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SH(1)                   FreeBSD General Commands Manual                  SH(1)

       sh, for, case, if, while, :, ., break, continue, cd, eval, exec, exit,
       export, login, newgrp, read, readonly, set, shift, times, trap, umask,
       wait - command language

       sh [ -ceiknrstuvx ] [ arg ] ...

       Sh is a command programming language that executes commands read from a
       terminal or a file.  See invocation for the meaning of arguments to the

       A simple-command is a sequence of non blank words separated by blanks
       (a blank is a tab or a space).  The first word specifies the name of
       the command to be executed.  Except as specified below the remaining
       words are passed as arguments to the invoked command.  The command name
       is passed as argument 0 (see exec(2)).  The value of a simple-command
       is its exit status if it terminates normally or 200+status if it
       terminates abnormally (see signal(2) for a list of status values).

       A pipeline is a sequence of one or more commands separated by |.  The
       standard output of each command but the last is connected by a pipe(2)
       to the standard input of the next command.  Each command is run as a
       separate process; the shell waits for the last command to terminate.

       A list is a sequence of one or more pipelines separated by ;, &, && or
       || and optionally terminated by ; or &.  ; and & have equal precedence
       which is lower than that of && and ||, && and || also have equal
       precedence.  A semicolon causes sequential execution; an ampersand
       causes the preceding pipeline to be executed without waiting for it to
       finish.  The symbol && (||) causes the list following to be executed
       only if the preceding pipeline returns a zero (non zero) value.
       Newlines may appear in a list, instead of semicolons, to delimit

       A command is either a simple-command or one of the following.  The
       value returned by a command is that of the last simple-command executed
       in the command.

       for name [in word ...] do list done
              Each time a for command is executed name is set to the next word
              in the for word list If in word ...  is omitted then in "$@" is
              assumed.  Execution ends when there are no more words in the

       case word in [pattern [ | pattern ] ... ) list ;;] ... esac
              A case command executes the list associated with the first
              pattern that matches word.  The form of the patterns is the same
              as that used for file name generation.

       if list then list [elif list then list] ... [else list] fi
              The list following if is executed and if it returns zero the
              list following then is executed.  Otherwise, the list following
              elif is executed and if its value is zero the list following
              then is executed.  Failing that the else list is executed.

       while list [do list] done
              A while command repeatedly executes the while list and if its
              value is zero executes the do list; otherwise the loop
              terminates.  The value returned by a while command is that of
              the last executed command in the do list.  until may be used in
              place of while to negate the loop termination test.

       ( list )
              Execute list in a subshell.

       { list }
              list is simply executed.

       The following words are only recognized as the first word of a command
       and when not quoted.

              if then else elif fi case in esac for while until do done { }

       Command substitution.
       The standard output from a command enclosed in a pair of grave accents
       (``) may be used as part or all of a word; trailing newlines are

       Parameter substitution.
       The character $ is used to introduce substitutable parameters.
       Positional parameters may be assigned values by set.  Variables may be
       set by writing

              name=value [ name=value ] ...

              A parameter is a sequence of letters, digits or underscores (a
              name), a digit, or any of the characters * @ # ? - $ !.  The
              value, if any, of the parameter is substituted.  The braces are
              required only when parameter is followed by a letter, digit, or
              underscore that is not to be interpreted as part of its name.
              If parameter is a digit then it is a positional parameter.  If
              parameter is * or @ then all the positional parameters, starting
              with $1, are substituted separated by spaces.  $0 is set from
              argument zero when the shell is invoked.

              If parameter is set then substitute its value; otherwise
              substitute word.

              If parameter is not set then set it to word; the value of the
              parameter is then substituted.  Positional parameters may not be
              assigned to in this way.

              If parameter is set then substitute its value; otherwise, print
              word and exit from the shell.  If word is omitted then a
              standard message is printed.

              If parameter is set then substitute word; otherwise substitute

       In the above word is not evaluated unless it is to be used as the
       substituted string.  (So that, for example, echo ${d-`pwd`} will only
       execute pwd if d is unset.)

       The following parameters are automatically set by the shell.

              #      The number of positional parameters in decimal.
              -      Options supplied to the shell on invocation or by set.
              ?      The value returned by the last executed command in
              $      The process number of this shell.
              !      The process number of the last background command

       The following parameters are used but not set by the shell.

              HOME   The default argument (home directory) for the cd command.
              PATH   The search path for commands (see execution).
              MAIL   If this variable is set to the name of a mail file then
                     the shell informs the user of the arrival of mail in the
                     specified file.
              PS1    Primary prompt string, by default `$ '.
              PS2    Secondary prompt string, by default `> '.
              IFS    Internal field separators, normally space, tab, and

       Blank interpretation.
       After parameter and command substitution, any results of substitution
       are scanned for internal field separator characters (those found in
       $IFS) and split into distinct arguments where such characters are
       found.  Explicit null arguments ("" or '') are retained.  Implicit null
       arguments (those resulting from parameters that have no values) are

       File name generation.
       Following substitution, each command word is scanned for the characters
       *, ?  and [.  If one of these characters appears then the word is
       regarded as a pattern.  The word is replaced with alphabetically sorted
       file names that match the pattern.  If no file name is found that
       matches the pattern then the word is left unchanged.  The character .
       at the start of a file name or immediately following a /, and the
       character /, must be matched explicitly.

       *      Matches any string, including the null string.
       ?      Matches any single character.
       [...]  Matches any one of the characters enclosed.  A pair of
              characters separated by - matches any character lexically
              between the pair.

       The following characters have a special meaning to the shell and cause
       termination of a word unless quoted.

            ;   &   (   )   |   <   >   newline   space   tab

       A character may be quoted by preceding it with a \.  \newline is
       ignored.  All characters enclosed between a pair of quote marks (''),
       except a single quote, are quoted.  Inside double quotes ("") parameter
       and command substitution occurs and \ quotes the characters \ ` " and

       "$*" is equivalent to "$1 $2 ..." whereas
       "$@" is equivalent to "$1" "$2" ... .

       When used interactively, the shell prompts with the value of PS1 before
       reading a command.  If at any time a newline is typed and further input
       is needed to complete a command then the secondary prompt ($PS2) is

       Input output.
       Before a command is executed its input and output may be redirected
       using a special notation interpreted by the shell.  The following may
       appear anywhere in a simple-command or may precede or follow a command
       and are not passed on to the invoked command.  Substitution occurs
       before word or digit is used.

       <word  Use file word as standard input (file descriptor 0).

       >word  Use file word as standard output (file descriptor 1).  If the
              file does not exist then it is created; otherwise it is
              truncated to zero length.

       >>word Use file word as standard output.  If the file exists then
              output is appended (by seeking to the end); otherwise the file
              is created.

       <<word The shell input is read up to a line the same as word, or end of
              file.  The resulting document becomes the standard input.  If
              any character of word is quoted then no interpretation is placed
              upon the characters of the document; otherwise, parameter and
              command substitution occurs, \newline is ignored, and \ is used
              to quote the characters \ $ ` and the first character of word.

              The standard input is duplicated from file descriptor digit; see
              dup(2).  Similarly for the standard output using >.

       <&-    The standard input is closed.  Similarly for the standard output
              using >.

       If one of the above is preceded by a digit then the file descriptor
       created is that specified by the digit (instead of the default 0 or 1).
       For example,

            ... 2>&1

       creates file descriptor 2 to be a duplicate of file descriptor 1.

       If a command is followed by & then the default standard input for the
       command is the empty file (/dev/null).  Otherwise, the environment for
       the execution of a command contains the file descriptors of the
       invoking shell as modified by input output specifications.

       The environment is a list of name-value pairs that is passed to an
       executed program in the same way as a normal argument list; see exec(2)
       and environ(5).  The shell interacts with the environment in several
       ways.  On invocation, the shell scans the environment and creates a
       parameter for each name found, giving it the corresponding value.
       Executed commands inherit the same environment.  If the user modifies
       the values of these parameters or creates new ones, none of these
       affects the environment unless the export command is used to bind the
       shell's parameter to the environment.  The environment seen by any
       executed command is thus composed of any unmodified name-value pairs
       originally inherited by the shell, plus any modifications or additions,
       all of which must be noted in export commands.

       The environment for any simple-command may be augmented by prefixing it
       with one or more assignments to parameters.  Thus these two lines are

              TERM=450 cmd args
              (export TERM; TERM=450; cmd args)

       If the -k flag is set, all keyword arguments are placed in the
       environment, even if the occur after the command name.  The following
       prints `a=b c' and `c':
       echo a=b c
       set -k
       echo a=b c

       The INTERRUPT and QUIT signals for an invoked command are ignored if
       the command is followed by &; otherwise signals have the values
       inherited by the shell from its parent.  (But see also trap.)

       Each time a command is executed the above substitutions are carried
       out.  Except for the `special commands' listed below a new process is
       created and an attempt is made to execute the command via an exec(2).

       The shell parameter $PATH defines the search path for the directory
       containing the command.  Each alternative directory name is separated
       by a colon (:).  The default path is :/bin:/usr/bin.  If the command
       name contains a / then the search path is not used.  Otherwise, each
       directory in the path is searched for an executable file.  If the file
       has execute permission but is not an a.out file, it is assumed to be a
       file containing shell commands.  A subshell (i.e., a separate process)
       is spawned to read it.  A parenthesized command is also executed in a

       Special commands.
       The following commands are executed in the shell process and except
       where specified no input output redirection is permitted for such

       :      No effect; the command does nothing.
       . file Read and execute commands from file and return.  The search path
              $PATH is used to find the directory containing file.
       break [n]
              Exit from the enclosing for or while loop, if any.  If n is
              specified then break n levels.
       continue [n]
              Resume the next iteration of the enclosing for or while loop.
              If n is specified then resume at the n-th enclosing loop.
       cd [arg]
              Change the current directory to arg.  The shell parameter $HOME
              is the default arg.
       eval [arg ...]
              The arguments are read as input to the shell and the resulting
              command(s) executed.
       exec [arg ...]
              The command specified by the arguments is executed in place of
              this shell without creating a new process.  Input output
              arguments may appear and if no other arguments are given cause
              the shell input output to be modified.
       exit [n]
              Causes a non interactive shell to exit with the exit status
              specified by n.  If n is omitted then the exit status is that of
              the last command executed.  (An end of file will also exit from
              the shell.)
       export [name ...]
              The given names are marked for automatic export to the
              environment of subsequently-executed commands.  If no arguments
              are given then a list of exportable names is printed.
       login [arg ...]
              Equivalent to `exec login arg ...'.
       newgrp [arg ...]
              Equivalent to `exec newgrp arg ...'.
       read name ...
              One line is read from the standard input; successive words of
              the input are assigned to the variables name in order, with
              leftover words to the last variable.  The return code is 0
              unless the end-of-file is encountered.
       readonly [name ...]
              The given names are marked readonly and the values of the these
              names may not be changed by subsequent assignment.  If no
              arguments are given then a list of all readonly names is
       set [-eknptuvx [arg ...]]
              -e If non interactive then exit immediately if a command fails.
              -k All keyword arguments are placed in the environment for a
                 command, not just those that precede the command name.
              -n Read commands but do not execute them.
              -t Exit after reading and executing one command.
              -u Treat unset variables as an error when substituting.
              -v Print shell input lines as they are read.
              -x Print commands and their arguments as they are executed.
              -  Turn off the -x and -v options.

              These flags can also be used upon invocation of the shell.  The
              current set of flags may be found in $-.

              Remaining arguments are positional parameters and are assigned,
              in order, to $1, $2, etc.  If no arguments are given then the
              values of all names are printed.

       shift  The positional parameters from $2...  are renamed $1...

       times  Print the accumulated user and system times for processes run
              from the shell.

       trap [arg] [n] ...
              Arg is a command to be read and executed when the shell receives
              signal(s) n.  (Note that arg is scanned once when the trap is
              set and once when the trap is taken.)  Trap commands are
              executed in order of signal number.  If arg is absent then all
              trap(s) n are reset to their original values.  If arg is the
              null string then this signal is ignored by the shell and by
              invoked commands.  If n is 0 then the command arg is executed on
              exit from the shell, otherwise upon receipt of signal n as
              numbered in signal(2).  Trap with no arguments prints a list of
              commands associated with each signal number.

       umask [ nnn ]
              The user file creation mask is set to the octal value nnn (see
              umask(2)).  If nnn is omitted, the current value of the mask is

       wait [n]
              Wait for the specified process and report its termination
              status.  If n is not given then all currently active child
              processes are waited for.  The return code from this command is
              that of the process waited for.

       If the first character of argument zero is -, commands are read from
       $HOME/.profile, if such a file exists.  Commands are then read as
       described below.  The following flags are interpreted by the shell when
       it is invoked.
       -c string  If the -c flag is present then commands are read from
       -s         If the -s flag is present or if no arguments remain then
                  commands are read from the standard input.  Shell output is
                  written to file descriptor 2.
       -i         If the -i flag is present or if the shell input and output
                  are attached to a terminal (as told by gtty) then this shell
                  is interactive.  In this case the terminate signal SIGTERM
                  (see signal(2)) is ignored (so that `kill 0' does not kill
                  an interactive shell) and the interrupt signal SIGINT is
                  caught and ignored (so that wait is interruptable).  In all
                  cases SIGQUIT is ignored by the shell.

       The remaining flags and arguments are described under the set command.


       test(1), exec(2),

       Errors detected by the shell, such as syntax errors cause the shell to
       return a non zero exit status.  If the shell is being used non
       interactively then execution of the shell file is abandoned.
       Otherwise, the shell returns the exit status of the last command
       executed (see also exit).

       If << is used to provide standard input to an asynchronous process
       invoked by &, the shell gets mixed up about naming the input document.
       A garbage file /tmp/sh* is created, and the shell complains about not
       being able to find the file by another name.



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