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SH(1P) POSIX Programmer's Manual SH(1P)
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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.
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 off-
set 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 exten-
sion 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 Parame-
ters) 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 imple-
mentation 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 exe-
cutable.
* 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 param-
eter 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 speci-
fied, 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 sys-
tem() 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 con-
sumed 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 char-
acters 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 Sec-
tion 2.6.2, Parameter Expansion) by the shell, and the
resulting value shall be used as a pathname of a file con-
taining 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 mecha-
nism 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 unspeci-
fied how updates to the history file from those shells inter-
act. 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 num-
ber of previous commands that are accessible. If this vari-
able 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 con-
tents 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 environ-
ment, 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 vari-
ables that are unset or null. (See the Base Definitions vol-
ume of POSIX.1-2008, Section 8.2, Internationalization Vari-
ables 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 pat-
tern 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 unspec-
ified 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 vari-
able 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 fol-
lowed by '%' and a string that shall be subjected to parame-
ter expansion and written to standard error when the modifi-
cation 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 Defini-
tions volume of POSIX.1-2008, Chapter 8, Environment Vari-
ables, 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 Sec-
tion 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 sig-
nals shall be ignored.
* If the -m option is not in effect, it is unspecified whether SIGT-
TIN, 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 utili-
ties 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 for-
mat 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 com-
mand and the command history (see fc) can be edited using vi-mode com-
mand 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 pro-
vide. 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 termi-
nal.
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 com-
mand 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 char-
acter 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 begin-
ning 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 cur-
rent 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 gener-
ated 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 com-
mand 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 con-
tains 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 com-
mand line, and the cursor shall be placed after this expan-
sion. 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 big-
word. 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 big-
word, 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 <aster-
isk> ('*') shall be implicitly assumed at the end.
@letter Insert the value of the alias named _letter. The symbol let-
ter represents a single alphabetic character from the porta-
ble 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 argu-
ment 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 posi-
tion. 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 posi-
tioned 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 posi-
tioned 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 termi-
nal 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 begin-
ning 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 posi-
tioned on the last character of the line, the terminal shall
be alerted and the cursor shall not be advanced. If the char-
acter '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 posi-
tioned on the first character of the line, the terminal shall
be alerted and the cursor shall not be moved. If the charac-
ter '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 char-
acter '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. Charac-
ters that are entered shall be inserted before the next char-
acter.
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 charac-
ter.
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 char-
acter following any deleted characters. If count is speci-
fied, 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 com-
mand 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 con-
sidered 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 big-
word 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 charac-
ter 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 char-
acters, the terminal shall be alerted and the cursor shall
not be moved. If the count is larger than the number of char-
acters 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 com-
mand. 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 con-
sidered 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 cur-
rent 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 buf-
fer. A count shall indicate how many copies of the save buf-
fer shall be put.
u Undo the last command that changed the edit line. This opera-
tion 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 com-
mand line in the shell command history. If count is not spec-
ified, it shall default to 1. The cursor shall be positioned
on the first character of the new command. If a k or - com-
mand 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 ter-
minal 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 Sec-
tion 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 dis-
carded 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 pat-
tern, 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. Pat-
terns use the pattern matching notation described in Section
2.13, Pattern Matching Notation, except that the '^' charac-
ter 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 pat-
tern, the terminal shall be alerted and the current command
line shall remain unchanged.
n Repeat the most recent / or ? command. If there is no previ-
ous / or ?, the terminal shall be alerted and the current
command line shall remain unchanged.
N Repeat the most recent / or ? command, reversing the direc-
tion of the search. If there is no previous / or ?, the ter-
minal 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 com-
mand_file not found, including but not limited to syntax, redi-
rection, or variable assignment errors.
127 A specified command_file could not be found by a non-interac-
tive 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 differ-
ent, 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 "#!" con-
struct), 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 Separa-
tors''; 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 consid-
erations, 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 per-
vasive. 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 effec-
tively preempt the user's settings of HISTFILE and HISTSIZE. For exam-
ple, 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 effec-
tive.
The default messages for the various MAIL-related messages are unspeci-
fied 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 program-
matic 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 attempt-
ing to set vi-mode on terminals that do not support command line edit-
ing. However, it is not historical practice for the shell to be cog-
nizant of all terminal types and thus be able to detect inappropriate
terminals in all cases. Implementations are encouraged to supply diag-
nostics 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 specifi-
cation at that time. At the time, it was assumed that convergence on an
acceptable definition would occur for a subsequent draft, but that has
not happened, and there appears to be no impetus to do so. In any case,
implementations are free to offer additional command line editing modes
based on the exact models of editors their users are most comfortable
with.
Early proposals had the following list entry in vi Line Editing Insert
Mode:
\ If followed by the erase or kill character, that character shall
be inserted into the input line. Otherwise, the <backslash>
itself shall be inserted into the input line.
However, this is not actually a feature of sh command line editing
insert mode, but one of some historical terminal line drivers. Some
conforming implementations continue to do this when the stty iexten
flag is set.
In interactive shells, SIGTERM is ignored so that kill 0 does not kill
the shell, and SIGINT is caught so that wait is interruptible. If the
shell does not ignore SIGTTIN, SIGTTOU, and SIGTSTP signals when it is
interactive and the -m option is not in effect, these signals suspend
the shell if it is not a session leader. If it is a session leader, the
signals are discarded if they would stop the process, as required by
the System Interfaces volume of POSIX.1-2008, Section 2.4.3, Signal
Actions for orphaned process groups.
FUTURE DIRECTIONS
None.
SEE ALSO
Chapter 2, Shell Command Language, cd, echo, exit, fc, pwd, invalid,
set, stty, test, trap, umask, vi
The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1-2008, dup(), exec, exit(),
fork(), open(), pipe(), signal(), system(), ulimit(), umask(), wait()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
cal 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.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SH(1P)
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