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PROGRAM:

NAME

sh — shell, the standard command language interpreter

SYNOPSIS

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

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

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

DESCRIPTION

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

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

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

OPTIONS

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

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

The following additional options shall be supported:

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

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

−s Read commands from the standard input.

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

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

OPERANDS

The following operands shall be supported:

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

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

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

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

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

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

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

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

STDIN

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

* The −s option is specified.

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

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

See the INPUT FILES section.

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

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

INPUT FILES

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

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of sh:

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

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

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

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

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

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

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

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

LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2,
Internationalization Variables for the precedence of internationalization
variables used to determine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.

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

LC_CTYPE Determine the locale for the interpretation of sequences of bytes of text data
as characters (for example, single-byte as opposed to multi-byte characters in
arguments and input files), which characters are defined as letters (character
class alpha), and the behavior of character classes within pattern matching.

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

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

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

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

The MAILPATH environment variable takes precedence over the MAIL variable.

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

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

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

ASYNCHRONOUS EVENTS

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

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

If the shell is interactive:

* SIGQUIT and SIGTERM signals shall be ignored.

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

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

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

STDOUT

See the STDERR section.

STDERR

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

OUTPUT FILES

None.

EXTENDED DESCRIPTION

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

kill Clear all the characters from the input line.

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

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

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

<ESC> Place sh into command mode.

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

The term motion command represents one of the commands:

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

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

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

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

The following commands shall be recognized in command mode:

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

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

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

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

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

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

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

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

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

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

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

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

[count]l (ell)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

0 ^ $ c

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

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

S Clear the entire edit line and enter insert mode.

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

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

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

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

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

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

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

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

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

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

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

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

[count]k

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

[count]j

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

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

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

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

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

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

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

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

EXIT STATUS

The following exit values shall be returned:

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

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

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

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

CONSEQUENCES OF ERRORS

See Section 2.8.1, Consequences of Shell Errors.

The following sections are informative.

APPLICATION USAGE

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

sh > file

and:

sh 2> file

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

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

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

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

command −v sh

On some implementations this might return:

/usr/xpg4/bin/sh

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

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

EXAMPLES

1. Execute a shell command from a string:

sh −c "cat myfile"

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

sh my_shell_cmds

RATIONALE

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

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

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

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

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

sh −

or by:

#! usr/bin/sh −

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

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

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

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

"you have mail\n"

or:

"you have new mail\n"

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

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

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

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

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

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

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

FUTURE DIRECTIONS

None.

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