sh(1)

NAME
sh, jsh - standard and job control shell and command interpreter

SYNOPSIS

/usr/bin/sh
   [-acefhikmnprstuvxP] [
argument]...

/usr/bin/jsh
  [-acefhikmnprstuvxP] [
argument]...

DESCRIPTION

The /usr/bin/sh utility is a command programming language that executes commands read from a terminal or a file.

The jsh utility is an interface to the shell that provides all of the functionality of sh and enables job control (see Job Control section below).

Arguments to the shell are listed in the Invocation section below.

  Definitions

A blank is a tab or a space. A name is a sequence of ASCII letters, digits, or underscores, beginning with a letter or an underscore. A parameter is a name, a digit, or any of the characters *, @, #, ?, -, $, and !.

  Invocation

If the shell is invoked through exec(2) and the first character of argument zero is -, commands are initially read from /etc/profile and from $HOME/.profile, if such files exist. Next, for interactive shells, commands are read from /etc/sh.shrc and from the file with a name that results from doing Parameter Substitution on the environment variable ENV if the file exists. Thereafter, commands are read as described below, which is also the case when the shell is invoked as /usr/bin/sh.

OPTIONS
The options below are interpreted by the shell on invocation only. Note: Unless the -c or -s option is specified, the first argument is assumed to be the name of a file containing commands, and the remaining arguments are passed as positional parameters to that command file:

-c string
    If the -c option is present commands are read from string. The remaining arguments become positional parameters starting at $0.

-i  If the -i option is present or if the shell input and output are attached to a terminal, this shell is interactive. In this case, TERMINATE is ignored (so that kill 0 does not kill an interactive shell) and INTERRUPT is caught and ignored (so that wait is interruptible). In all cases, QUIT is ignored by the shell.

-p  If the -p option is present, the shell does not set the effective user and group IDs to the real user and group IDs.

-r  If the -r option is present the shell is a restricted shell (see rsh(1M)).

-s  If the -s option is present or if no arguments remain, commands are read from the standard input. Any remaining arguments specify the positional parameters. Shell output (except for Special Commands) is written to file descriptor 2.

-version
    Print the current Bourne Shell version and exit.

Using + rather than - causes the related options to be turned off. The remaining options and arguments are described under the set command below.

USAGE

  Commands

A simple-command is a sequence of non-blank words separated by blanks. 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 (octal) 200+ status if it terminates abnormally. See signal.h(3HEAD) 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. The exit status of a pipeline is the exit status of the last command in the pipeline.

A list is a sequence of one or more pipelines separated by ;, &, &&, or ||, and optionally terminated by ; or &. Of these four symbols, ; and & have equal precedence, which is lower than that of && and ||. The symbols && and || also have equal precedence. A semicolon (;) causes sequential execution of the preceding pipeline, that is, the shell waits for the pipeline to finish before executing any commands following the semicolon. An ampersand (&) causes asynchronous execution of the preceding pipeline, that is, the shell does not wait for that pipeline to finish. The symbol && (||) causes the list following it to be executed only if the preceding pipeline returns a zero (non-zero) exit status. An arbitrary number of newlines can appear in a list, instead of semicolons, to delimit commands.

A command is either a simple-command or one of the following. Unless otherwise stated, 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 taken from the in word list. If in word ... is omitted, then the for command executes the do list once for each positional parameter that is set (see Parameter Substitution section below). Execution ends when there are no more words in the list.

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 (see File Name Generation section), except that a slash, a leading dot, or a dot immediately following a slash need not be matched explicitly.

if list then list [ elif list then list ] ... [ else list ] fi
The list following if is executed and, if it returns a zero exit status, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is zero, the list following the next then is executed. Failing that, the else list is executed. If no else list or then list is executed, then the if command returns a zero exit status.

while list do list done
until list do list done
A while command repeatedly executes the while list and, if the exit status of the last command in the list is zero, executes the do list; otherwise the loop terminates. If no commands in the do list are executed, then the while command returns a zero exit status; until can be used in place of while to negate the loop termination test.

(list)
Execute list in a sub-shell.

{ list;}
list is executed in the current (that is, parent) shell. The { must be followed by a space.

name () { list;}
Define a function which is referenced by name. The body of the function is the list of commands between { and }. The { must be followed by a space. Execution of functions is described below (see Execution section). The { and } are unnecessary if the body of the function is a command as defined above, under Commands.

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

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

  Comments Lines

A word beginning with # causes that word and all the following characters up to a newline to be ignored.

  Alias Substitution

After a token has been recognized, but before applying the grammatical rules, a resulting word that is identified as the command name of a simple command is examined whether it is an unquoted valid alias name. A valid alias name is replaced by the value of the alias. The shell prevents infinite alias loops by not expanding the same alias more than once for the same word.

Alias expansion is performed when the commands are read, not when they are executed.

Aliases can be used to redefine built-in commands but cannot be used to redefine the reserved words listed in the Commands section. Aliases can be created and listed with the alias command and removed with the unalias command.

POSIX compliant temporary alias definitions are not inherited by separate invocations of the shell or when interpreting scripts.

The Bourne Shell implements enhanced alias features beyond the POSIX alias definition. Enhanced alias features are disabled by default. They need to be turned on (see set command below) to make them operational. The following additional alias features are available:

persistent aliases
    If turned on by set -o globalaliases, persistent global aliases are automatically loaded by all interactive shells.

local aliases
    If turned on by set -o localaliases, persistent local aliases are automatically loaded by all interactive shells as a result of the cd command. Local aliases are specific to the current working directory. The local aliases definitions from the previous working directory are automatically disabled when the working directory is changed to a different directory. Local aliases have higher precedence than global aliases.

  Command Substitution

The shell reads commands from the string between two grave accents (``) and the standard output from these commands can be used as all or part of a word. Trailing newlines from the standard output are removed.

No interpretation is done on the string before the string is read, except to remove backslashes (\) used to escape other characters. Backslashes can be used to escape a grave accent (`) or another backslash (\) and are removed before the command string is read. Escaping grave accents allows nested command substitution. If the command substitution lies within a pair of double quotes (" ...` ...` ... "), a backslash used to escape a double quote (\") is removed. Otherwise, it is left intact.

If a backslash is used to escape a newline character (\newline), both the backslash and the newline are removed (see the later section on Quoting). In addition, backslashes used to escape dollar signs (\$) are removed. Since no parameter substitution is done on the command string before it is read, inserting a backslash to escape a dollar sign has no effect. Backslashes that precede characters other than \, `, ", newline, and $ are left intact when the command string is read.

  Parameter Substitution

The character $ is used to introduce substitutable parameters. There are two types of parameters, positional and keyword. If parameter is a digit, it is a positional parameter. Positional parameters can be assigned values by set. Keyword parameters (also known as variables) can be assigned values by writing:

name=value [ name=value ] ...

The evaluation of the assignments is done from the left to the right in this shell.

Pattern-matching is not performed on value. There cannot be a function and a variable with the same name.

${parameter}
    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 * or @, all the positional parameters, starting with $1, are substituted (separated by spaces). Parameter $0 is set from argument zero when the shell is invoked.

${parameter:-word}
    Use Default Values. If parameter is unset or null, the expansion of word is substituted; otherwise, the value of parameter is substituted.

${parameter:=word}
    Assign Default Values. If parameter is unset or null, the expansion of word is assigned to parameter. In all cases, the final value of parameter is substituted. Only variables, not positional parameters or special parameters, can be assigned in this way.

${parameter:?word}
    If parameter is set and is non-null, substitute its value; otherwise, print word and exit from the shell. If word is omitted, the message "parameter null or not set" is printed.

${parameter:+word}
    If parameter is set and is non-null, substitute word; otherwise substitute nothing.

In the above, word is not evaluated unless it is to be used as the substituted string, so that, in the following example, pwd is executed only if d is not set or is null:

echo  ${d:-`pwd`}

If the colon (:) is omitted from the above expressions, the shell only checks whether parameter is set or not.

The following parameters are automatically set by the shell.

#   The number of positional parameters in decimal.

n   The n-th positional parameter. The parameter name n is in the range from 1 to $#.

0   Parameter $0 is set from argument zero when the shell is invoked. If running a script, $0 is the name of the script.

*   All positional parameters starting from $1. "$*" expands to one argument that contains all positional parameters separated by spaces.

@   All positional parameters starting from $1. "$@" expands to $# arguments.

-   Flags supplied to the shell on invocation or by the set command.

?   The decimal value returned by the last synchronously executed command.

$   The process number of this shell.

!   The process number of the last background command invoked.

The following parameters are used by the shell. The parameters in this section are also referred to as environment variables.

HOME
    The default argument (home directory) for the cd command, set to the user's login directory by login(1) from the password file (see passwd(4)).

PATH
    The search path for commands (see Execution section below). If PATH is not set, it defaults to /usr/bin:.

CDPATH
    The search path for the cd command.

ENV This variable is used when and only when an interactive shell is invoked. It is subject to Parameter Substitution by the shell, and the resulting value is used as the pathname of a script that is executed when the shell is invoked. This file is typically used to define function definitions and transient alias definitions or to turn on persistent alias features or jobcontrol. The default value is $HOME/.shrc. If the result of the Parameter Substitution starts with /./ or ./ the file /etc/sh.shrc is not executed.

IGNOREEOF
    If set to on, the shell will not exit if a ^D is typed and the cursor is on an empty command line. The default is not to ignore EOF. IGNOREEOF is only supported if sh was compiled with support for history editing.

HISTORY
    The maximum number of lines to keep in the command history editor. The default is to keep 100 lines of command history. HISTORY is only supported if sh was compiled with support for history editing.

MAIL
    If this parameter is set to the name of a mail file and the MAILPATH parameter is not set, the shell informs the user of the arrival of mail in the specified file.

MAILCHECK
    This parameter specifies how often (in seconds) the shell checks for the arrival of mail in the files specified by the MAILPATH or MAIL parameters. The default value is 600 seconds (10 minutes). If set to 0, the shell checks before each prompt.

MAILPATH
    A colon-separated list of file names. If this parameter is set, the shell informs the user of the arrival of mail in any of the specified files. Each file name can be followed by % and a message that is e printed when the modification time changes. The default message is, you have mail.

OLDPWD
    The previous working directory, set by the cd, the pushd and the popd command. OLDPWD is not set before the first cd, pushd or popd command.

OPTARG
    This variable is used by getopts to store the argument if an option is using arguments.

OPTIND
    This variable is used by getopts as the index of the next argument to be processed.

PS1 Primary prompt string, by default " $ ".

PS2 Secondary prompt string, by default " > ".

PWD The present working directory set by the cd, the pushd and the popd command. For efficiency and to avoid NFS based hangs, PWD is not set before the first cd, dirs, pushd, popd, or pwd command. As it may have been imported with invalid content from the environment of the calling process, it is recommended to call pwd or cd . before depending on the content of PWD.

IFS Internal field separators, normally space, tab, and newline (see Blank Interpretation section).

SAVEHISTORY
    If set to on, the current history is saved in the file $HOME/.history when this shell exits. The default is not to save the history. SAVEHISTORY is only supported if sh was compiled with support for history editing.

SHACCT
    If this parameter is set to the name of a file writable by the user, the shell writes an accounting record in the file for each shell procedure executed.

SHELL
    When the shell is invoked, it scans the environment (see Environment section below) for this name.

TERM
    Used to determine the name of the terminal type. If this variable is unset or null, an unspecified default terminal type is used. TERM is only supported if sh was compiled with support for history editing.

TERMCAP
    This variable holds either a precompiled termcap entry or the pathname to be used to find a termcap database file. If it holds a precompiled entry that does not match the TERM environment, the termcap database is parsed as if the TERMCAP environment is not set. TERMCAP is automatically exported after filling it with a precompiled entry to speed up termcap based applications. TERMCAP is only supported if sh was compiled with support for history editing.

TERMPATH
    If TERMCAP is empty or not set, then the TERMPATH environment is scanned for pathnames of files that contain a termcap database. It holds a list of filenames separated by colons or spaces (i.e., ":" or " "). If the TERMPATH symbol is not set, the files $HOME/.termcap and /etc/termcap are scanned in that order. If a pathname in TERMPATH does not start with a slash ("/"), then the HOME environment is prepended to the name. TERMPATH is only supported if sh was compiled with support for history editing.

See environ(5) for descriptions of the following environment variables that affect the execution of sh: LANG, LC_ALL, LC_CTYPE and LC_MESSAGES.

The shell gives default values to PATH, PS1, PS2, MAILCHECK, HISTORY, and IFS. Default values for HOME and MAIL are set by login(1).

  Blank Interpretation

After parameter and command substitution, the 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 removed.

The IFS parameter is applied to any unquoted word. Thus.

    IFS=X
    echoXfoo

executes the `echo' command with the argument `foo'.

  Input/Output Redirection

A command's input and output can be redirected using a special notation interpreted by the shell. The following can appear anywhere in a simple-command or can precede or follow a command and are not passed on as arguments to the invoked command. Note: Parameter and 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, it is created; otherwise, it is truncated to zero length.

>>word
    Use file word as standard output. If the file exists, output is appended to it by first seeking to the EOF. Otherwise, the file is created.

<>word
    Open file word for reading and writing as standard input.

<<[-]word
    After parameter and command substitution is done on word, the shell input is read up to the first line that literally matches the resulting word, or to an EOF. If, however, the hyphen (-) is appended to <<:

        1.  leading tabs are stripped from word before the shell input is read (but after parameter and command substitution is done on word);

        2.  leading tabs are stripped from the shell input as it is read and before each line is compared with word; and

        3.  shell input is read up to the first line that literally matches the resulting word, or to an EOF.
    If any character of word is quoted (see Quoting section later), no additional processing is done to the shell input. If no characters of word are quoted:

        1.  parameter and command substitution occurs;

        2.  (escaped) \newlines are removed; and

        3.  \ must be used to quote the characters \, $, and `.
    The resulting document becomes the standard input.

<&digit
    Use the file associated with file descriptor digit as standard input. Similarly for the standard output using >&digit.

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

If any of the above is preceded by a digit, the file descriptor which is associated with the file is that specified by the digit (instead of the default 0 or 1). For example:

... 2>&1

associates file descriptor 2 with the file currently associated with file descriptor 1.

The order in which redirections are specified is significant. The shell evaluates redirections left-to-right. For example:

... 1>xxx 2>&1

first associates file descriptor 1 with file xxx. It associates file descriptor 2 with the file associated with file descriptor 1 (that is, xxx). If the order of redirections were reversed, file descriptor 2 would be associated with the terminal (assuming file descriptor 1 had been) and file descriptor 1 would be associated with file xxx.

Using the terminology introduced on the first page, under Commands, if a command is composed of several simple commands, redirection is evaluated for the entire command before it is evaluated for each simple command. That is, the shell evaluates redirection for the entire list, then each pipeline within the list, then each command within each pipeline, then each list within each command.

If a command is followed by & and job control (see set -m) is not active, 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.

  File Name Generation

Before a command is executed, each command word is scanned for the characters *, ?, and [. If one of these characters appears 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, the word is left unchanged. The character . at the start of a file name or immediately following a /, as well as the character / itself, must be matched explicitly.

*   Matches any string, including the null string.

?   Matches any single character.

[...]
    Matches any one of the enclosed characters. A pair of characters separated by - matches any character lexically between the pair, inclusive. If the first character following the opening [ is a !, any character not enclosed is matched.

Notice that all quoted characters (see below) must be matched explicitly in a filename.

  Quoting

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

; & ( ) | ^ < > newline space tab

A character can be quoted (that is, made to stand for itself) by preceding it with a backslash (\) or inserting it between a pair of quote marks ('' or ""). During processing, the shell can quote certain characters to prevent them from taking on a special meaning. Backslashes used to quote a single character are removed from the word before the command is executed. The pair \newline is removed from a word before command and parameter substitution.

All characters enclosed between a pair of single quote marks (''), except a single quote, are quoted by the shell. Backslash has no special meaning inside a pair of single quotes. A single quote can be quoted inside a pair of double quote marks (for example, "'"), but a single quote can not be quoted inside a pair of single quotes.

Inside a pair of double quote marks (""), parameter and command substitution occurs and the shell quotes the results to avoid blank interpretation and file name generation. If $* is within a pair of double quotes, the positional parameters are substituted and quoted, separated by quoted spaces ("$1 $2 ..."). However, if $@ is within a pair of double quotes, the positional parameters are substituted and quoted, separated by unquoted spaces ("$1""$2" ... ). \ quotes the characters \, `, , (comma), and $. The pair \newline is removed before parameter and command substitution. If a backslash precedes characters other than \, `, , (comma), $, and newline, then the backslash itself is quoted by the shell.

  Prompting

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, the secondary prompt (that is, the value of PS2) is issued.

  Environment

The environment (see environ(5)) is a list of name-value pairs that is passed to an executed program in the same way as a normal argument list. 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. If the user modifies the value of any of these parameters or creates new parameters, none of these affects the environment unless the export command is used to bind the shell's parameter to the environment (see also set -a). A parameter can be removed from the environment with the unset command. The environment seen by any executed command is thus composed of any unmodified name-value pairs originally inherited by the shell, minus any pairs removed by unset, plus any modifications or additions, all of which must be noted in export commands.

The environment for any simple-command can be augmented by prefixing it with one or more assignments to parameters. Thus:

TERM=450 command

and

(export TERM; TERM=450; command)

are equivalent as far as the execution of command is concerned if command is not a Special Command. If command is a Special Command, then

TERM=450 command

modifies the TERM variable in the current shell.

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

echo a=b  c
a=b  c
set  -k
echo a=b  c
c

  Signals

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, with the exception of signal 11 (but see also the trap command below).

  Execution

Each time a command is executed, the command substitution, parameter substitution, blank interpretation, input/output redirection, and filename generation listed above are carried out. If the command name matches the name of a defined function, the function is executed in the shell process (note how this differs from the execution of shell script files, which require a sub-shell for invocation). If the command name does not match the name of a defined function, but matches one of the Special Commands listed below, it is executed in the shell process.

The positional parameters $1, $2, ... are set to the arguments of the function. If the command name matches neither a Special Command nor the name of a defined function, a new process is created and an attempt is made to execute the command via exec(2).

The shell parameter PATH defines the search path for the directory containing the command. Alternative directory names are separated by a colon (:). The default path is /usr/bin:. The current directory is specified by a null path name, which can appear immediately after the equal sign, between two colon delimiters anywhere in the path list, or at the end of the path list. If the command name contains a / 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 sub-shell is spawned to read it. A parenthesized command is also executed in a sub-shell.

The location in the search path where a command was found is remembered by the shell (to help avoid unnecessary execs later). If the command was found in a relative directory, its location must be re-determined whenever the current directory changes. The shell forgets all remembered locations whenever the PATH variable is changed or the hash -r command is executed (see below).

  Special Commands

Input/output redirection is now permitted for these commands. File descriptor 1 is the default output location. When Job Control is enabled, additional Special Commands are added to the shell's environment (see Job Control section below).

:

    No effect; the command does nothing. A zero exit code is returned.

. filename

    Read and execute commands from filename and return. The search path specified by PATH is used to find the directory containing filename.

[ [expr] ]

See test builtin below.

alias [ options ] [alias-name[=value]...]

    The alias command creates, redefines or lists existing alias definitions. An alias definition provides a string value that replaces a command name when it is encountered on the command line.

    The alias command in the Bourne Shell supports temporary aliases (POSIX aliases) that affect only the current execution environment as well as persistent aliases that affect all interactive shells that are called after a persistent alias definition was entered or modified.

    An argument in the form alias-name causes alias to list the related alias on stdout. An argument in the form alias-name=value causes alias to define or redefine an alias or to push an alias definition on top of an old one. If no argument was given, alias lists all current alias definitions.

    Alias definitions must be written with appropriate quoting.

    When operating on temporary aliases (i.e. when neither -g nor -l have been specified), the alias command always pushes new definitions on top of older ones. This makes such alias definitions temporary in the global aliases name space by default, as required by the POSIX standard. The following options may be used to modify operation:

    -a  Define an alias definition that is expanded on all arguments of a command line and not only for command names. Use with care.

    -e  List the everlasting version of the persistent alias definitions instead of listing the currently active definitions that may have been pushed on top of the persistent definitions.

    -g  Define or list persistent global aliases that are stored in the file $HOME/.globals and read by interactive shells. When defining an alias with -g in effect, alias by default modifies the current top level definition for global aliases. If there was no push operation before on the related alias, the current definition is made persistent by writing the definitions to $HOME/.globals. The option -g is not permitted if persistent global aliases are disabled (see set command below).

    -l  Define or list persistent directory local aliases that are stored in the file .locals in the current directory and read by interactive shells. When defining an alias with -l in effect, alias by default modifies the current top level definition for local aliases. If there was no push operation before on the related alias, the current definition is made persistent by writing the definitions to .locals in the current directory. The option -l is not permitted if persistent local aliases are disabled (see set command below).

    -p  When defining or redefining aliases, enforce a push operation even if the option -g or -l has been specified. In push mode, the new alias definition is pushed temporarily on top of existing definitions instead of modifying the current definition.

        When listing aliases, this option implements compatibility to bash/ksh93 and outputs aliases in a form that can be used as input to the shell to recreate the current aliases. With -p in effect in list mode, the persistent definition and all pushed definitions are listed; otherwise only the current active definitions are listed.

    -r  Reload persistent aliases after removing all current aliases. If persistent aliases are disabled, the effect is the same as with calling unalias -a. No arguments are allowed with this option.

    --raw
        Output the listing in the raw format that is used in the persistent definition files $HOME/.globals and .locals. This increases readability as the quoting needed for defining an alias with the alias command is omitted.

    Aliases are often used together with the dosh builtin in order to run small parameterized shell scripts.

alloc

    In case sh has been compiled with storage debugging support, the alloc command prints information about the curren state of the storage subsystem; otherwise alloc is a dummy command. The alloc command was not supported in older versions of sh.

bg [%jobid ...]

    When Job Control is enabled, the bg command is added to the user's environment to manipulate jobs. Resumes the execution of a stopped job in the background. If %jobid is omitted the current job is assumed. (See Job Control section below for more detail.)

break [ n ]

    Exit from the enclosing for or while loop, if any. If n is specified, break n levels.

cd [ argument ]

    Change the current directory to argument. The shell parameter HOME is the default argument. The shell parameter CDPATH defines the search path for the directory containing argument. Alternative directory names are separated by a colon (:). The default path is <null> (specifying the current directory). Note: The current directory is specified by a null path name, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If argument begins with a / the search path is not used. Otherwise, each directory in the path is searched for argument.

    The previous working directory is kept in the shell parameter OLDPWD, the new working directory is kept in the shell parameter PWD. The top of the directory stack is replaced by the new working directory.

chdir [ dir ]

    chdir changes the shell's working directory to directory dir. If no argument is given, change to the home directory of the user. If dir is a relative pathname not found in the current directory, check for it in those directories listed in the CDPATH variable. If dir is the name of a shell variable whose value starts with a /, change to the directory named by that value.

continue [ n ]

    Resume the next iteration of the enclosing for or while loop. If n is specified, resume at the n-th enclosing loop.

dirs

    Print the content of the directory stack. The top of the stack is the leftmost element which has the logical offset 0. The next element to the right has the logical offset 1. The logical offset of a directory may be used as argument to the pushd and the popd command. If there is no directory stack, the result is the same as with calling pwd. The dirs command was not supported in older versions of sh.

dosh command_string [[ command_name ] [ args ]]

    The dosh command executes commands from command_string with new positional parameters as if the commands in command_string were read from a shell script. If the optional parameter command_name is present, it replaces the positional parameter $0. Additional arguments are set up as positional parameters for the commands in command_string, starting with $1. The dosh command thus behaves like sh -c command_string, but does not launch a new shell. Calling return returns from command_string as if returning from a function. Calling exit does not exit the shell but returns from the command_string. The dosh command is often used together with aliases. The dosh command was not supported in older versions of sh.

echo [ arguments ... ]

    The words in arguments are written to the shell's standard output, separated by space characters. See echo(1) for fuller usage and description.

    If /usr/ucb appears before any other system directory in PATH and the first argument is -n, echo does not print a final new-line and does not interpret backslashed escape characters. Otherwise, -n is treated as a normal argument. If the $SYSV3 variable is set in the initial environment passed to the shell, the -n argument is also interpreted, but escape sequences are processed as usual.

    The following character sequences are recognized within any of the arguments:

    \a  Alert character.
    \b  Backspace.
    \c  Print line without new-line. All characters following the \c in the argument are ignored.
    \f  Form-feed.
    \n  New-line.
    \r  Carriage return.
    \t  Tab.
    \v  Vertical tab.
    \\  Backslash.
    \0n Where n is the 8-bit character whose ASCII code is the 1-, 2- or 3-digit octal number representing that character.

eval [ argument ... ]

    The arguments are read as input to the shell and the resulting command(s) executed.

exec [ argument ... ]

    The command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments can appear and, if no other arguments are given, cause the shell input/output to be modified.

exit [ n ]

    Causes the calling shell or shell script to exit with the exit status specified by n. If n is omitted the exit status is that of the last command executed (an EOF also causes the shell to exit.)

export [ name ... ]

    The given names are marked for automatic export to the environment of subsequently executed commands. If no arguments are given, variable names that have been marked for export during the current shell's execution are listed. (Variable names exported from a parent shell are listed only if they have been exported again during the current shell's execution.) Function names are not exported.

false

    The false builtin does nothing. A non-zero exit code is returned.

fg [%jobid ...]

    When Job Control is enabled, the fg command is added to the user's environment to manipulate jobs. This command resumes the execution of a stopped job in the foreground and also moves an executing background job into the foreground. If %jobid is omitted, the current job is assumed. (See Job Control section below for more detail.)

getopts optstring name [arg...]

    Use in shell scripts to support command syntax standards (see Intro(1)). This command parses positional parameters and checks for legal options. See getoptcvt(1) for usage and description.

    The getopts builtin command parses its args or the global args of the current shell, using optstring as option definition. Each time it is invoked, it places the next option into the variable name and the index of the next argument to be processed into OPTIND. Whenever the shell or a shell script is invoked, OPTIND is initialized to 1. Calling getopts repeatedly causes one option to be retrieved per call.

    When an option requires an option-argument, getopts places it in the shell variable OPTARG.

    If an illegal option is encountered, ? is placed in name. If optstring starts with a colon and a required option-argument is missing, a colon is placed in name.

    When the end of options is encountered, getopts exits with a non-zero exit status. The special arg -- can be used to delimit the end of the options.

    optstring must contain the option letters the command using getopts recognizes. If a letter is followed by a colon, the option is expected to have an argument, or group of arguments, which must be separated from it by white space.

    Unless optstring starts with a colon, getopts prints an error message on the standard error when it encounters an option letter not included in optstring.

    getopts supports one or more long options as an alias to a short option. You must enclose each long option equivalent in parentheses, as follows:

      getopts "f:(file)(input-file)o:(output-file)"

    In the above example, both --file and --input-file are the equivalent of -f, and --output-file is the equivalent of -o.

hash [ -r ] [ name ... ]

    For each name, the location in the search path of the command specified by name is determined and remembered by the shell. The -r option causes the shell to forget all remembered locations. If no arguments are given, information about remembered commands is presented. Hits is the number of times a command has been invoked by the shell process. Cost is a measure of the work required to locate a command in the search path. If a command is found in a "relative" directory in the search path, after changing to that directory, the stored location of that command is recalculated. Commands for which this are done are indicated by an asterisk (*) adjacent to the hits information. Cost is incremented when the recalculation is done.

history

    Print the current command history. The history command is only supported if sh was compiled with support for history editing. The history command was not supported in older versions of sh.

jobs [-p|-l] [%jobid ...]
jobs -x command [arguments]

    Reports all jobs that are stopped or executing in the background. If %jobid is omitted, all jobs that are stopped or running in the background are reported. (See Job Control section below for more detail.)

kill [ -sig ] %job ...
kill -l

    Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in signal.h(3HEAD) stripped of the prefix "SIG" with the exception that SIGCHD is named CHLD). If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process is sent a CONT (continue) signal if it is stopped. The argument job can be the process id of a process that is not a member of one of the active jobs. See Job Control section below for a description of the format of job. In the second form, kill -l, the signal numbers and names are listed. (See kill(1)).

login [ argument ... ]

    Equivalent to `exec login argument....' See login(1) for usage and description.

map
map -r
map map_from map_to [ comment ]
map -u map_from

    Handle history editor input mapping. Input mapping in the history editor is automatically managed via TERMCAP for the cursor keys and via manual maps in the file $HOME/.bshmap. The map command is only supported if sh was compiled with support for history editing.

    If the map command is called without arguments, it prints the current input mapping.

    If map is called with -r, all current mappings are removed and the default mapping is reloaded from TERMCAP and $HOME/.bshmap. Call map -r after changing TERM, TERMCAP or TERMPATH or when a change was made in the file $HOME/.bshmap.

    It map is called with two or three arguments, a new mapping is set up. The parameters map_from and map_to may need quoting to be correctly passed to the mapping engine.

    Call map -u map_from to unmap an existing mapping. The parameter map_from needs quoting for both the input mapper and the shell to be correctly passed to the mapping engine.

    For more information and for escape sequences known by the mapper see the section History Editing Input Mappings below. The map command was not supported in older versions of sh.

newgrp [ argument ]

    Equivalent to exec newgrp argument. See newgrp(1) for usage and description.

popd [ -offset ]

    Calling popd without argument removes the current top directory stack element from the directory stack and then performs a cd to the new top directory stack element. Calling popd with an offset argument removes the current the top directory stack element from the directory stack, them removes the directory stack element named by offset from the current directory stack, makes it the new top directory stack element and performs a cd to this directory. If the new directory stack has more than one element, it is printed. See dirs for an explanation of offset. The popd command was not supported in older versions of sh.

pushd [ name ]
pushd [ -offset ]

    The pushd command is similar to the cd command, but it keeps the previous working directory on the directory stack. If -offset is used instead of a directory name, it exchanges the content of the top directory stack element with the directory stack element named by offset and then performs a cd to the new top directory stack element. If the new directory stack has more than one element, it is printed. See dirs for an explanation of offset. The pushd command was not supported in older versions of sh.

pwd

    Print the current working directory. See pwd(1) for usage and description. The current working directory is kept in the shell parameter PWD.

read [ -r ] name ...

    One line is read from the standard input and, using the internal field separator, IFS (normally space or tab), to delimit word boundaries, the first word is assigned to the first name, the second word to the second name, and so forth, with leftover words assigned to the last name. Lines can be continued using \newline. Characters other than newline can be quoted by preceding them with a backslash. These backslashes are removed before words are assigned to names, and no interpretation is done on the character that follows the backslash. The return code is 0, unless an EOF is encountered.

    -r  Do not treat a backslash character in any special way. Consider each backslash to be part of the input line. The option -r was not supported in older versions of sh.

readonly [ name ... ]

    The given names are marked readonly and the values of the these names can not be changed by subsequent assignment. If no arguments are given, a list of all readonly names is printed.

repeat [ -c count ] [ -d delay ] command [ args ]

    The command command is executed repeatedly as if it was called via eval. If the -c option is present, command is repeated count times, otherwise execution is repeated forever. If the -d option is present, sh waits delay seconds before command is executed again, otherwise there is no delay between executions. The repeat command was not supported in older versions of sh.

return [ n ]

    Causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command executed.

savehistory

    Save the current history in the file $HOME/.history. The savehistory command was not supported in older versions of sh.

set [ -aefhkmntuvxP [ argument ... ] ]

    -a  Mark variables which are modified or created for export.

    -e  Exit immediately if a command exits with a non-zero exit status.

    -f  Disable file name generation.

    -h  Locate and remember function commands as functions are defined (function commands are normally located when the function is executed).

    -k  All keyword arguments are placed in the environment for a command, not just those that precede the command name.

    -m  Switch job control mode on.

    -n  Read commands but do not execute them. Setting -n in an interactive shell is ignored as this could not be undone and the shell could not even be terminated anymore.

    -t  Exit after reading and executing one command.

    -o [option]
        If option is not specified, list the current option setting to stdout; when invoked with +o instead of -o, the output is written in a format that is suitable to reinput to the shell to restore the current setting. When invoked with +o and with option argument, the related option is cleared. The +o option may be repeated to enable or disable multiple options. The value of option must be one of the following:

        allexport
            Equivalent to -a.
        aliasowner=name
            Set an alternate trusted owner for the files $HOME/.globals and .locals. By default, the shell ignores alias files if they are not owned by the current shell user. This option allows to set up an alternate file owner that is accepted. Setting the alternate owner to the empty string disables the feature.
        errexit
            Equivalent to -e.
        globalaliases
            Enables/disables persistent global aliases that are read from the file $HOME/.globals. Changing the state for this option first removes all current global aliases. If the new state is on, the persistent global aliases are loaded.
        hashall
            Equivalent to -h.
        interactive
            Equivalent to -i.
        keyword
            Equivalent to -k.
        localaliases
            Enables/disables persistent directory local aliases that are read from the file .locals in the current directory. Local aliases are specific to the current working directory. Changing the state for this option first removes all current local aliases. If the new state is on, the persistent local aliases are loaded from the current directory.
        monitor
            Equivalent to -m.
        noexec
            Equivalent to -n.
        noglob
            Equivalent to -f.
        nounset
            Equivalent to -u.
        onecmd
            Equivalent to -t.
        pfsh
            Equivalent to -P.
        privileged
            Equivalent to -p.
        restricted
            Equivalent to -r.
        stdin
            Equivalent to -s.
        verbose
            Equivalent to -v.
        ved Allow shell command line editing using the built in ved editor.
        vi  Allow shell command line editing using the built in vi editor. The Bourne Shell currently does not allow to set the vi mode for any type of terminal.
        xtrace
            Equivalent to -x.

    -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.

    -P  Switch profile mode on. In this mode, the shell runs privilleged programs automatically in privilleged mode. See pfexec(1) for further information. This feature is only supported on Solaris 10 and above. The option -P was not supported in older versions of sh.

    -   Clear the -v and -x option.

    --  Stop option processing. Further parameters are handled as normal args even when they start with a -.

    Using + rather than - causes these flags to be turned off. These flags can also be used upon invocation of the shell. The flags -c, -i, -p, -r and -s can only be set upon invocation of the shell, they cannot be modified using the set command. The current set of flags can be found in $-. The remaining arguments are positional parameters and are assigned, in order, to $1, $2, ... If no arguments are given, the values of all names are printed.

shift [ n ]

    The positional parameters from $n+1 ... are renamed $1 ... . If n is not given, it is assumed to be 1.

stop pid ...

    Halt execution of the process number pid. (see ps(1)).

suspend

    Stops the execution of the current shell (but not if it is the login shell).

test [expr]

    Evaluate conditional expressions. See test(1) for usage and description. If the value of the expression expr, is true then test returns zero exit status; otherwise, a non zero exit status is returned. test returns a non zero exit status if there are no arguments.

    The following primaries are used to evaluate a condition:

    -b file
        True if file exists and is a block special file.
    -c file
        True if file exists and is a character special file.
    -d file
        True if file exists and is a directory.
    -f file
        True if file exists and is a regular file. Alternatively, if Bourne Shell users specify /usr/ucb before /usr/bin in their PATH environment variable, then test returns true if file exists and is (not-a-directory).
    -g file
        True if file exists and its set group ID flag is set.
    -h file
        True if file exists and is a symbolic link.
    -k file
        True if file exists and has its set sticky bit set.
    -L file
        True if file exists and is a symbolic link.
    -n string
        True if the length of string is non-zero.
    -p file
        True if file exists and is a named pipe (FIFO).
    -r file
        True if file exists and is readable.
    -s file
        True if file exists and has a size greater then zero.
    -t [file-descriptor]
        True if the file whose file descriptor number is file-descriptor is open and is associated with a terminal. If file-descriptor is not specified, 1 is used as a default value.
    -u file
        True if file exists and its set user ID flag is set.
    -w file
        True if file exists and is writable.
    -x file
        True if file exists and is executable. True indicates only that the execute flag is on. If file is a directory, true indicates that file can be searched.
    -z string
        True if the length of string is zero.

    string
        True if string is not the null string.
    s1 = s2
        True if the strings s1 and s2 are identical.
    s1 != s2
        True if the strings s1 and s2 are not identical.
    n1 -eq n2
        True if the integers n1 and n2 are algebraically equal.
    n1 -ne n2
        True if the integers n1 and n2 are not algebraically equal.
    n1 -gt n2
        True if the integer n1 is algebraically greater than the integer n2.
    n1 -ge n2
        True if the integer n1 is algebraically greater or equal to the integer n2.
    n1 -lt n2
        True if the integer n1 is algebraically less than the integer n2.
    n1 -le n2
        True if the integer n1 is algebraically less or equal to the integer n2.

    The primaries above may be combined with the following operators:

    ( expr )
        Bracketing to group precedence.
    !   unary negation operator.
    -a  binary and operator. The -a binary primary is left associative and has higher precedence than the -o binary primary.
    -o  binary or operator. The -o binary primary is left associative.

times

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

trap [ [argument] n [ n2 ... ]]

    The command argument is to be read and executed when the shell receives numeric or symbolic signal(s) (n). (Note: argument is scanned once when the trap is set and once when the trap is taken.) Trap commands are executed in order of signal number or corresponding symbolic names. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. An attempt to trap on signal 11 (memory fault) produces an error. If argument is absent, all trap(s) n are reset to their original values. If argument is the null string, this signal is ignored by the shell and by the commands it invokes. If n is 0, the command argument is executed on exit from the shell. The trap command with no arguments prints a list of commands associated with each signal number.

true

    The true builtin does nothing. A zero exit code is returned.

type [ name ... ]

    For each name, indicate how it would be interpreted if used as a command name.

ulimit [ [-HS] [-a | -cdflmnstuv] ]
ulimit [ [-HS] [-c|-d|-f|-l|-m|-n|-s|-t|-u|-v] ] limit

    ulimit prints or sets hard or soft resource limits. These limits are described in getrlimit(2).

    If limit is not present, ulimit prints the specified limits. Any number of limits can be printed at one time. The -a option prints all limits.

    If limit is present, ulimit sets the specified limit to limit. The string unlimited requests that the current limit, if any, be removed. Any user can set a soft limit to any value less than or equal to the hard limit. Any user can lower a hard limit. Only a user with appropriate privileges can raise or remove a hard limit. See getrlimit(2).

    The -H option specifies a hard limit. The -S option specifies a soft limit. If neither option is specified, ulimit sets both limits and print the soft limit.

    The following options specify the resource whose limits are to be printed or set. If no option is specified, the file size limit is printed or set.

    -c  maximum core file size (in 512-byte blocks)

    -d  maximum size of data segment or heap (in kbytes)

    -f  maximum file size (in 512-byte blocks)

    -l  maximum size of locked memory (in kbytes)

    -m  maximum resident set size (in kbytes)

    -n  maximum file descriptor plus 1

    -s  maximum size of stack segment (in kbytes)

    -t  maximum CPU time (in seconds)

    -u  maximum number of child processes

    -v  maximum size of virtual memory (in kbytes)

    Not all resources are supported on all platforms.

    Run the sysdef(1M) command to obtain the maximum possible limits for your system. The values reported are in hexadecimal, but can be translated into decimal numbers using the bc(1) utility. See swap(1M).)

    As an example of ulimit, to limit the size of a core file dump to 0 Megabytes, type the following:

    ulimit -c 0

umask [ -S ] [ mask ]

    The user file-creation mask is set to mask (see umask(1)). The mask may either be an octal numner or a symbolic notation (see chmod(1)). If the symbolic notation for mask starts with a - sign, it must be preceded with -- to keep it from being interpreted as an option. The command umask -- -w sets the file-creation mask so that subsequently created files have all their write bits cleared.

    If mask is omitted, the current value of the mask is printed.

    Do not use a symbolic mask or -S in Bourne Shell scripts that should be portable to older revisions.

    -S  Print the current file-creation mask in symbolic form. The output is suitable as argument for the umask command.

    The symbolic mode was not supported in older versions of sh.

unalias [ options ] [alias-name...]

    The unalias command removes existing alias definitions.

    The unalias command in the Bourne Shell supports temporary aliases (POSIX aliases) that affect only the current execution environment as well as persistent aliases that affect all interactive shells that are called after a persistent alias definition was entered or modified.

    When operating on temporary aliases (i.e. when neither -g nor -l have been specified), all alias definitions for a specified alias-name are popped from the existing global definitions. No alias definition for the specified alias-name remains active, but the file with persistent alias definitions is not touched. This makes unalias compatible to the POSIX standard and able to support persistent aliases at the same time. The following options may be used to modify operation:

    -a  Remove all alias definitions from the current shell execution environment. No arguments are permitted with this option. As the persistent definitions are not touched, the persistent aliases may be restored by calling alias -r.

    -g  Pop a single alias definition for alias-name from the global aliases. If the related alias definition is the last for alias-name (use alias -p -g alias-name to verify), remove it from the persistent global aliases that are stored in the file $HOME/.globals and read by interactive shells.

    -l  Pop a single alias definition for alias-name from the local aliases. If the related alias definition is the last for alias-name (use alias -p -l alias-name to verify), remove it from the persistent local aliases that are stored in the file .locals in the current directory and read by interactive shells.

    -p  When removing aliases, enforce a pop all operation even if the option -g or -l has been specified. In pop all mode, all alias definitions for a specified alias-name are popped from the existing definitions. No alias definition for the specified alias-name remains active, but the file with persistent alias definitions is not touched.

unset [ name ... ]

    For each name, remove the corresponding variable or function value. The variables PATH, PS1, PS2, MAILCHECK, and IFS cannot be unset.

wait [ n ]

    Wait for your background process whose process id is n and report its termination status. If n is omitted, all your shell's currently active background processes are waited for and the return code is zero.

  Job Control (jsh)

When the shell is invoked as jsh, Job Control is enabled in addition to all of the functionality described previously for sh. Typically, Job Control is enabled for the interactive shell only. Non-interactive shells typically do not benefit from the added functionality of Job Control.

With Job Control enabled, every command or pipeline the user enters at the terminal is called a job. All jobs exist in one of the following states: foreground, background, or stopped. These terms are defined as follows:

    1.  A job in the foreground has read and write access to the controlling terminal.

    2.  A job in the background is denied read access and has conditional write access to the controlling terminal (see stty(1)).

    3.  A stopped job is a job that has been placed in a suspended state, usually as a result of a SIGTSTP signal (see signal.h(3HEAD)).

Every job that the shell starts is assigned a positive integer, called a job number which is tracked by the shell and is used as an identifier to indicate a specific job. Additionally, the shell keeps track of the current and previous jobs. The current job is the most recent job to be started or restarted. The previous job is the first non-current job.

The acceptable syntax for a Job Identifier is of the form:

%jobid

where jobid can be specified in any of the following formats:

% or +
    For the current job.

-   For the previous job.

?<string>
    Specify the job for which the command line uniquely contains string.

n   For job number n.

pref
    Where pref is a unique prefix of the command name. For example, if the command ls -l name were running in the background, it could be referred to as %ls. pref cannot contain blanks unless it is quoted.

When Job Control is enabled, the following commands are added to the user's environment to manipulate jobs:

bg [%jobid ...]

    Resumes the execution of a stopped job in the background. If %jobid is omitted the current job is assumed.

fg [%jobid ...]

    Resumes the execution of a stopped job in the foreground, also moves an executing background job into the foreground. If %jobid is omitted the current job is assumed.

jobs [-p|-l] [%jobid ...]
jobs -x command [arguments]

    Reports all jobs that are stopped or executing in the background. If %jobid is omitted, all jobs that are stopped or running in the background is reported. The following options modify/enhance the output of jobs:

    -l  Report the process group ID and working directory of the jobs.

    -p  Report only the process group ID of the jobs.

    -x  Replace any jobid found in command or arguments with the corresponding process group ID, and then execute command passing it arguments.

kill [ -signal ] %jobid

    Builtin version of kill to provide the functionality of the kill command for processes identified with a jobid.

stop %jobid ...

    Stops the execution of a background job(s).

suspend

    Stops the execution of the current shell (but not if it is the login shell).

wait [%jobid ...]

    wait builtin accepts a job identifier. If %jobid is omitted wait behaves as described above under Special Commands.

  Command History Editing

If compiled with -DINTERACTIVE, the Bourne Shell includes a command line history and a command line editor. The behavior of the command line editor is the same as introduced in 1984 with bsh(1) and has been inspired by the behavior of the editor ved(1).

The history is implemented as limited ring buffer. The size of the ring buffer is in HISTORY. If HISTORY is unset or set to 0, the current command line history is lost and command line editing is only supported on the current line and this line is not kept in the history. Command line editing may be turned off completely by issuing the command `set +o ved'. The existing history is not affected by turning off the command line editor.

Command lines from the existing history may be retrieved with the cursor keys (Cursor up and Cursor down). Typing <CR> or <LF> executes the command on the line with the cursor.

Each new command is appended to the end of the history. If the maximum size of the history is reached, the oldest command is removed. Identical commands are avoided as far as possible. If an command is entered that is already in the history, it is moved to the end of the history.

  History Editing Commands

The following commands allow to edit a command line:

^H  Move cursor one character to the left.

^F  Move cursor one character to the right.

^D  Erase the character under the cursor.

DEL Erase one character to the left of the cursor.

^U  Erase the whole line.

^^  Quote next character.

CR  Finish current line and execute it.

NL  Finish current line and execute it.

TAB Do file name completion for the word to the left side of the cursor. If more than one file matches the current partial filename, a BEEP is generated. Typing a second TAB displays a list of matching names.

ESC- ^H
    Move cursor one word to the left.

ESC- ^F
    Move cursor one word to the right.

ESC- ^D
    Erase the word under the cursor to the right.

ESC- DEL
    Erase the word to the left of the cursor.

The following commands are available to navigate within the history:

^P  Move cursor to the previous history line.

^N  Move cursor to the next history line.

ESC- ^P
    Search backwards in the history. The user is prompted for a search pattern. The previous search string is kept and may be edited. To enter a new search string, first type ^U.

ESC- ^N
    Search forwards in the history. The user is prompted for a search pattern. The previous search string is kept and may be edited. To enter a new search string, first type ^U.

ESC- p
    Search backwards in the history. Clear the old search pattern first.

ESC- n
    Search forwards in the history. Clear the old search pattern first.

ESC- CR
    Return to the history line that was in use before the last search command.

Other characters are inserted into the command line text. Characters that are listed above as being edit command characters need to be quoted using the quote character ^^. If a line is entered via CR or NL, the current position of the cursor is irrelevant.

The command line editor remembers the cursor position for each command line in the history during the lifetime of the shell process.

  History Editing Input Mappings

The command line history editor maps input from the terminal into mapped text before it is interpreted by the editor. If a match is found on the input from the terminal, the related input text is directly replaced by it's replacement string. A mapping may be prevented by typing the map quote character which is the nul character (^@), directly before the matching text is entered.

At startup (directly before the first shell command prompt is shown), the command line history editor first tries to initialize the terminal setup using the variables HOME, TERM, TERMCAP and TERMPATH. Then it tries to read the file $HOME/.bshmap to retrieve additional mappings.

If TERM is not set, the mapper establishes standard mappings for the cursor keys assuming an ANSI-compatible terminal.

Each line in the file $HOME/.bshmap has the following structure:

map_from:map_to:comment

map_from is the string that is going to be replaced in the input, map_to is the string replacement and comment is optional comment that is not used for mapping itself. If both map_from and map_to are empty, the related line is ignored by the mapper, so a line may contain:

::comment

The maximum length of map_from is 16 characters, the maximum length of map_to is 128 characters. Each entry takes exactly one line in the file. A nul character in either map_from or map_to is currently not supported.

Control characters may be written using the same escape sequences as permitted with TERMCAP.

The builtin map command may be used to enter additional maps at runtime.

As the nul character is the quote character of the mapper, enter two nul characters to get one nul character in the edit input. To enter a mapped string (such as cursor key output), first enter the quote character of the command line history editor (^), then enter nul character and finally the otherwise mapped text.

  Termcap

The termcap data base is used to make the command history editor independent from the terminal capabilities. Cursor key output is retrieved from the data base and mapped to the cursor movement commands of the history editor.

The following variables are used by termcap:

HOME
    To find the private files like $HOME/.termcap.

TERM
    A name representing the type of the current terminal.

TERMCAP
    This environment variable holds either a precompiled termcap entry or the pathname to be used to find a termcap database file. If it holds a precompiled entry that does not match the TERM environment, the termcap database is parsed as if the TERMCAP environment is not set. See section Parameter Substitution above for more information.

TERMPATH
    If TERMCAP is empty or not set, then the TERMPATH environment is scanned for pathnames of files that contain a termcap database. It holds a list of filenames separated by colons or spaces (i.e., ":" or " "). See section Parameter Substitution above for more information.

The following escape sequences are understood by the termcap implementation used by sh:

\\  The literal character \.
\E  The ESC character (ASCII 033).
\e  The ESC character (ASCII 033).
\^  The literal character ^.
\:  The literal character :.
\,  The literal character ,.
\b  The BACKSPACE character (ASCII 010).
\f  The FORMFEED character (ASCII 014).
\l  The LINEFEED character (ASCII 012).
\n  The NEWLINE character (ASCII 012).
\r  The CR character (ASCII 015).
\s  The SPACE character (ASCII 040).
\t  The TAB character (ASCII 007).
\v  The VERTICAL TAB character (ASCII 013).
^c  Maps to control(c) for any appropriate c.
^?  The DEL character (ASCII 0177).
\nnn
    Maps to a character with the octal representation nnn with 1..3 octal digits.
\0  Maps to ASCII 0200.
^@  Maps to ASCII 00.

Mapping \0 to ASCII 0200 is required by the termcap documentation. A real nul character created from (^@) is currently neither supported by the upper layers of termcap, nor by the upper layers of the mapper.

  Large File Behavior

The Bourne Shell is large file aware. See largefile(5) for an extended description of the behavior of sh and jsh when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

EXIT STATUS

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 execution of the shell file is abandoned. Otherwise, the shell returns the exit status of the last command executed (see also the exit command above).

  jsh Only

If the shell is invoked as jsh and an attempt is made to exit the shell while there are stopped jobs, the shell issues one warning:

There are stopped jobs.

This is the only message. If another exit attempt is made, and there are still stopped jobs they are sent a SIGHUP signal from the kernel and the shell is exited.

FILES
/etc/profile
    The system initialization file, executed for login shells.
/etc/sh.shrc
    The system wide startup file, executed for interactive shells.
$HOME/.profile
    The personal initialization file, executed for login shells after /etc/profile.
$HOME/.shrc
    The personal initialization file, executed after /etc/sh.shrc, for interactive shells when ENV is not set.
/etc/termcap
    The system wide TERMCAP file.
$HOME/.termcap
    The personal TERMCAP file.
$HOME/.bshmap
    A file with hand-crafted cursor mappings for the history editor.
$HOME/.history
    File with the saved the history after logout.
$HOME/.globals
    File with persistent global alias definitions.
.locals
    File with persistent directory local alias definitions.
/tmp/sh*
    Used as temporary files for here documents (<< redirection).
/dev/null
    NULL device used as stdin for non job-control background jobs.
/usr/lib/rsh
    The location of the restricted Bourne Shell binary.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

  /usr/bin/sh, /usr/bin/jsh

SEE ALSO

Intro(1), bc(1), echo(1), getoptcvt(1), kill(1), bsh(1), ved(1), ksh(1), ksh93(1), login(1), newgrp(1), pfsh(1), pfexec(1), ps(1), pwd(1), set(1), shell_builtins(1), stty(1), test(1), umask(1), wait(1), rsh(1M), su(1M), swap(1M), sysdef(1M), termcap(1), dup(2), exec(2), fork(2), pipe(2), ulimit(2), getrlimit(2), setrlimit(2), setlocale(3C), signal.h(3HEAD), passwd(4), profile(4), attributes(5), environ(5), largefile(5), XPG4(5)

WARNINGS

The use of setuid shell scripts is strongly discouraged.

NOTES

For compatibility with the Thompson shell, ^ is a synonym for | as pipeline separator. Do not use in new scripts.

Words used for filenames in input/output redirection are not interpreted for filename generation (see File Name Generation section above). For example, cat file1 >a* creates a file named a*.

Because commands in pipelines are run as separate processes, variables set in a pipeline have no effect on the parent shell.

If the input or the output of a while or until loop is redirected, the commands in the loop are run in a sub-shell, and variables set or changed there have no effect on the parent process:

   lastline=
   while read line
   do
           lastline=$line
   done < /etc/passwd
   echo "lastline=$lastline"       # lastline is empty!

In these cases, the input or output can be redirected by using exec, as in the following example:

   # Save standard input (file descriptor 0) as file
   # descriptor 3, and redirect standard input from the file
   /etc/passwd:
   exec 3<&0               # save standard input as fd 3
   exec </etc/passwd       # redirect input from file
   lastline=
   while read line
   do
           lastline=$line
   done
   exec 0<&3               # restore standard input
   exec 3<&-               # close file descriptor 3
   echo "$lastline"        # lastline

If you get the error message, "cannot fork, too many processes ", try using the wait(1) command to clean up your background processes. If this doesn't help, the system process table is probably full or you have too many active foreground processes. There is a limit to the number of process ids associated with your login, and to the number the system can keep track of.

Only the last process in a pipeline can be waited for.

If a command is executed, and a command with the same name is installed in a directory in the search path before the directory where the original command was found, the shell continues to exec the original command. Use the hash command to correct this situation.

The Bourne shell has a limitation on the effective UID for a process. If this UID is less than 100 (and not equal to the real UID of the process), then the UID is reset to the real UID of the process.

If not in job control mode, the shell implements both foreground and background jobs in the same process group and they all receive the same signals, which can lead to unexpected behavior. It is, therefore, recommended to switch on job control mode via set -m in an interactive environment.

There is only one namespace for both functions and parameters. A function definition will delete a parameter with the same name and vice-versa.

Parameter assignments that precede a special command affect the shell itself. Parameter assignments that precede the call of a function are ignored.

This version of the Bourne Shell fixed the order of evaluation for parameter assignements to be left to right instead of right to left (as implemented in previous versions). This may cause scripts to fail if they expect the old non-standard behavior.

When the shell executes a shell script that attempts to execute a non-existent command interpreter, the shell returns an erroneous diagnostic message that the shell script file does not exist.