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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (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 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 IEEE Std 1003.1-2001, Section 12.2, Utility Syn-
       tax 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 Parame-
              ters  )  from the value of the command_name operand and the positional parameters ($1, $2, and so on) in
              sequence from the remaining argument operands. No commands shall be read from the standard input.

       -i     Specify that the shell is interactive; see below. An 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 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 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  exe-
       cute 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 argu-
              ment  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 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 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. This volume of
              IEEE Std 1003.1-2001 specifies the effects of this variable only for systems supporting the User  Porta-
              bility Utilities option.

       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 imple-
              mentation may choose to access this variable only when initializing the history file;  this  initializa-
              tion  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 phys-
              ically 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 accessi-
              ble. 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 implementa-
              tion 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  Tilde Expansion . This volume of IEEE Std 1003.1-2001 specifies the effects of this vari-
              able only for systems supporting the User Portability Utilities option.

       IFS    (Input Field Separators.) A string treated as a list of characters that shall be used for  field  split-
              ting  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 Variables for  the  prece-
              dence 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 exam-
              ple, 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 match-
              ing.

       LC_MESSAGES
              Determine the locale that should be used to affect the format and contents of diagnostic messages  writ-
              ten 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 unspeci-
              fied 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.  This  volume  of
              IEEE Std 1003.1-2001  specifies the effects of this variable only for systems supporting the User Porta-
              bility 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 Porta-
              bility 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 variable. 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 Definitions volume of IEEE Std 1003.1-2001, Chap-
              ter 8, Environment Variables, used to effect command interpretation; see Command Search and Execution  .

       PWD    This variable shall represent an absolute pathname of the current 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 utilities 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 per-
       missions 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 opera-
       tion, or be treated as an error. A character that is not recognized as part of an editing command shall  termi-
       nate  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 reentered into  the
       history).

       In  the following sections, the phrase "move the cursor to the beginning of the word" shall mean "move the cur-
       sor 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
              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  bound-
              ary  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 com-
       mand 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 per-
       formed 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  speci-
       fied  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 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 charac-
       ters '?', '*', 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 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  big-
              word  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 char-
              acters  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 num-
              ber 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 char-
              acter 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 posi-
              tion, 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 cur-
       rent 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 char-
              acter  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 num-
              ber 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 con-
              tained 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 charac-
              ters 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 cur-
              sor  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 com-
              mand 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 pre-
              vious command line. Patterns use the pattern matching notation described in Pattern  Matching  Notation,
              except  that the '^' character shall have special meaning when it appears as the first character of pat-
              tern. 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 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 pat-
              tern 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 variable 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 different, as described in Consequences of Shell Errors ; in the second example a redi-
       rection 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  applica-
       tions  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 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, proba-
       bly 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 immedi-
       ately 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 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 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 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  his-
       tory  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 implemen-
       tation-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 implemen-
       tations.  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 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  addi-
       tional 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. Other-
              wise, 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 ter-
       minal 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(),  signal(),  system(),  ulimit(),
       umask(), wait()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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)