sh

SH(1POSIX)                  POSIX Programmer's Manual                 SH(1POSIX)



PROLOG
       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 offset
       maximum that is established in the open file description.

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

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

       The following additional options shall be supported:

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

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

       −s        Read commands from the standard input.

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

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

OPERANDS
       The following operands shall be supported:

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

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

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

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

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

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

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

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

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

        *  The −s option is specified.

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

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

       See the INPUT FILES section.

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

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

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

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of sh:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

                 The MAILPATH environment variable takes precedence over the
                 MAIL variable.

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

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

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

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

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

       If the shell is interactive:

        *  SIGQUIT and SIGTERM signals shall be ignored.

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

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

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

STDOUT
       See the STDERR section.

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

OUTPUT FILES
       None.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       kill      Clear all the characters from the input line.

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

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

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

       <ESC>     Place sh into command mode.

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

       The term motion command represents one of the commands:

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

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

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

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

       The following commands shall be recognized in command mode:

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

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

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

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

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

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

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

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

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

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

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

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

       [count]l   (ell)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

                     0    ^    $    c

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

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

       S         Clear the entire edit line and enter insert mode.

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

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

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

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

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

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

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

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

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

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

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

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

       [count]k

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

       [count]j

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

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

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

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

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

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

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

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

EXIT STATUS
       The following exit values shall be returned:

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

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

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

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

CONSEQUENCES OF ERRORS
       See Section 2.8.1, Consequences of Shell Errors.

       The following sections are informative.

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

           sh > file

       and:

           sh 2> file

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

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

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

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

           command −v sh

       On some implementations this might return:

           /usr/xpg4/bin/sh

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

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

EXAMPLES
        1. Execute a shell command from a string:

               sh −c "cat myfile"

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

               sh my_shell_cmds

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

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

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

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

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

           sh −

       or by:

           #! usr/bin/sh −

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

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

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

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

           "you have mail\n"

       or:

           "you have new mail\n"

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

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

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

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

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

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

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

FUTURE DIRECTIONS
       None.

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 Electrical
       and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008
       with the 2013 Technical Corrigendum 1 applied.) In the event of any
       discrepancy between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group Standard is the referee
       document. The original Standard can be obtained online at
       http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most
       likely to have been introduced during the conversion of the source files
       to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                   2013                            SH(1POSIX)