008, 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.
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.
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 is empty or consists solely of blank
lines or comments, or both, 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.
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.
The sh utility shall take the standard action for all signals (see
Section 1.4, Utility Description Defaults) with the following
exceptions.
If the shell is interactive, SIGINT signals received during command
line editing shall be handled as described in the EXTENDED
DESCRIPTION, and SIGINT signals received at other times shall be
caught but no action performed.
If the shell is interactive:
* SIGQUIT and SIGTERM signals shall be ignored.
* If the −m option is in effect, SIGTTIN, SIGTTOU, and SIGTSTP
signals shall be ignored.
* If the −m option is not in effect, it is unspecified whether
SIGTTIN, SIGTTOU, and SIGTSTP signals are ignored, set to the
default action, or caught. If they are caught, the shell shall,
in the signal-catching function, set the signal to the default
action and raise the signal (after taking any appropriate steps,
such as restoring terminal settings).
The standard actions, and the actions described above for interactive
shells, can be overridden by use of the trap special built-in utility
(see trap(1p) and Section 2.11, Signals and Error Handling).
See the STDERR section.
Except as otherwise stated (by the descriptions of any invoked
utilities or in interactive mode), standard error shall be used only
for diagnostic messages.
None.
See Chapter 2, Shell Command Language. The functionality described
in the rest of the EXTENDED DESCRIPTION section shall be provided on
implementations that support the User Portability Utilities option
(and the rest of this section is not further shaded for this option).
Command History List
When the sh utility is being used interactively, it shall maintain a
list of commands previously entered from the terminal in the file
named by the HISTFILE environment variable. The type, size, and
internal format of this file are unspecified. Multiple sh processes
can share access to the file for a user, if file access permissions
allow this; see the description of the HISTFILE environment variable.
Command Line Editing
When sh is being used interactively from a terminal, the current
command and the command history (see fc(1p)) can be edited using vi-
mode command line editing. This mode uses commands, described below,
similar to a subset of those described in the vi utility.
Implementations may offer other command line editing modes
corresponding to other editing utilities.
The command set −o vi shall enable vi-mode editing and place sh into
vi insert mode (see Command Line Editing (vi-mode)). This command
also shall disable any other editing mode that the implementation may
provide. The command set +o vi disables vi-mode editing.
Certain block-mode terminals may be unable to support shell command
line editing. If a terminal is unable to provide either edit mode, it
need not be possible to set −o vi when using the shell on this
terminal.
In the following sections, the characters erase, interrupt, kill, and
end-of-file are those set by the stty utility.
Command Line Editing (vi-mode)
In vi editing mode, there shall be a distinguished line, the edit
line. All the editing operations which modify a line affect the edit
line. The edit line is always the newest line in the command history
buffer.
With vi-mode enabled, sh can be switched between insert mode and
command mode.
When in insert mode, an entered character shall be inserted into the
command line, except as noted in vi Line Editing Insert Mode. Upon
entering sh and after termination of the previous command, sh shall
be in insert mode.
Typing an escape character shall switch sh into command mode (see vi
Line Editing Command Mode). In command mode, an entered character
shall either invoke a defined operation, be used as part of a multi-
character operation, or be treated as an error. A character that is
not recognized as part of an editing command shall terminate any
specific editing command and shall alert the terminal. If sh receives
a SIGINT signal in command mode (whether generated by typing the
interrupt character or by other means), it shall terminate command
line editing on the current command line, reissue the prompt on the
next line of the terminal, and reset the command history (see fc(1p))
so that the most recently executed command is the previous command
(that is, the command that was being edited when it was interrupted
is not re-entered into the history).
In the following sections, the phrase ``move the cursor to the
beginning of the word'' shall mean ``move the cursor to the first
character of the current word'' and the phrase ``move the cursor to
the end of the word'' shall mean ``move the cursor to the last
character of the current word''. The phrase ``beginning of the
command line'' indicates the point between the end of the prompt
string issued by the shell (or the beginning of the terminal line, if
there is no prompt string) and the first character of the command
text.
vi Line Editing Insert Mode
While in insert mode, any character typed shall be inserted in the
current command line, unless it is from the following set.
<newline> Execute the current command line. If the current command
line is not empty, this line shall be entered into the
command history (see fc(1p)).
erase Delete the character previous to the current cursor
position and move the current cursor position back one
character. In insert mode, characters shall be erased from
both the screen and the buffer when backspacing.
interrupt If sh receives a SIGINT signal in insert mode (whether
generated by typing the interrupt character or by other
means), it shall terminate command line editing with the
same effects as described for interrupting command mode;
see Command Line Editing (vi-mode).
kill Clear all the characters from the input line.
<control>‐V
Insert the next character input, even if the character is
otherwise a special insert mode character.
<control>‐W
Delete the characters from the one preceding the cursor to
the preceding word boundary. The word boundary in this case
is the closer to the cursor of either the beginning of the
line or a character that is in neither the blank nor punct
character classification of the current locale.
end-of-file
Interpreted as the end of input in sh. This interpretation
shall occur only at the beginning of an input line. If end-
of-file is entered other than at the beginning of the line,
the results are unspecified.
<ESC> Place sh into command mode.
vi Line Editing Command Mode
In command mode for the command line editing feature, decimal digits
not beginning with 0 that precede a command letter shall be
remembered. Some commands use these decimal digits as a count number
that affects the operation.
The term motion command represents one of the commands:
<space> 0 b F l W ^ $ ; E f T w | , B e h t
If the current line is not the edit line, any command that modifies
the current line shall cause the content of the current line to
replace the content of the edit line, and the current line shall
become the edit line. This replacement cannot be undone (see the u
and U commands below). The modification requested shall then be
performed to the edit line. When the current line is the edit line,
the modification shall be done directly to the edit line.
Any command that is preceded by count shall take a count (the numeric
value of any preceding decimal digits). Unless otherwise noted, this
count shall cause the specified operation to repeat by the number of
times specified by the count. Also unless otherwise noted, a count
that is out of range is considered an error condition and shall alert
the terminal, but neither the cursor position, nor the command line,
shall change.
The terms word and bigword are used as defined in the vi description.
The term save buffer corresponds to the term unnamed buffer in vi.
The following commands shall be recognized in command mode:
<newline> Execute the current command line. If the current command
line is not empty, this line shall be entered into the
command history (see fc(1p)).
<control>‐L
Redraw the current command line. Position the cursor at the
same location on the redrawn line.
# Insert the character '#' at the beginning of the current
command line and treat the resulting edit line as a
comment. This line shall be entered into the command
history; see fc(1p).
= Display the possible shell word expansions (see Section
2.6, Word Expansions) of the bigword at the current command
line position.
Note: This does not modify the content of the current
line, and therefore does not cause the current
line to become the edit line.
These expansions shall be displayed on subsequent terminal
lines. If the bigword contains none of the characters '?',
'*', or '[', an <asterisk> ('*') shall be implicitly
assumed at the end. If any directories are matched, these
expansions shall have a '/' character appended. After the
expansion, the line shall be redrawn, the cursor
repositioned at the current cursor position, and sh shall
be placed in command mode.
\ Perform pathname expansion (see Section 2.6.6, Pathname
Expansion) on the current bigword, up to the largest set of
characters that can be matched uniquely. If the bigword
contains none of the characters '?', '*', or '[', an
<asterisk> ('*') shall be implicitly assumed at the end.
This maximal expansion then shall replace the original
bigword in the command line, and the cursor shall be placed
after this expansion. If the resulting bigword completely
and uniquely matches a directory, a '/' character shall be
inserted directly after the bigword. If some other file is
completely matched, a single <space> shall be inserted
after the bigword. After this operation, sh shall be placed
in insert mode.
* Perform pathname expansion on the current bigword and
insert all expansions into the command to replace the
current bigword, with each expansion separated by a single
<space>. If at the end of the line, the current cursor
position shall be moved to the first column position
following the expansions and sh shall be placed in insert
mode. Otherwise, the current cursor position shall be the
last column position of the first character after the
expansions and sh shall be placed in insert mode. If the
current bigword contains none of the characters '?', '*',
or '[', before the operation, an <asterisk> ('*') shall be
implicitly assumed at the end.
@letter Insert the value of the alias named _letter. The symbol
letter represents a single alphabetic character from the
portable character set; implementations may support
additional characters as an extension. If the alias _letter
contains other editing commands, these commands shall be
performed as part of the insertion. If no alias _letter is
enabled, this command shall have no effect.
[count]~ Convert, if the current character is a lowercase letter, to
the equivalent uppercase letter and vice versa, as
prescribed by the current locale. The current cursor
position then shall be advanced by one character. If the
cursor was positioned on the last character of the line,
the case conversion shall occur, but the cursor shall not
advance. If the '~' command is preceded by a count, that
number of characters shall be converted, and the cursor
shall be advanced to the character position after the last
character converted. If the count is larger than the
number of characters after the cursor, this shall not be
considered an error; the cursor shall advance to the last
character on the line.
[count]. Repeat the most recent non-motion command, even if it was
executed on an earlier command line. If the previous
command was preceded by a count, and no count is given on
the '.' command, the count from the previous command shall
be included as part of the repeated command. If the '.'
command is preceded by a count, this shall override any
count argument to the previous command. The count specified
in the '.' command shall become the count for subsequent
'.' commands issued without a count.
[number]v Invoke the vi editor to edit the current command line in a
temporary file. When the editor exits, the commands in the
temporary file shall be executed and placed in the command
history. If a number is included, it specifies the command
number in the command history to be edited, rather than the
current command line.
[count]l (ell)
[count]<space>
Move the current cursor position to the next character
position. If the cursor was positioned on the last
character of the line, the terminal shall be alerted and
the cursor shall not be advanced. If the count is larger
than the number of characters after the cursor, this shall
not be considered an error; the cursor shall advance to the
last character on the line.
[count]h Move the current cursor position to the countth (default 1)
previous character position. If the cursor was positioned
on the first character of the line, the terminal shall be
alerted and the cursor shall not be moved. If the count is
larger than the number of characters before the cursor,
this shall not be considered an error; the cursor shall
move to the first character on the line.
[count]w Move to the start of the next word. If the cursor was
positioned on the last character of the line, the terminal
shall be alerted and the cursor shall not be advanced. If
the count is larger than the number of words after the
cursor, this shall not be considered an error; the cursor
shall advance to the last character on the line.
[count]W Move to the start of the next bigword. If the cursor was
positioned on the last character of the line, the terminal
shall be alerted and the cursor shall not be advanced. If
the count is larger than the number of bigwords after the
cursor, this shall not be considered an error; the cursor
shall advance to the last character on the line.
[count]e Move to the end of the current word. If at the end of a
word, move to the end of the next word. If the cursor was
positioned on the last character of the line, the terminal
shall be alerted and the cursor shall not be advanced. If
the count is larger than the number of words after the
cursor, this shall not be considered an error; the cursor
shall advance to the last character on the line.
[count]E Move to the end of the current bigword. If at the end of a
bigword, move to the end of the next bigword. If the cursor
was positioned on the last character of the line, the
terminal shall be alerted and the cursor shall not be
advanced. If the count is larger than the number of
bigwords after the cursor, this shall not be considered an
error; the cursor shall advance to the last character on
the line.
[count]b Move to the beginning of the current word. If at the
beginning of a word, move to the beginning of the previous
word. If the cursor was positioned on the first character
of the line, the terminal shall be alerted and the cursor
shall not be moved. If the count is larger than the number
of words preceding the cursor, this shall not be considered
an error; the cursor shall return to the first character on
the line.
[count]B Move to the beginning of the current bigword. If at the
beginning of a bigword, move to the beginning of the
previous bigword. If the cursor was positioned on the first
character of the line, the terminal shall be alerted and
the cursor shall not be moved. If the count is larger than
the number of bigwords preceding the cursor, this shall not
be considered an error; the cursor shall return to the
first character on the line.
^ Move the current cursor position to the first character on
the input line that is not a <blank>.
$ Move to the last character position on the current command
line.
0 (Zero.) Move to the first character position on the current
command line.
[count]| Move to the countth character position on the current
command line. If no number is specified, move to the first
position. The first character position shall be numbered 1.
If the count is larger than the number of characters on the
line, this shall not be considered an error; the cursor
shall be placed on the last character on the line.
[count]fc Move to the first occurrence of the character 'c' that
occurs after the current cursor position. If the cursor was
positioned on the last character of the line, the terminal
shall be alerted and the cursor shall not be advanced. If
the character 'c' does not occur in the line after the
current cursor position, the terminal shall be alerted and
the cursor shall not be moved.
[count]Fc Move to the first occurrence of the character 'c' that
occurs before the current cursor position. If the cursor
was positioned on the first character of the line, the
terminal shall be alerted and the cursor shall not be
moved. If the character 'c' does not occur in the line
before the current cursor position, the terminal shall be
alerted and the cursor shall not be moved.
[count]tc Move to the character before the first occurrence of the
character 'c' that occurs after the current cursor
position. If the cursor was positioned on the last
character of the line, the terminal shall be alerted and
the cursor shall not be advanced. If the character 'c' does
not occur in the line after the current cursor position,
the terminal shall be alerted and the cursor shall not be
moved.
[count]Tc Move to the character after the first occurrence of the
character 'c' that occurs before the current cursor
position. If the cursor was positioned on the first
character of the line, the terminal shall be alerted and
the cursor shall not be moved. If the character 'c' does
not occur in the line before the current cursor position,
the terminal shall be alerted and the cursor shall not be
moved.
[count]; Repeat the most recent f, F, t, or T command. Any number
argument on that previous command shall be ignored. Errors
are those described for the repeated command.
[count], Repeat the most recent f, F, t, or T command. Any number
argument on that previous command shall be ignored.
However, reverse the direction of that command.
a Enter insert mode after the current cursor position.
Characters that are entered shall be inserted before the
next character.
A Enter insert mode after the end of the current command
line.
i Enter insert mode at the current cursor position.
Characters that are entered shall be inserted before the
current character.
I Enter insert mode at the beginning of the current command
line.
R Enter insert mode, replacing characters from the command
line beginning at the current cursor position.
[count]cmotion
Delete the characters between the current cursor position
and the cursor position that would result from the
specified motion command. Then enter insert mode before the
first character following any deleted characters. If count
is specified, it shall be applied to the motion command. A
count shall be ignored for the following motion commands:
0 ^ $ c
If the motion command is the character 'c', the current
command line shall be cleared and insert mode shall be
entered. If the motion command would move the current
cursor position toward the beginning of the command line,
the character under the current cursor position shall not
be deleted. If the motion command would move the current
cursor position toward the end of the command line, the
character under the current cursor position shall be
deleted. If the count is larger than the number of
characters between the current cursor position and the end
of the command line toward which the motion command would
move the cursor, this shall not be considered an error; all
of the remaining characters in the aforementioned range
shall be deleted and insert mode shall be entered. If the
motion command is invalid, the terminal shall be alerted,
the cursor shall not be moved, and no text shall be
deleted.
C Delete from the current character to the end of the line
and enter insert mode at the new end-of-line.
S Clear the entire edit line and enter insert mode.
[count]rc Replace the current character with the character 'c'. With
a number count, replace the current and the following
count−1 characters. After this command, the current cursor
position shall be on the last character that was changed.
If the count is larger than the number of characters after
the cursor, this shall not be considered an error; all of
the remaining characters shall be changed.
[count]_ Append a <space> after the current character position and
then append the last bigword in the previous input line
after the <space>. Then enter insert mode after the last
character just appended. With a number count, append the
countth bigword in the previous line.
[count]x Delete the character at the current cursor position and
place the deleted characters in the save buffer. If the
cursor was positioned on the last character of the line,
the character shall be deleted and the cursor position
shall be moved to the previous character (the new last
character). If the count is larger than the number of
characters after the cursor, this shall not be considered
an error; all the characters from the cursor to the end of
the line shall be deleted.
[count]X Delete the character before the current cursor position and
place the deleted characters in the save buffer. The
character under the current cursor position shall not
change. If the cursor was positioned on the first character
of the line, the terminal shall be alerted, and the X
command shall have no effect. If the line contained a
single character, the X command shall have no effect. If
the line contained no characters, the terminal shall be
alerted and the cursor shall not be moved. If the count is
larger than the number of characters before the cursor,
this shall not be considered an error; all the characters
from before the cursor to the beginning of the line shall
be deleted.
[count]dmotion
Delete the characters between the current cursor position
and the character position that would result from the
motion command. A number count repeats the motion command
count times. If the motion command would move toward the
beginning of the command line, the character under the
current cursor position shall not be deleted. If the motion
command is d, the entire current command line shall be
cleared. If the count is larger than the number of
characters between the current cursor position and the end
of the command line toward which the motion command would
move the cursor, this shall not be considered an error; all
of the remaining characters in the aforementioned range
shall be deleted. The deleted characters shall be placed in
the save buffer.
D Delete all characters from the current cursor position to
the end of the line. The deleted characters shall be placed
in the save buffer.
[count]ymotion
Yank (that is, copy) the characters from the current cursor
position to the position resulting from the motion command
into the save buffer. A number count shall be applied to
the motion command. If the motion command would move toward
the beginning of the command line, the character under the
current cursor position shall not be included in the set of
yanked characters. If the motion command is y, the entire
current command line shall be yanked into the save buffer.
The current cursor position shall be unchanged. If the
count is larger than the number of characters between the
current cursor position and the end of the command line
toward which the motion command would move the cursor, this
shall not be considered an error; all of the remaining
characters in the aforementioned range shall be yanked.
Y Yank the characters from the current cursor position to the
end of the line into the save buffer. The current character
position shall be unchanged.
[count]p Put a copy of the current contents of the save buffer after
the current cursor position. The current cursor position
shall be advanced to the last character put from the save
buffer. A count shall indicate how many copies of the save
buffer shall be put.
[count]P Put a copy of the current contents of the save buffer
before the current cursor position. The current cursor
position shall be moved to the last character put from the
save buffer. A count shall indicate how many copies of the
save buffer shall be put.
u Undo the last command that changed the edit line. This
operation shall not undo the copy of any command line to
the edit line.
U Undo all changes made to the edit line. This operation
shall not undo the copy of any command line to the edit
line.
[count]k
[count]− Set the current command line to be the countth previous
command line in the shell command history. If count is not
specified, it shall default to 1. The cursor shall be
positioned on the first character of the new command. If a
k or − command would retreat past the maximum number of
commands in effect for this shell (affected by the HISTSIZE
environment variable), the terminal shall be alerted, and
the command shall have no effect.
[count]j
[count]+ Set the current command line to be the countth next command
line in the shell command history. If count is not
specified, it shall default to 1. The cursor shall be
positioned on the first character of the new command. If a
j or + command advances past the edit line, the current
command line shall be restored to the edit line and the
terminal shall be alerted.
[number]G Set the current command line to be the oldest command line
stored in the shell command history. With a number number,
set the current command line to be the command line number
in the history. If command line number does not exist, the
terminal shall be alerted and the command line shall not be
changed.
/pattern<newline>
Move backwards through the command history, searching for
the specified pattern, beginning with the previous command
line. Patterns use the pattern matching notation described
in Section 2.13, Pattern Matching Notation, except that the
'^' character shall have special meaning when it appears as
the first character of pattern. In this case, the '^' is
discarded and the characters after the '^' shall be matched
only at the beginning of a line. Commands in the command
history shall be treated as strings, not as filenames. If
the pattern is not found, the current command line shall be
unchanged and the terminal 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.
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).
See Section 2.8.1, Consequences of Shell Errors.
The following sections are informative.
Standard input and standard error are the files that determine
whether a shell is interactive when −i is not specified. For example:
sh > file
and:
sh 2> file
create interactive and non-interactive shells, respectively. Although
both accept terminal input, the results of error conditions are
different, as described in Section 2.8.1, Consequences of Shell
Errors; in the second example a redirection error encountered by a
special built-in utility aborts the shell.
A conforming application must protect its first operand, if it starts
with a <plus-sign>, by preceding it with the "−−" argument that
denotes the end of the options.
Applications should note that the standard PATH to the shell cannot
be assumed to be either /bin/sh or /usr/bin/sh, and should be
determined by interrogation of the PATH returned by getconf PATH,
ensuring that the returned pathname is an absolute pathname and not a
shell built-in.
For example, to determine the location of the standard sh utility:
command −v sh
On some implementations this might return:
/usr/xpg4/bin/sh
Furthermore, on systems that support executable scripts (the "#!"
construct), it is recommended that applications using executable
scripts install them using getconf PATH to determine the shell
pathname and update the "#!" script appropriately as it is being
installed (for example, with sed). For example:
#
# Installation time script to install correct POSIX shell pathname
#
# Get list of paths to check
#
Sifs=$IFS
Sifs_set=${IFS+y}
IFS=:
set −− $(getconf PATH)
if [ "$Sifs_set" = y ]
then
IFS=$Sifs
else
unset IFS
fi
#
# Check each path for 'sh'
#
for i
do
if [ −x "${i}"/sh ]
then
Pshell=${i}/sh
fi
done
#
# This is the list of scripts to update. They should be of the
# form '${name}.source' and will be transformed to '${name}'.
# Each script should begin:
#
# #!INSTALLSHELLPATH
#
scripts="a b c"
#
# Transform each script
#
for i in ${scripts}
do
sed −e "s|INSTALLSHELLPATH|${Pshell}|" < ${i}.source > ${i}
done
1. Execute a shell command from a string:
sh −c "cat myfile"
2. Execute a shell script from a file in the current directory:
sh my_shell_cmds
The sh utility and the set special built-in utility share a common
set of options.
The name IFS was originally an abbreviation of ``Input Field
Separators''; however, this name is misleading as the IFS characters
are actually used as field terminators. 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.
None.
Chapter 2, Shell Command Language, cd(1p), echo(1p), exit(1p),
fc(1p), pwd(1p), invalid, set(1p), stty(1p), test(1p), trap(1p),
umask(1p), vi(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2008, dup(3p), exec(1p),
exit(3p), fork(3p), open(3p), pipe(3p), signal(3p), system(3p),
ulimit(3p), umask(3p), wait(3p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SH(1P)
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