SH(1P) POSIX Programmer's Manual SH(1P)
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NAME
sh - shell, the standard command language interpreter
SYNOPSIS
sh [-abCefhimnuvx][-o option][+abCefhimnuvx][+o option]
[command_file [argument...]]
sh -c[-abCefhimnuvx][-o option][+abCefhimnuvx][+o option]command_string
[command_name [argument...]]
sh -s[-abCefhimnuvx][-o option][+abCefhimnuvx][+o option][argument]
DESCRIPTION
The sh utility is a command language interpreter that shall execute
commands read from a command line string, the standard input, or a
specified file. The application shall ensure that the commands to be
executed are expressed in the language described in Shell Command Lan-
guage .
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
IEEE Std 1003.1-2001, 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 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
IEEE Std 1003.1-2001).
The following additional options shall be supported:
-c Read commands from the command_string operand. Set the value of
special parameter 0 (see 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 implementa-
tion 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 unde-
fined.
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 con-
tains one or more slash characters, the implementation attempts
to read that file; the file need not be executable. If the path-
name 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 Command Search and
Execution .
Special parameter 0 (see Special Parameters ) shall be set to the value
of command_file. If sh is called using a synopsis form that omits com-
mand_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 com-
mands in command_string. If command_name is not specified, spe-
cial 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 pro-
gram), which is normally a pathname used to execute the sh util-
ity.
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
IEEE Std 1003.1-2001. 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 Parame-
ter Expansion ) by the shell, and the resulting value shall be
used as a pathname of a file containing shell commands to exe-
cute in the current environment. The file need not be exe-
cutable. If the expanded value of ENV is not an absolute path-
name, 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. This
volume of IEEE Std 1003.1-2001 specifies the effects of this
variable only for systems supporting the User Portability Utili-
ties option.
HISTFILE
Determine a pathname naming a command history file. If the HIST-
FILE 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 ini-
tializing 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 his-
tory 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. This volume of
IEEE Std 1003.1-2001 specifies the effects of this variable only
for systems supporting the User Portability Utilities option.
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 his-
tory 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 Tilde
Expansion . This volume of IEEE Std 1003.1-2001 specifies the
effects of this variable only for systems supporting the User
Portability Utilities option.
IFS (Input Field Separators.) A string treated as a list of charac-
ters that shall be used for field splitting and to split lines
into words with the read command. See Field Splitting . If IFS
is not set, the shell shall behave as if the value of IFS were
<space>, <tab>, and <newline>. Implementations may ignore the
value of IFS in the environment at the time sh is invoked,
treating IFS as if it were not set.
LANG Provide a default value for the internationalization variables
that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, 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 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 cre-
ated 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 com-
pletion 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. This volume of IEEE Std 1003.1-2001
specifies the effects of this variable only for systems support-
ing the User Portability Utilities option.
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. This volume of
IEEE Std 1003.1-2001 specifies the effects of this variable only
for systems supporting the User Portability Utilities option.
MAILPATH
Provide a list of pathnames and optional messages separated by
colons. 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 vari-
able. This volume of IEEE Std 1003.1-2001 specifies the effects of this
variable only for systems supporting the User Portability Utilities
option.
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 IEEE Std 1003.1-2001, Chapter 8, Environment
Variables, used to effect command interpretation; see Command
Search and Execution .
PWD This variable shall represent an absolute pathname of the cur-
rent working directory. Assignments to this variable may be
ignored unless the value is an absolute pathname of the current
working directory and there are no filename components of dot or
dot-dot.
ASYNCHRONOUS EVENTS
Default.
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 Shell Command Language . The following additional capabilities are
supported on systems supporting the User Portability Utilities 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 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. Typing the interrupt
character in command mode shall cause sh to 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 reen-
tered 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 charac-
ter 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
Terminate command line editing with the same effects as
described for interrupting command mode; see Command Line Edit-
ing (vi-mode) .
kill Clear all the characters from the input line.
<control>-V
Insert the next character input, even if the character is other-
wise 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 clas-
sification 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 Word Expansions
) of the bigword at the current command line position.
Note:
This does not modify the content of the current line, and there-
fore 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 aster-
isk ( '*' ) 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 Pathname Expansion ) on the cur-
rent bigword, up to the largest set of characters that can be
matched uniquely. If the bigword contains none of the charac-
ters '?', '*', 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 com-
pletely 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 char-
acter set; implementations may support additional characters as
an extension. If the alias _letter contains other editing com-
mands, these commands shall be performed as part of the inser-
tion. 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 exe-
cuted 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 tem-
porary file. When the editor exits, the commands in the tempo-
rary 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) pre-
vious 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 con-
sidered 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 char-
acter on the line.
[count]W
Move to the start of the next bigword. 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 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 char-
acter on the line.
[count]E
Move to the end of the current bigword. If at the end of a big-
word, 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 cur-
sor, 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 begin-
ning of a bigword, move to the beginning of the previous big-
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 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 com-
mand 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 charac-
ter '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 cur-
rent cursor position, the terminal shall be alerted and the cur-
sor shall not be moved.
[count]Tc
Move to the character after the first occurrence of the charac-
ter '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 argu-
ment 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 argu-
ment 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 fol-
lowing 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 com-
mand 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 posi-
tion toward the end of the command line, the character under the cur-
rent 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 charac-
ters 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 cur-
sor was positioned on the first character of the line, the ter-
minal 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 termi-
nal 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 com-
mand. A number count repeats the motion command count times. If
the motion command would move toward the beginning of the com-
mand 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 buf-
fer.
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 posi-
tion 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 Pattern
Matching Notation, except that the '^' character shall have spe-
cial 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 file-
names. 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. Pat-
terns use the pattern matching notation described in Pattern
Matching Notation, except that the '^' character shall have spe-
cial 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 file-
names. 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 a syntax, redirection, or vari-
able assignment error.
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 Special
Built-In Utilities ).
CONSEQUENCES OF ERRORS
See 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 Consequences of Shell Errors ; in the second exam-
ple 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 -v 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
IFS=:
set $(getconf PATH)
IFS=$Sifs
#
# Check each path for 'sh'
#
for i in $@
do
if [ -f ${i}/sh ];
then
Pshell=${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 -p
#
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 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 pre-
vents 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 IEEE Std 1003.1-2001. 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 IEEE Std 1003.1-2001 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
IEEE Std 1003.1-2001.
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 effective.
The default messages for the various MAIL -related messages are unspec-
ified 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 IEEE Std 1003.1-2001 so that interactive
users can also be application programmers without having to deal with
programmatic differences in their two environments. It is also essen-
tial that the utility name sh be specified because this explicit util-
ity 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.
FUTURE DIRECTIONS
None.
SEE ALSO
Shell Command Language, cd, echo, exit(), fc, pwd, read(), set, stty,
test, umask(), vi, the System Interfaces volume of
IEEE Std 1003.1-2001, dup(), exec, exit(), fork(), open(), pipe(), sig-
nal(), system(), ulimit(), umask(), wait()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SH(1P)
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