32v 1m sh

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SH(1) UNIX Programmer's 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 ] ...


    _S_h is a command programming language that executes commands
    read from a terminal or a file.  See invocation for the
    meaning of arguments to the shell.
    A _s_i_m_p_l_e-_c_o_m_m_a_n_d is a sequence of non blank _w_o_r_d_s 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 argu-
    ment 0 (see _e_x_e_c(2)).  The _v_a_l_u_e of a simple-command is its
    exit status if it terminates normally or 200+_s_t_a_t_u_s if it
    terminates abnormally (see _s_i_g_n_a_l(2) for a list of status
    A _p_i_p_e_l_i_n_e is a sequence of one or more _c_o_m_m_a_n_d_s separated
    by |. The standard output of each command but the last is
    connected by a _p_i_p_e(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 _l_i_s_t is a sequence of one or more _p_i_p_e_l_i_n_e_s 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
    _p_i_p_e_l_i_n_e to be executed without waiting for it to finish.
    The symbol && (||) causes the _l_i_s_t following to be executed
    only if the preceding _p_i_p_e_l_i_n_e returns a zero (non zero)
    value.  Newlines may appear in a _l_i_s_t, instead of semi-
    colons, to delimit commands.
    A _c_o_m_m_a_n_d is either a simple-command or one of the follow-
    ing.  The value returned by a command is that of the last
    simple-command executed in the command.
    for _n_a_m_e [in _w_o_r_d ...] do _l_i_s_t done
         Each time a for command is executed _n_a_m_e is set to the
         next word in the for word list If in _w_o_r_d ...  is omit-
         ted then in "$@" is assumed.  Execution ends when there
         are no more words in the list.
    case _w_o_r_d in [_p_a_t_t_e_r_n [ | _p_a_t_t_e_r_n ] ... ) _l_i_s_t ;;] ... esac
         A case command executes the _l_i_s_t associated with the
         first pattern that matches _w_o_r_d. The form of the pat-
         terns is the same as that used for file name genera-
    if _l_i_s_t then _l_i_s_t [elif _l_i_s_t then _l_i_s_t] ... [else _l_i_s_t] fi
         The _l_i_s_t following if is executed and if it returns
         zero the _l_i_s_t following then is executed.  Otherwise,
         the _l_i_s_t following elif is executed and if its value is
         zero the _l_i_s_t following then is executed.  Failing that
         the else _l_i_s_t is executed.
    while _l_i_s_t [do _l_i_s_t] done
         A while command repeatedly executes the while _l_i_s_t and
         if its value is zero executes the do _l_i_s_t; otherwise
         the loop terminates.  The value returned by a while
         command is that of the last executed command in the do
         _l_i_s_t. until may be used in place of while to negate the
         loop termination test.
    ( _l_i_s_t )
         Execute _l_i_s_t in a subshell.
    { _l_i_s_t }
         _l_i_s_t 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 removed.
    Parameter substitution.
    The character $ is used to introduce substitutable parame-
    ters.  Positional parameters may be assigned values by set.
    Variables may be set by writing
         _n_a_m_e=_v_a_l_u_e [ _n_a_m_e=_v_a_l_u_e ] ...
         A _p_a_r_a_m_e_t_e_r is a sequence of letters, digits or under-
         scores (a _n_a_m_e), a digit, or any of the characters * @
         # ? - $ !.  The value, if any, of the parameter is sub-
         stituted.  The braces are required only when _p_a_r_a_m_e_t_e_r
         is followed by a letter, digit, or underscore that is
         not to be interpreted as part of its name.  If _p_a_r_a_m_e_-
         _t_e_r is a digit then it is a positional parameter.  If
         _p_a_r_a_m_e_t_e_r 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 _p_a_r_a_m_e_t_e_r is set then substitute its value; other-
         wise substitute _w_o_r_d.
         If _p_a_r_a_m_e_t_e_r is not set then set it to _w_o_r_d; the value
         of the parameter is then substituted.  Positional
         parameters may not be assigned to in this way.
         If _p_a_r_a_m_e_t_e_r is set then substitute its value; other-
         wise, print _w_o_r_d and exit from the shell.  If _w_o_r_d is
         omitted then a standard message is printed.
         If _p_a_r_a_m_e_t_e_r is set then substitute _w_o_r_d; otherwise
         substitute nothing.
    In the above _w_o_r_d is not evaluated unless it is to be used
    as the substituted string.  (So that, for example, echo
    ${d-`pwd`} will only execute _p_w_d if _d is unset.)
    The following _p_a_r_a_m_e_t_e_r_s are automatically set by the shell.
         #    The number of positional parameters in decimal.
         -    Options supplied to the shell on invocation or by
         ?    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 _p_a_r_a_m_e_t_e_r_s are used but not set by the shell.
         HOME The default argument (home directory) for the cd
         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 newline.
    Blank interpretation.
    After parameter and command substitution, any results of
    substitution are scanned for internal field separator char-
    acters (those found in $IFS) and split into distinct argu-
    ments where such characters are found.  Explicit null argu-
    ments ("" or ) are retained.  Implicit null arguments
    (those resulting from _p_a_r_a_m_e_t_e_r_s 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 pat-
    tern 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 lexi-
         cally 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 _q_u_o_t_e_d by preceding it with a \.  \new-
    line 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 issued.
    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 _c_o_m_m_a_n_d and are not
    passed on to the invoked command.  Substitution occurs
    before _w_o_r_d or _d_i_g_i_t is used.
         Use file _w_o_r_d as standard input (file descriptor 0).
         Use file _w_o_r_d as standard output (file descriptor 1).
         If the file does not exist then it is created; other-
         wise it is truncated to zero length.
         Use file _w_o_r_d as standard output.  If the file exists
         then output is appended (by seeking to the end); other-
         wise the file is created.
         The shell input is read up to a line the same as _w_o_r_d,
         or end of file.  The resulting document becomes the
         standard input.  If any character of _w_o_r_d is quoted
         then no interpretation is placed upon the characters of
         the document; otherwise, parameter and command substi-
         tution occurs, \newline is ignored, and \ is used to
         quote the characters \ $ ` and the first character of
         The standard input is duplicated from file descriptor
         _d_i_g_i_t; see _d_u_p(2).  Similarly for the standard output
         using >.
    <&-  The standard input is closed.  Similarly for the stan-
         dard 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 descrip-
    tor 1.
    If a command is followed by & then the default standard
    input for the command is the empty file (/dev/null).  Other-
    wise, the environment for the execution of a command con-
    tains 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 _e_x_e_c(2) and _e_n_v_i_r_o_n(5).  The shell interacts with
    the environment in several ways.  On invocation, the shell
    scans the environment and creates a _p_a_r_a_m_e_t_e_r for each name
    found, giving it the corresponding value.  Executed commands
    inherit the same environment.  If the user modifies the
    values of these _p_a_r_a_m_e_t_e_r_s or creates new ones, none of
    these affects the environment unless the export command is
    used to bind the shell's _p_a_r_a_m_e_t_e_r 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 _s_i_m_p_l_e-_c_o_m_m_a_n_d may be augmented by
    prefixing it with one or more assignments to _p_a_r_a_m_e_t_e_r_s.
    Thus these two lines are equivalent
         TERM=450 cmd args
         (export TERM; TERM=450; cmd args)
    If the -k flag is set, _a_l_l 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 _e_x_e_c(2).
    The shell parameter $PATH defines the search path for the
    directory containing the command.  Each alternative direc-
    tory 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._o_u_t 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 subshell.
    Special commands.
    The following commands are executed in the shell process and
    except where specified no input output redirection is per-
    mitted for such commands.
    :    No effect; the command does nothing.
    . _f_i_l_e
         Read and execute commands from _f_i_l_e and return.  The
         search path $PATH is used to find the directory con-
         taining _f_i_l_e.
    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 [_a_r_g]
         Change the current directory to _a_r_g. The shell parame-
         ter $HOME is the default _a_r_g.
    eval [_a_r_g ...]
         The arguments are read as input to the shell and the
         resulting command(s) executed.
    exec [_a_r_g ...]
         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 argu-
         ments are given cause the shell input output to be
    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 [_n_a_m_e ...]
         The given names are marked for automatic export to the
         _e_n_v_i_r_o_n_m_e_n_t of subsequently-executed commands.  If no
         arguments are given then a list of exportable names is
    login [_a_r_g ...]
         Equivalent to `exec login arg ...'.
    newgrp [_a_r_g ...]
         Equivalent to `exec newgrp arg ...'.
    read _n_a_m_e ...
         One line is read from the standard input; successive
         words of the input are assigned to the variables _n_a_m_e
         in order, with leftover words to the last variable.
         The return code is 0 unless the end-of-file is encoun-
    readonly [_n_a_m_e ...]
         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 printed.
    set [-eknptuvx [_a_r_g ...]]
         -e If non interactive then exit immediately if a com-
            mand fails.
         -k All keyword arguments are placed in the environment
            for a command, not just those that precede the com-
            mand 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 exe-
         -  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.
         The positional parameters from $2...  are renamed $1...
         Print the accumulated user and system times for
         processes run from the shell.
    trap [_a_r_g] [_n] ...
         _A_r_g is a command to be read and executed when the shell
         receives signal(s) _n. (Note that _a_r_g 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 _a_r_g is absent then all trap(s) _n are reset to their
         original values.  If _a_r_g is the null string then this
         signal is ignored by the shell and by invoked commands.
         If _n is 0 then the command _a_r_g is executed on exit from
         the shell, otherwise upon receipt of signal _n as num-
         bered in _s_i_g_n_a_l(2).  _T_r_a_p with no arguments prints a
         list of commands associated with each signal number.
    umask [ _n_n_n ]
         The user file creation mask is set to the octal value
         _n_n_n (see _u_m_a_s_k(2)).  If _n_n_n is omitted, the current
         value of the mask is printed.
    wait [_n]
         Wait for the specified process and report its termina-
         tion 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 _s_t_r_i_n_g  If the -c flag is present then commands are read
               from _s_t_r_i_n_g.
    -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 descrip-
               tor 2.
    -i         If the -i flag is present or if the shell input
               and output are attached to a terminal (as told by
               _g_t_t_y) then this shell is _i_n_t_e_r_a_c_t_i_v_e. In this
               case the terminate signal SIGTERM (see _s_i_g_n_a_l(2))
               is ignored (so that `kill 0' does not kill an
               interactive shell) and the interrupt signal SIG-
               INT is caught and ignored (so that wait is inter-
               ruptable).  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.