sh(1)

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

SYNOPSIS

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

/usr/bin/bosh
 [-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 name bosh permits to call this implementaton even when /usr/bin/sh has been linked to another shell.

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). Job control may also be enabled by calling the shell via the standard name and then calling set -m or set -o monitor.

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. If the extended pipe syntax is enabled via set -o fdpipe, the pipe symbol (|) may be preceded by a digit that specifies the file descriptor which should be associated to the command from the left side instead of the default stdout, e.g. 2| for a pipe from stderr. 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. Each pipeline can be preceded by the reserved word !. This causes the exit status of the pipeline to become 0 if the exit status of the last command is non-zero, and 1 if the exit status of the last command is 0.

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.

select name [ in word ... ] do list done
The select command prints on standard error (file descriptor 2), the set of words, each preceded by a number. If in word ... is omitted, then the positional parameters are used instead. See Parameter Substitution. The PS3 prompt is printed and a line is read from the standard input. If this line consists of the number of one of the listed words, then the value of the variable name is set to the word corresponding to this number. If this line is empty. the selection list is printed again. Otherwise the value of the variable name is set to NULL. (See Blank Interpretation about NULL). The contents of the line read from standard input is saved in the shell variable REPLY. The list is executed for each selection until a break or EOF is encountered. If the REPLY variable is set to NULL by the execution of list, then the selection list is printed before displaying the PS3 prompt for the next selection.

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.

The optional opening parenthesis was not supported by older versions of sh.

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.

time pipeline
The pipeline is executed and the elapsed time as well as the user and system time are printed to standard error. The TIMEFORMAT variable can be set to a format string that specifies how the timing information should be displayed. Command based timing from set -o time is temporarily disabled while pipeline based timing is in effect. If time is followed by white space and a '-', it is interpreted as a normal command in order to permit time -p, as required by POSIX.

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    {   }
select     time

The reserved words !, select and time were not supported in older versions of sh.

  Comments Lines

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

  # commands

If the hash character # is the first character in a command line and hash commands have been enabled via set -o hashcmds, the whole line is processed by the hash command interpreter. This allows to have an alternate entry to the alias definitions that avoids complex quoting by working on the raw alias definitions.

Hash commands are frequently used to edit alias definitions using the command line history editor.

No I/O redirection is possible for hash commands. No exit code is created for hash commands, $? is left intact from the last regular command. Quoting is not possible for hash commands. For all hash commands, there is a built in help text that is printed when #c -help is called, where c is one of the command letters.

When hash commands are enabled, the character that immediately follows the # is the command character. The command character may be followed by one or more command modifier characters. The following commands are supported:

#a[g|l] name value
    Add a new all expand alias. Such an alias is expanded regardless where it occurs on the command line. Without modifier, the alias is entered into the current default table.

    The first word surrounded by spaces is taken as the alias name, after skipping spaces, all text up to the end of the line is taken as the alias value.

    When using the 'g' modifier, the command works on global aliases, regardless of the current default.

    When using the 'l' modifier, the command works on local aliases, regardless of the current default.

    At startup, the default is to use the global aliases.

#b[g|l] name value
    Add a new begin alias. Such an alias is only expanded for the first word in a command. Without modifier, the alias is entered into the current default table.

#d[g|l] name
    Removes the alias name from the list of known aliases. Without modifier, the alias is removed from the current default table.

#h
#?  Print an overview help for all # commands.

#l[g|l][h] [name]
    Lists aliases from the table. Without modifier, the aliases from the current default table are printed. Without name, all aliases are listed. With name, only matching aliases are listed. Wildcards may be used.

    When using the 'h' modifier, the alias is also entered into the command history. This permits to edit existing aliases with the history editor and to re-enter the modified entries into the list of aliases.

#p[g|l][a|b] name value
    With the #p command, an alias may be pushed on top of an existing alias without writing to the related file. When a pushed value is removed, the old definition reappears.

    When using the 'a' modifier, an all expand alias is pushed.

    When using the 'b' modifier, a begin alias is pushed.

#s[g|l]
    Set or list the default table for other # command alias operations. If no modifier letter is used, the current default is printed otherwise the new default is set.

#   When entered on the command line, this prints the shell version. When seen inside a shell script and a space follows, the rest of the line is interpreted as comment.

  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.

  Tilde Expansion

A tilde-prefix consists of an unquoted tilde character at the beginning of a word, followed by all of the characters preceding the first unquoted slash in the word, or all the characters in the word if there is no slash. In an assignment, multiple tilde-prefixes can be used: at the beginning of the word (that is, following the equal sign of the assignment), following any unquoted colon or both. A tilde-prefix in an assignment is terminated by the first unquoted colon or slash. If none of the characters in the tilde-prefix are quoted, the characters in the tilde-prefix following the tilde are treated as a possible login name from the user database.

A portable login name cannot contain characters outside the set given in the description of the LOGNAME environment variable. If the login name is null (that is, the tilde-prefix contains only the tilde), the tilde-prefix is replaced by the value of the variable HOME. If HOME is unset, the results are unspecified. Otherwise, the tilde-prefix is replaced by a pathname of the home directory associated with the login name obtained using the getpwnam function. If the system does not recognize the login name, the results are undefined.

Tilde expansion generally occurs only at the beginning of words, but an exception based on historical practice has been included:

PATH=/usr/xpg4/bin:~joerg/bin

is eligible for tilde expansion because tilde follows a colon and none of the relevant characters is quoted. Consideration was given to prohibiting this behavior because any of the following are reasonable substitutes:

PATH=$(printf %s ~karels/bin : ~bostic/bin)
for Dir in ~maart/bin ~srb/bin .
do
     PATH=${PATH:+$PATH:}$Dir
done

With the first command, explicit colons are used for each directory. In all cases, the shell performs tilde expansion on each directory because all are separate words to the shell.

Expressions in operands such as:

make -k mumble LIBDIR=~chet/lib

do not qualify as shell variable assignments and tilde expansion is not performed (unless the command does so itself, which make does not).

Because of the requirement that the word not be quoted, the following are not equivalent; only the last causes tilde expansion:

\~hlj/   ~h\lj/   ~"hlj"/   ~hlj\/   ~hlj/

The results of giving tilde with an unknown login name are undefined by POSIX because the Bourne Shell ~+ and ~- constructs make use of this condition, but in general it is an error to give an incorrect login name with tilde. The results of having HOME unset are unspecified because some historical shells treat this as an error.

If a tilde that matches the criteria is found, the word up to a / (or up to a : in case of a variable assignment) is checked to see if it matches a user name in the password database. If a match is found, the ~ and the matched login name are replaced by the login directory of the matched user. If no match is found, the original text is left unchanged. A ~ by itself, or in front of a /, is replaced by $HOME. A ~ followed by a + or - is replaced by the value of $PWD and $OLDPWD respectively.

  Command Substitution

The shell reads commands enclosed in parenthesis preceded by a dollar sign (that is, $(command) ) or 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 when using the second (obsolete) form using the backquoted syntax, where backslashes (\) are used to escape other characters.

When using the backquoted syntax, 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 in this form. 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.

In the $() form, nested command substitutions do not need special quoting.

Command substitution allows the output of a command to be substituted in place of the command name itself. Command substitution occurs when the command is enclosed as follows:

$(command)

or (backquoted version):

`command`

The shell expands the command substitution by executing command in a subshell environment and replacing the command substitution (the text of command plus the enclosing $() or backquotes) with the standard output of the command, removing sequences of one or more newline characters at the end of the substitution. Embedded newline characters before the end of the output is not be removed; however, they can be treated as field delimiters and eliminated during field splitting, depending on the value of IFS and quoting that is in effect.

With the $(command) form, all characters following the open parenthesis to the matching closing parenthesis constitute the command. Any valid shell script can be used for command.

The results of command substitution are not field splitting and pathname expansion processed for further tilde expansion, parameter expansion, command substitution or arithmetic expansion. If a command substitution occurs inside double-quotes, it is not be performed on the results of the substitution.

The $() form of command substitution solves a problem of inconsistent behavior when using backquotes. For example:

Additionally, the backquoted syntax has historical restrictions on the contents of the embedded command. While the new $() form can process any kind of valid embedded script, the backquoted form cannot handle some valid scripts that include backquotes. For example, these otherwise valid embedded scripts do not work in the left column, but do work on the right:

Because of these inconsistent behaviors, the backquoted variety of command substitution is not recommended for new applications that nest command substitutions or attempt to embed complex scripts.

If the command substitution consists of a single subshell, such as:

$( (command) )

a portable application must separate the $( and ( into two tokens (that is, separate them with white space). This is required to avoid any ambiguities with arithmetic expansion.

  Arithmetic Expansion

An arithmetic expression enclosed in double parentheses preceded by a dollar sign is replaced by the value of the arithmetic expression within the double parenthesis. Arithmetic expansion provides a mechanism for evaluating an arithmetic expression and substituting its value. The format for arithmetic expansion is as follows:

$((arithmetic-expression))

The expression is treated as if it were in double-quotes, except that a double-quote inside the expression is not treated specially. The shell expands all tokens in the expression for parameter expansion, command substitution and quote removal.

Next, the shell treats this as an arithmetic expression and substitutes the value of the expression. The arithmetic expression is processed according to the rules of the ISO C with the following exceptions:

    o   Only signed long long integer arithmetic is supported.

    o   The sizeof() operator is not supported.

    o   Selection, iteration, and jump statements are not supported.

If the expression is invalid, the expansion fails and the shell writes a message to standard error indicating the failure.

POSIX does not require to support the prefix and postfix ++ and -- operators, so avoid them in portable shell scripts.

POSIX does not require to support more than signed long arithmetic, so avoid arithmetic that requires more in portable scripts.

In older versions of sh, arithmetic expansion was not supported.

A simple example using arithmetic expansion:

# repeat a command 100 times
x=100
while [ $x -gt 0 ]
do
     command
     x=$((x-1))
done

  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, or when the parameter name contains a dot (.). 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}
    Use Default Values. If parameter is unset, 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}
    Assign Default Values. If parameter is unset, 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}
    Indicate Error if Null or Unset. 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}
    Indicate Error if Null or Unset. If parameter is set, 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}
    Use Alternative Value. If parameter is set and is non-null, substitute word; otherwise substitute nothing.

${parameter+word}
    Use Alternative Value. If parameter is set, substitute word; otherwise substitute nothing.

If the colon (:) is omitted from the above expressions, the shell only checks whether parameter is set or not. The following table summarizes the effect of the <colon>:

In all cases shown with "assign", parameter is assigned that value, which also replaces the expression.

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`}

${#parameter}
    String Length. The length in characters of the value of parameter. If parameter is * or @, the results are unspecified.

The following four varieties of parameter expansion provide for substring processing. In each case, pattern matching notation, rather than regular expression notation, is used to evaluate the patterns. If parameter is * or @, the results are unspecified. Enclosing the full parameter expansion string in double-quotes does not cause the following four varieties of pattern characters to be quoted, whereas quoting characters within the braces has this effect.

${parameter%word}
    Remove Smallest Suffix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the smallest portion of the suffix matched by the pattern deleted. If word begins with a '%', the character needs to be quoted.

${parameter%%word}
    Remove Largest Suffix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the largest portion of the suffix matched by the pattern deleted.

${parameter#word}
    Remove Smallest Prefix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the smallest portion of the prefix matched by the pattern deleted. If word begins with a '#', the character needs to be quoted.

${parameter##word}
    Remove Largest Prefix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the largest portion of the prefix matched by the pattern deleted.

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 the first character in the IFS variable or by a space, in case IFS is unset. If IFS is set to a null string, its first character does not exist, so the parameter values are concatenated.
    In older versions of sh, IFS was not evaluated for "$*" and the separator was always a space character.

@   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. Only the low 8 bits of the exit code from the command are visible unless exit code masking is switched off by ``set -o fullexitcode''. The ability to see all 32 bits from the exit code requires a modern operating system with support for waitid(2) in addition. If the executable file could not be found, the returned value is 127. If the file exists but could not be executed, the returned value is 126. If a command's exit code modulo 256 is zero and ``set -o fullexitcode'' is not in effect, the returned value is 128 except when the operating system does not support waitid(2). If the command was killed by a signal, the returned value is 128 + the signal number.

$   The decimal process number of this shell. In a subshell, this still expands to the same value as that of the current invoked shell.

!   The process number of the last background command invoked.

.sh.code
    The numerical reason waitid(2) returned for the child status change. It matches the CLD_* definitions from signal.h. Note that the numbers are usually in the range 1..6 but this is not guaranteed. Use ${.sh.codename} for portability.

.sh.codename
    The reason waitid(2) returned for the child status change as text that is generated by stripping off CLD_ from the related definitions from signal.h. Possible values are:

    EXITED
        The program had a normal termination and the exit(2) code is in ${.sh.status}.

    KILLED
        The program was killed by a signal, the signal number is in ${.sh.status} the signal name is in ${.sh.termsig}.

    DUMPED
        The program was killed by a signal, similar to KILLED above, but the program in addition created a core dump.

    TRAPPED
        A traced child has trapped.

    STOPPED
        The program was stopped by a signal, the signal number is in ${.sh.status} the signal name is in ${.sh.termsig}.

    CONTINUED
        A stopped child was continued.

    NOEXEC
        An existing file could not be executed. This can happen when e.g. either the type of the file is not plain file or when the file does not have execute permission, or when the argument list is too long.

        This is not a result from waitid(2) but from execve(2).

    NOTFOUND
        A file was not found and thus could not be executed.

        This is not a result from waitid(2) but from execve(2).

    The child codes NOEXEC and NOTFOUND in ${.sh.codename} need shared memory (e.g. from vfork(2)) to allow a reliable reporting.

.sh.pid
    The process number of the process that caused the current waitid(2) status.

.sh.shell
    The name of the shell. This shell returns:

    sh (Schily Bourne Shell)

.sh.signame
    The name of the causing signal. If the status is related to a set of waitid(2) return values, this is CHLD or CLD, depending on the os. When a trap(1) command is executed, ${.sh.signame} holds the signal that caused the trap.

.sh.signo
    The signal number related to ${.sh.signame}.

.sh.status
    The decimal value returned by the last synchronously executed command. The value is unaltered and contains the full int from the exit(2) call in the child in case the shell is run on a modern os.

.sh.termsig
    The signal name related to the numerical ${.sh.status} value. The translation to signal names takes place regardless of whether the child was terminated by a signal or terminated normally.

.sh.version
    A string that identifies the version of this shell.

Note that trying to use the ${.sh.xxx} parameters on older shells will cause the older shells to exit with a bad substitution message unless the shell is an interactive shell.

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:.

BEEP
    If set to off, the history editor will not beep in case of an error. Use this to allow e.g. silent working in meetings.

    The variable BEEP was not supported in older versions of sh.

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.

    The variable ENV was not supported in older versions of sh.

    The recommended content of the file ${ENV} is:

    set -o globalaliases
    set -o localaliases
    set -o fdpipe
    set -o hashcmds
    set -o hostprompt
    set -o time

    Make sure set -o time is the last entry to avoid timing the commands from the .shrc file.

FCEDIT
    The name default editor name for the fc command.

    The variable FCEDIT was not supported in older versions of sh, it is an artefact from ksh and required by a POSIX feature named user portability.

HISTFILE
    The name of the file to use in order to read or save the command history. If HISTFILE is not set before the shell reads the initial history at startup, the name $HOME/.history is used. HISTFILE is only supported if sh was compiled with support for history editing.

    The variable HISTFILE was not supported in older versions of sh.

HISTORY
    The maximum number of lines to keep in the command history editor. The default is to keep 128 lines of command history. HISTORY is only supported if sh was compiled with support for history editing. This is the historic name that is in use since 1984, it is used as a fallback, when the POSIX variable HISTSIZE (introduced 1992) was not set.

    The variable HISTORY was not supported in older versions of sh.

HISTSIZE
    The maximum number of lines to keep in the command history editor. The default is to keep 128 lines of command history. HISTSIZE is only supported if sh was compiled with support for history editing. This is the POSIX variable name that has precedence over HISTORY.

    The variable HISTSIZE was not supported in older versions of sh.

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 command exit must be used instead. The default is not to ignore EOF. See also the command set -o ignoreeof below. IGNOREEOF is only supported if sh was compiled with support for history editing.

    The variable IGNOREEOF was not supported in older versions of sh.

LINENO
    The line number of the current line within the script. This variable currently does not have all POSIX features.

    The variable LINENO was not supported in older versions of sh.

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.

    The variable OLDPWD was not supported in older versions of sh.

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.

PPID
    The process number of the parent of the shell. The variable is setup once at program start and then set readonly.

    The variable PPID was not supported in older versions of sh.

PS1 Primary prompt string, by default "$ " for normal users and " privileged users. Each time an interactive shell is ready to read a command, the value of this variable is subject to parameter expansion and written to standard error. See the description for set -o promptcmdsubst below for more information.

    The variable PS1 was not subject to parameter expansion in older versions of sh.

PS2 Secondary prompt string, by default "> ". Each time, the user enters a <newline> prior to completing a command line in an interactive shell, the value of this variable is subject to parameter expansion and written to standard error. See the description for set -o promptcmdsubst below for more information.

    The variable PS2 was not subject to parameter expansion in older versions of sh.

PS3 Selection prompt string, by default "#? ".

    The variable PS3 was not supported in older versions of sh.

PS4 Execution trace prompt string, by default "+ ". If unset, "+ " is used. The value of this variable is subject to parameter expansion and written to standard error. See the description for set -o promptcmdsubst below for more information.

    The variable PS4 was not supported in older versions of sh.

PWD The present working directory, set by the cd, the pushd and the popd command. POSIX requires PWD to be set and verified at program startup. This may prevent a login for users with a networked home directory in case of a NFS based hang.

    The variable PWD was not supported in older versions of sh.

REPLY
    This variable is set by the select statement and by the read special builtin command when no arguments are supplied.

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.

    The variable SAVEHISTORY was not supported in older versions of sh.

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. If the past pathname component equals to rsh or rbosh, the shell is swichted into a restricted shell.

SYSV3
    When the SYSV3 Environment is set, the builtin echo command is switched into SYSV3 mode and supports escape sequences and the BSD -n option to suppress the newline character at the end of the output.

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.

    The variable TERM was not supported in older versions of sh.

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.

    The variable TERMCAP was not supported in older versions of sh.

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.

    The variable TERMPATH was not supported in older versions of sh.

TIMEFORMAT
    Controls the output format for command timing. The % character introduces a format sequence that is expanded to a time value or other information.

    The meaning of format sequences are as follows:

    %%  Prints a literal %.

    %pT Set the threshold to p seconds, p is a single digit. If the number of seconds computed from adding the user and system cpu time is less than the threshold, the rest of the format string is not processed, except when the timing is a result of using the time reserved word; if this format appears at the beginning of TIMEFORMAT, the whole output is suppressed.

    %P  Prints the cpu percentage computed as 100*(U + S) / R. On multi-cpu systems, this value may be larger than 100.

    %[p][f]E
        Prints the elapsed (real) wallclock time in seconds.

    %[p][f]S
        Prints the number of cpu seconds spend in system mode.

    %[p][f]U
        Prints the number of cpu seconds spend in user mode.

    %W  Number of times the process was swapped.

    %X  The average amount in shared text space used in Kbytes. This field is currently not supported.

    %D  The average amount in unshared data space used in Kbytes. This field is currently not supported.

    %K  The average amount of unshared stack space used in Kbytes. This field is currently not supported.

    %M  The maximum memory the process had in use at any time in Kbytes. This field is currently not supported.

    %F  The number of major page faults (page faults that caused physical I/O).

    %R  The number of minor page faults (page faults that did not caused physical I/O).

    %I  The number of input operations

    %O  The number of output operations.

    %r  The number of socket messages received.

    %s  The number of socket messages sent.

    %k  The number of signals received.

    %w  Number of voluntary context switches (waits).

    %c  Number of involuntary context switches.

    %J  The name of this job. This string is only available when in job control mode.

    On some minimal POSIX systems and on BeOS and Haiku only the times are supported.

    The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point to be printed. A value larger than 6 is treated as 6. If p is not specified, the value 3 is used.

    The optional f is a letter specifying the format to be used. If it is missing, a plain floating point number based on seconds is used. The following characters are supported to specify a different format:

    l   The l-format is the POSIX output format for times(1). It always prints minutes and seconds in the following form: ddmdd.ppps.

    L   The L-format is similar to the l-format but it prints hours and minutes where the l-format prints just minutes regardless of whether there are more than 59 minutes. Minutes and hours are only printed if the value is more than 59 seconds or 59 minutes. The format is: ddhddmdd.ppps.

    :   The :-format is similar to the L-format but it prints no s after the seconds and it replaces m and h by :. The format is: dd:dd:dd.ppp.

    The value of the decimal point in the floating point formats above is subject to locale specific adoptions based on LC_NUMERIC or LC_ALL.

    If TIMEFORMAT is unset, the value:

    '%:E real %U user %S sys %P%% cpu'

    is used for automatic timing with set -o time and:

    '\nreal %6:E\nuser %6U\nsys %6S'

    is used for pipelines prefixed with the time reserved word. If TIMEFORMAT is empty, no timing information is printed. A recommended format that is similar to what csh(1) prints by default, but with the available precision from modern operating systems is:

    '%6:Er %6Uu %6Ss %P%% %I+%Oio %Fpf+%Ww'

    A trailing newline is added when the format string is displayed.

    The variable TIMEFORMAT was not supported in older versions of sh.

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

The shell gives default values to ENV, PATH, PS1, PS2, PS3, PS4, MAILCHECK, HISTORY, OPTIND, and IFS. Default values for HOME and MAIL are set by login(1). For security reasons, the value for IFS is never imported from the environment.

When the shell is initially in POSIX mode, it marks all variables imported from the environment with the export property. See Environment section below.

  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. If the file exists, and the noclobber option is on, this causes an error. Otherwise, it is truncated to zero length.

>|word
    Same as >, except that it overrides the noclobber option. This feature was not supported in older versions of sh.

>>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.

When the shell starts in POSIX mode, all variables imported from the environment are given the export property and the shell internal values cannot be modified independently from the values propagated via the environment to child processes.

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).

  Built-in Commands

The following commands are executed in the shell process. Input/output redirection is permitted for these commands. File descriptor 1 is the default output location. When Job Control is enabled, additional Built-in Commands are added to the shell's environment (see Job Control section below).

Commands marked with a + are treated specially in the following ways:

    1.  Parameter assignments that precede a special builtin command affect the shell itself.

    2.  I/O redirections are processed after variable assignments for variables that precede the builtin command.

    3.  Errors may cause a script that contains them to abort.

In older versions of sh, parameter assignments that precede any builtin command did affect the shell itself.

+ :

    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 using the alias shell built-in must be written with appropriate quoting so that it is suitable for reinput to the shell parser.

    The # commands provide an alternate interface to define aliases that does not use the standard shell parser. It thus does not require quoting that goes beyond the quoting needed for the final command line in the expanded command.

    The alias command was not supported in older versions of sh.

    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.

    -R
    -raw
    --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 can be edited in the raw format using # commands, see the related section above.

    Aliases are often used together with the dosh builtin in order to run small parameterized pseudo shell scripts. An alias to list files in the long format and to pipe the result into more(1) could be implemented this way:

        alias lm='dosh '\''ls -l "$@" | more'\'' lm-alias'

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.)

builtin [ -dis ] [ -f lib ] [ name ... ]

    The builtin command allows to manage builtin commands.

    When no name parameter and neither -d nor -f are specified, the list of builtin commands is printed. When -i is specified, only shell intrinsic commands are listed. When -s is specified, only special builtin commands are listed.

    When -d is specified, each named builtin command is deleted. Special builtin commands cannot be deleted.

    On platforms that allow to load dynamic libraries, -f allows to load a dynamic library that contains builtin commands.

    Without -d all name parameters are added as builtins.

    The builtin command was not supported in older versions of sh.

+ break [ n ]

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

cd [ -L | -P ] [ argument ]

    Change the current directory to argument. If arg is - the directory is changed to the previous directory. 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.

    -L  Handles the operation dot-dot (..) logically. Symbolic link components are not resolved before dot-dot components are processed and dot-dot (..) operations are handled by removing the path component to the left of the dot-dot (..) in the supplied path or in PWD.

    -P  Handles the operation dot-dot physically. Symbolic link components are resolved before dot-dot components are processed.

    If both -L and -P are specified, the last one applies. If neither -L nor -P is specified, cd behaves as if -P had been specified, except when in POSIX mode where the default is -L. See section COMPATIBILITY below.

    The options -L and -P and the special parameter - were not recognised by older versions of sh.

chdir [ -L | -P ] [ 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.

command [ -p ] [ -v | -V ] name [arg ...]

    Without the option -v or -V, command executes name with the arguments specified by arg.

    With -v or -V, name is not executed but a description of name is printed. With -V, the output is like the output from the type built-in command but function definitions are not listed. With -v, the output is less verbose.

    The option -p causes a default path to be searched that grants all POSIX commands to be found, rather than using the search path defined by the value of PATH.

    Functions are not searched when trying to execute name. In addition, if name refers to a special built-in, none of the special properties associated with the built-in commands marked with leading daggers are honored. For example, using command exec instead of exec prevents a script from terminating when an invalid redirection is specified.

    The command built-in command was not supported in older versions of sh.

+ 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 [ -L | -P ]

    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.

    -L  If the PWD shell parameter contains an absolute pathname of the current directory that does not contain the filenames dot or dot-dot, pwd writes this pathname to standard output, regardless of whether it contains filename components that refer to symbolic links. Otherwise, the -L option behaves like the -P option.

    -P  The absolute pathname written does not contain filename components that refer to files of type symbolic link.

    If both -L and -P are specified, the last one applies. If neither -L nor -P is specified, pwd behaves as if -P had been specified, except when in POSIX mode where the default is -L. See section COMPATIBILITY below.

    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 in order to implement parameterized 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.

errstr [ errno ]

    Print the error message for errno on stdout.

    The errstr command was not supported in older versions of sh.

+ eval [ argument ... ]

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

+ exec [-a name] [ 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. The -a option causes name rather than the first arg, to become argv[0] for the new process.

+ 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 [ -p ] [ name[=value] ... ]

    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. The -p option causes the word export to be inserted before each name. (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.

    The option -p was not supported in older versions of sh.
    Specifying a value was not supported in older versions of sh.

false

    The false builtin does nothing. A non-zero exit code (1) is returned. Used with until for infinite loops.

    The false command was not a builtin command in older versions of sh.
fc [-r] [-e editor] [first [last]]
fc -l [-nr] [first [last]]
fc -s [old=new] [first]

    The fc builtin lists, or edits and re-executes, commands previously entered to an interactive sh.

    In the first form, a range of commands from first to last is selected and edited followed by a re-execution of the edit result. If the editor returns a non-zero exit status, the commands are not re-executed.

    In the second form, a range of commands from first to last is listed.

    In the third form, the command specified by first is re-executed.

    When commands are edited or re-executed, the resulting lines are entered at the end of the history list and then re-executed by sh. The fc command that caused the editing or re-execution is not entered into the history list.

    The following options are supported:

    -e editor
        Use editor to edit the commands. The value in the FCEDIT variable is used as a default when -e is not specified. If FCEDIT is null or unset, ed is used as the editor.

    -l  List the commands rather than invoking an editor on them. The commands are written in the sequence indicated by the first and last operands and affected by -r, with each command preceded by the command number.

        In this case, the fc command is entered into the history.

    -n  Suppress command numbers when listing with -l.

    -r  Reverse the order of the commands listed or edited.

    -s  Re-execute the command without invoking an editor.

    The following operands are supported:

    first, last
        Select the commands to list or edit. The number of previous commands that can be accessed is determined by the value of the HISTSIZE variable. The value of first or last or both may be one of the following:

        [+]number
            A positive number representing a command number. Command numbers can be displayed with the -l option.

        -number
            A negative number representing the command that was executed number of commands previously. For example, -1 is the previous command.

        string
            A string indicating the most recently entered command that begins with that string. If the old=new operand is not also specified with -s, the string form of the first operand cannot contain an embedded equal-sign.

        If first is omitted, -15 is assumed in list mode (-l) and -1 in other cases. If 0 is used as the value for first, the whole history is selected.

    old=new
        Replace the first occurrence of the string old in the commands to be re-executed by the string new.

    Note that the history is an interactive feature; commands read from scripts are not entered into the history.

    The fc command was not supported in older versions of sh, it is an artefact from ksh from a time when ksh still needed an external editor to modify the history. The implementation that is used in this version of the Bourne Shell already supported fully integrated editing features in the command line in 1984 and uses concepts from 1982 that make fc a deprecated feature for editing commands in the history. fc is required by a POSIX feature named user portability, it should be avoided in favor of the history command.

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 character 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.

    If optstring starts with "() ", getopts supports long options with a single dash. Long options with a single dash have been introduced with Multics and appeared on UNIX around 1980, see e.g. kill(1).

    If a long name argument follows a single dash and cannot be identified as a long option, it is retried as a combination of single character letters. To suppress error messages, the optional initial colon in optstring must precede the "() ":

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

    In the above example, -file, --file, -input-file, --input-file are the equivalent of -f, and -output-file and --output-file is the equivalent of -o. Error messages from getopts are suppressed and a colon is placed in name when an option argument for an option like -f is missing.

    getopts also supports one or more long options with no related short option. You must set up a decimal numerical value >= 256 between two question mark signs in place of an option letter in optstring:

      getopts "f:(file)(input-file)?900?:(output-file)"

    In the above example, the long option --output-file is associated to the integer value 900 and in case the option --output-file was specified, string 900 is set up as the value for name.

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 [-nr] [first [last]]

    Print the current command history. The history command is only supported if sh was compiled with support for history editing.

    If no command or command range is specified, the last 16 commands are listed. If only first with a value of 0 is specified, the whole history is printed.

    The following options are supported:

    -n  Suppress command numbers when listing with -l.

    -r  Reverse the order of the commands listed or edited.

    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 | -s sig ] [ pid ] [ %job ] ...
kill -l [ sig ] ...

    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. The optional sig argument list may contain signal numbers or $? exit values that refer to a program terminated by a signal. (See kill(1)).

    The kill option -s and kill -l with arguments was not supported in older versions of sh.

killpg [ -sig | -s sig ] [ pgrp ] [ %job ] ...
killpg -l [ sig ] ...

    Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processgroups. See kill for more information.

    The killpg command was not supported in older versions of sh.

local [ name[=value] ... ]

    The given names are marked for local scope to the function from where local is called. The scope is effective for the rest of the function and its children or until local is called again with the same variable name. The local variable is created with the same content and attributes as the current variable. If the local variable is exported, it's local value is seen by child processes called from a function. If no arguments are given, variable names that have been marked for local scope are listed. It is an error to use local when not within a function.

    The local command was not supported in older versions of sh.

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.

pgrp [%jobid ...]

    Print the process groups and session groups for the specified processes or jobs. 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. If %jobid is omitted, the process group for the current shell and the process group for the tty connected to stdin of the pgrp command is printed.

    If the process group id equals the process id, the process ia a progrss group leader. If the session group id equals the process id, the process ia a session group leader.

    The pgrp command was not supported in older versions of sh.

popd [ -L | -P ] [ -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, then removes the directory stack element named by offset from the current directory stack and then makes it the new top directory stack element and performs a cd to this directory. The new directory name is always printed as it was not given as an argument. See dirs for an explanation of offset.

    -L  Handles the operation logically. Symbolic link components are not resolved before the PWD shell parameter is assigned the new value.

    -P  Handles the operation physically. Symbolic link components are resolved before the PWD shell parameter is assigned the new value.

    If both -L and -P are specified, the last one applies. If neither -L nor -P is specified, cd behaves as if -P had been specified, except when in POSIX mode where the default is -L. See section COMPATIBILITY below.

    The popd command was not supported in older versions of sh.

printf format [argument ...]

    The printf command writes formatted operands to the standard output. The argument operands are formatted under control of the format operand. The format operand is treated like a printf(3) format string and the escape sequences '\a', '\b', '\f', '\n', '\r', '\t', '\v', '\\' and '\ddd', where ddd is one to three octal digits, are expanded as if they were in a C string.

    In addition to the format specifiers %c, %s, %d, %i, %o, %u, %x, %X, the format %b is supported. The integers are handled internally as intmax_t to avoid range problems even though only the standard int type specifiers are supported in the format operand. The format %b is treated like %s except that escape sequences in the argument string are expanded as with the echo command.

    Field width and precision may be specified either numerically in the format operand or via the '*' format specifier and related arguments.

    The printf(3) flag characters '+', ' ', '#' and '0' are supported.

    The format operand is reused as often as necessary to satisfy the argument operands. If the format operand contains more format specifiers than argument operands have been specified, string formats are treated as if an empty string has been supplied and integer arguments are treated as if a 0 has been supplied.

    The printf command was not a builtin command in older versions of sh.

pushd [ -L | -P ] [ name ]
pushd [ -L | -P ] [ -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.

    -L  Handles the operation dot-dot (..) logically. Symbolic link components are not resolved before dot-dot components are processed and dot-dot (..) operations are handled by removing the path component to the left of the dot-dot (..) in the supplied path or in PWD.

    -P  Handles the operation dot-dot physically. Symbolic link components are resolved before dot-dot components are processed.

    If both -L and -P are specified, the last one applies. If neither -L nor -P is specified, pushd behaves as if -P had been specified, except when in POSIX mode where the default is -L. See section COMPATIBILITY below.

    The pushd command was not supported in older versions of sh.

pwd [ -L | -P ]

    Print the current working directory as absolute pathname that does not contain the filenames dot (.) or dot-dot (..). See pwd(1) for usage and description. The current working directory is kept in the shell parameter PWD.

    -L  If the PWD shell parameter contains an absolute pathname of the current directory that does not contain the filenames dot or dot-dot, pwd writes this pathname to standard output, regardless of whether it contains filename components that refer to symbolic links. Otherwise, the -L option behaves like the -P option.

    -P  The absolute pathname written does not contain filename components that refer to files of type symbolic link.

    If both -L and -P are specified, the last one applies. If neither -L nor -P is specified, pwd behaves as if -P had been specified, except when in POSIX mode where the default is -L. See section COMPATIBILITY below.

    The options -L and -P - were not recognised by older versions of sh.

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. If name is omitted then REPLY is used as the default name. The exit 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.

    Omiting the name parameter of the read command was not supported in older versions of sh.

+ readonly [ -p ] [ name[=value] ... ]

    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. The -p option causes the word readonly to be inserted before each name.

    The option -p was not supported in older versions of sh.
    Specifying a value was not supported in older versions of sh.

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 [ -abCefhkmntuvxP [ -o [ option ]] [ argument ... ] ]

    The set commands supports the following options:

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

    -b  Prints job completion messages as soon as a background job changes state rather than waiting for the next prompt. This options is currently without effect. The option -b was not supported in older versions of sh.

    -C  Prevents redirection (>) from truncating existing files. Files that are created are opened with the O_EXCL mode. Requires >| to truncate a file when turned on. The option -C was not supported in older versions of sh.

    -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.
        bgnice
            All background jobs are run at a lower priority. This is the default in interactive mode.
        errexit
            Equivalent to -e.
        fdpipe
            Enables the extended pipe syntax that allows to have a pipe output file descriptor number in front of the pipe sign (|), e.g. 2| for a pipe from stderr. It is recommended to put `set -o fdpipe' into the file $HOME/.shrc to enable the extended pipe syntax for interactive shells by default. Scripts that like to use this feature, need to enable it.
        fullexitcode
            Do not mask the exit code with 0xFF when expanding $?. This gives access to the full 32 bits from the child's exit code via $? on all modern operating systems that support waitid(2).
        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.
        hashcmds
            Enable hash commands, see section # commands above.
        hostprompt
            Set the PS1 value to ``hostname uname> '' if it was not yet changed from the default value.
        ignoreeof
            The POSIX variant of telling the shell not to exit on EOF; the command exit must be used instead. The original method of the history editor introduced in 1984 is to set IGNOREEOF=on see section Parameter Substitution for more information. If the parameter IGNOREEOF=on was set and ignoreeof is off, EOF is still ignored.
        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.
        noclobber
            Equivalent to -C.
        noexec
            Equivalent to -n.
        noglob
            Equivalent to -f.
        notify
            Equivalent to -b.
        nounset
            Equivalent to -u.
        onecmd
            Equivalent to -t.
        pfsh
            Equivalent to -P.
        posix
            Set the behavior of the Bourne Shell to POSIX mode where its default differs from the POSIX standard.
            This currently disallows to use ``^'' as the pipe symbol, switches off support for test -t without a parameter and sets the default for directory operations to -L. If this option is enabled at startup, all shell variables from the imported environment are given the export property.
            POSIX mode is enabled by default if the executable path of the shell equals a compiled in value, e.g. /usr/xpg4/bin/sh.
        privileged
            Equivalent to -p.
        promptcmdsubst
            Apply command substitution and arithmetic substitution to the variables PS1, PS2 and PS4. By default, promptcmdsubst is switched off to avoid security problems caused by imported variables. If promptcmdsubst is switched on, the variables PS1, PS2 and PS4 are reset to their default values for security reasons. Note that POSIX only requires parameter substitution, but no command substitution or arithmetic substitution for PS1, PS2 and PS4.
        restricted
            Equivalent to -r.
        stdin
            Equivalent to -s.
        time
            Switch on automatic timing for commands. The variable TIMEFORMAT may be used to control the output format.
        verbose
            Equivalent to -v.
        ved Allow shell command line editing using the built in ved(1) 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.

        The option -o was not supported in older versions of sh.

    -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 -. If no arguments follow this delimiter, then the positional parameters are unset.

        Older versions of sh did not allow to unset the positional parameters with ``set --''.

    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 names and values of all variables are printed. When is POSIX mode (via set -o posix), only shell variables are printed; otherwise functions are listed amongst the shell variables.

+ 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.
    -C file
        True if file exists and is a contiguous file. The option -C was not supported in older versions of sh.
    -d file
        True if file exists and is a directory.
    -D file
        True if file exists and is a door. The option -D was not supported in older versions of sh.
    -e file
        True if file exists. The option -e was not supported in older versions of sh.
    -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.
    -G file
        True if file exists and its group matches the effective group id of this process. The option -G was not supported in older versions of sh.
    -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.
    -N file
        True if file exists and its modification time is greater than its access time . The option -N was not supported in older versions of sh.
    -o option
        True if the option named option is on.
    -o ?option
        True if the option named option is a valid option name. The option -o was not supported in older versions of sh.
    -O file
        True if file exists and its owner matches the effective user id of this process. The option -O was not supported in older versions of sh.
    -p file
        True if file exists and is a named pipe (FIFO).
    -P file
        True if file exists and is an event port. The option -P was not supported in older versions of sh.
    -r file
        True if file exists and is readable.
    -s file
        True if file exists and has a size greater then zero.
    -S file
        True if file exists and is a socket. The option -S was not supported in older versions of sh.
    -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. When is POSIX mode (via set -o posix), file-descriptor must always be specified.
    -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.

    file1 -ef file2
        True if file1 and file2 exists and refer to the same file. The option -ef was not supported in older versions of sh.
    file1 -nt file2
        True if file1 exists and file2 does not or file1 is newer than file2. The option -nt was not supported in older versions of sh.
    file1 -ot file2
        True if file2 exists and file1 does not or file1 is older than file2. The option -ot was not supported in older versions of sh.

    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.

    The algorithm for determining the precedence of the operators and the return value that is generated is based on the number of arguments presented to test. (However, when using the [...] form, the right-bracket final argument is not counted in this algorithm.)

    In the following list, $1, $2, $3 and $4 represent the arguments presented to test as a condition, condition1, or condition2.

        0 arguments:
            Exit false (1).

        1 argument:
            Exit true (0) if $1 is not null. Otherwise, exit false.

        2 arguments:

            o   If $1 is !, exit true if $2 is null, false if $2 is not null.

            o   If $1 is a unary primary, exit true if the unary test is true, false if the unary test is false.

            o   Otherwise, produce unspecified results.

        3 arguments:

            o   If $2 is a binary primary, perform the binary test of $1 and $3.

            o   If $1 is !, negate the two-argument test of $2 and $3.

            o   If $1 is ( and $3 is ), perform the unary test of $2.

            o   Otherwise, produce unspecified results.

        4 arguments:

            o   If $1 is !, negate the three-argument test of $2, $3, and $4.

            o   If $1 is ( and $4 is ), perform the two-argument test of $2 and $3.

            o   Otherwise, the results are unspecified.

    Scripts should be careful when dealing with user-supplied input that could be confused with primaries and operators. Unless the application writer knows all the cases that produce input to the script, invocations like test "$1" -a "$2" should be written as test "$1" && test "$2" to avoid problems if a user supplied value such as $1 is set to ! and $2 is set to the null string. That is, in cases where maximal portability is of concern, replace test expr1 -a expr2 with test expr1 && test expr2, and replace test expr1 -o expr2 with test expr1 || test expr2. But notice that, in test, -a has higher precedence than -o, while && and || have equal precedence in the shell.

    + times

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

        The first line lists the shell's user and system times, the second line lists the children's user and system times.

    + 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.

        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 or EXIT, 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.

        If argument is -, all trap(s) n are reset to their original values.

        The - argument was not supported in older versions of sh.

    true

        The true builtin does nothing. A zero exit code is returned. Used with while for infinite loops.

        The true command was not a builtin command in older versions of sh.

    type [ -F ] [ name ... ]

        For each name, indicate how it would be interpreted if used as a command name. If the option -F is specified with no arguments, all defined functions are listed. type displays information about each operand identifying the operand as a shell built-in, shell intrinsic, function, alias, hashed command, or keyword, and where applicable, may display the operand's path name. The meaning is as follows:

        shell built-in
            A normal command built into the shell. Some of these commands do not need to be built into the shell. A command usually is in this group because it was built into the shell for historical reasons or because it is an extension to the current POSIX standard.

        special shell built-in
            A command built into the shell that is subject to special treatment. This type of commands needs to be built into the shell in order to be able to have the desired result.

        shell intrinsic
            A command built into the shell. This type of commands needs to be built into the shell in order to be able to have the desired result.

        global alias
            A global alias that is expanded in any directory.

        local alias
            A local alias that is bound to the current directory and expanded in the current directory only.

        function
            A function defined in this shell.

        keyword
            A keyword in the syntax of this shell.

        command
            An external command identified by it's path name.

        hashed command
            An external command that was already subject to a path name search and hashing.

    ulimit [ [-HS] [-a | -McdefilLmnPqrRsStuv] ]
    ulimit [ [-HS] [resource-option] ] 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.

        -M  address space limit (in kbytes), usually -v alias
        -c  maximum core file size (in 512-byte blocks)
        -d  maximum size of data segment or heap (in kbytes)
        -e  maximum scheduling priority
        -f  maximum file size (in 512-byte blocks)
        -i  maximum number of pending signals
        -l  maximum size of locked memory (in kbytes)
        -L  maximum number of file locks
        -m  maximum resident set size (in kbytes)
        -n  maximum file descriptor plus 1
        -P  maximum number of pseudo ttys
        -q  maximum number of POSIX message queues
        -r  maximum realtime priority
        -R  maximum realtime quantum (in usec)
        -s  maximum size of stack segment (in kbytes)
        -S  maximum size of swap (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.

        The unalias command was not supported in older versions of sh.

        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 [ -f | -v ] [ name ... ]

        For each name, remove the corresponding variable or function value. Readonly variables cannot be unset. If the option -v is used, only variables will be unset. If the option -f is used, only functions will be unset.

        The options -f and -v have not been supported in older versions of sh.

    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 or after set -m was called, 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 | -s signal ] %jobid

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

killpg [ -signal | -s signal ] %jobid

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

pgrp [%jobid ...]

    Print process group id's for jobs.

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 was defined with a prototype implementation in 1982 and has unique characteristics compared to other implementations. The basic editing functions have been inspired by the behavior of the editor ved(1). The command history editor in the Bourne Shell is using the same code that was introduced in 1984 with bsh(1).

The history is implemented as limited ring buffer. The last recently used command line is always moved from it's previous position in the history list to the most recent entry. 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:

^A  Move the cursor to the beginning of the current command line.

^C  Interrupt command line reading and parsing. The current command line is discarded and the next prompt is displayed. This helps to escape from the parser when it is in an unknown state.

^D  Erase the character under the cursor and then move the cursor to the next character.

DEL Erase one character to the left of the cursor.

^E  Move the cursor to the end of the current command line.

^F  Move cursor one character to the right.

^H  Move cursor one character to the left.

    Warning: On terminals that offer a large backspace key for deleting characters, ^H does not work directly as it is mapped to DEL. Use the Cursor left key instead in such a case.

^N  Move cursor to the next history line. See below for history navigation.

^P  Move cursor to the previous history line. See below for history navigation.

^U  Erase the whole line.

^V  Literal next, the next typed character is inserted into the command line without special meaning.

^^  Get next character, convert it into a control character and insert it into the command line.

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- ^D
    Erase the word to the right starting with the character under the cursor.

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

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

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

The following commands are available to navigate within the history:

^N  Move cursor to the next history line. When the cursor has been on the last line of the history, move the cursor to the first line of the history.

^P  Move cursor to the previous history line. When the cursor has been on the first line of the history, move the cursor to the last line of the history.

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. 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. If this text is usually interpreted by the history editor, you first need to type the history editing quoting character ^^. To be sure that you are able to literarily enter some text, type ^^^@ (control up-arrow followed by Nul and the text).

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.

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

TERM is set, the mapper establishes mappings for the following termcap capabilities:

ku  Key cursor up, mapped to ^P.
    The previous command line from the history is displayed.

kd  Key cursor down, mapped to ^N.
    The next command line from the history is displayed.

kr  Key cursor forward (right), mapped to ^F.
    Move cursor one character to the right.

kl  Key cursor left, mapped to ^H.
    Move cursor one character to the left.

kh  Key cursor -> Home, mapped to ^A.
    The Cursor is moved to the beginning of the current command line.

@7  Key cursor -> End, mapped to ^E.
    The Cursor is moved to the end of the current command line.

kD  Key Delete Character, mapped to \177 (DEL).
    Erase one character to the left of the cursor.

kb  Key Backspace, mapped to \177 (DEL).
    Erase one character to the left of the cursor.

    Note that the Backspace Key is the larger key that is just above the Carriage Return Key. In former times, this key was called Delete and send the \177 (DEL) character. Since companies followed the design of the IBM PC keyboard layout, the related key usually sends \010. If you like to literarily enter a backspace into the command line, type ^^^@^H (control up-arrow followed by Nul followed by ^H).

After the mappings from the termcap entry for the current terminal type have been established, the shell tries to read the file $HOME/.bshmap to retrieve additional mappings.

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 control ^ (^^) octal 036, then enter a 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), privileges(5), ps(1), pwd(1), set(1), shell_builtins(1), stty(1), test(1), umask(1), wait(1), waitid(2), rsh(1M), su(1M), swap(1M), sysdef(1M), termcap(1), ved(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*.

The built-in command . file reads the whole file before any commands are executed. When a command substitution, a set of commands from eval, dosh, repeat, command, fc, jobs or trap are parsed, the whole set of command are read at once. alias and unalias commands in the file do not apply to any commands defined in the file or inside a set of commands executed with the named built-ins.

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

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 -r 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.

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

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.

COMPATIBILITY
This Bourne Shell started with the source state from OpenSolaris build 51 from October 2006. It was later changed to the equivalent state of build 144 from July 2010. The changes up to build 147 have not been applied because these later versions from Sun reduced the functionality.

Most changes fixed bugs or added functionality without changing the expected previous behavior.

The following incompatible changes have been introduced in order to follow the POSIX standard.

parameter assignment
    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.

parameter assignment preceding builtin commands
    With this version of the Bourne Shell, parameter assignment preceding builtin commands only affects the shell itself if this is related to a special builtin command. In previous versions, this affected the shell itself for any builtin command.

parameter import from the environment
    When the shell is on POSIX mode, it sets the export property on all shell variables imported from the environment. This makes all changes in these variables automatically visible to the next child process. The historic behavior is to pass the imported values to the childs environment but to use a separate storage location for the internal shell variable until the export builtin is explicitly called for a specific variable.

syntax errors in builtin commands
    With this version of the Bourne Shell, only special builtin commands may terminate the whole shell in case that shell is not an interactive shell. In previous versions, all builtin commands could terminate a non-ineractive shell if a utility syntax error or a fatal utility error was encountered.

    The most prominent result of this change is that the builtin cd command no longer terminates a shell script in case that the cd command did not work for whatever reason. So be careful and always check the exit code in shell scripts.

cd  POSIX introduced new options -L and -P and defaults to logical mode while the historic Burne Shell did implement a physical mode that operates on normalized directory names.

    In logical mode, the command argument ../* may refer to different files than calling cd .. followed by a command with the argument *. In logical and physical mode, the command argument * may refer to different files than calling cd somedir followed by a command with the argument ../*.

    While the latter problem is caused by the existence of a symlink in the new path, the first problem is caused by the behavior of cd -L. This is why the Bourne Shell, when not in POSIX mode (set -o posix not set), did not change it's default behavior and assumes cd -P when neither -L nor -P have been specified.

continue
    With SVr2 (1986), a parameter was introduced for continue. Unfortunately, at the same time a bug was introduced and a big number did not continue the outermost loop, but rather did break the outermost loop. This shell fixes this bug.

functions
    There is now a separate name space for functions and shell variables. This is not expected to cause problems.

getopts
    POSIX requires getopts to set OPTARG to the failing option character in case that optstring starts with a :. Previous versions of the shell did unset OPTARG in case of a failure. POSIX also requires the shell variable related to the name argument from getopts to be set to ``?'' when getopts returns a non-zero exit code. Previous versions of the shell did set name to the null string in this case.

kill
    The option parsing of the kill command was modified to be compatible to the POSIX standard. This is not expected to cause problems as the change only affects marginal cases with negative process id's that caused problems before as well.

read
    The field splitting required by the POSIX standard does not skip multiple non-space field separators but rather assigns empty values to variables in such a case. This is a significant change in the behavior, but the historic behavior is not useful for non-space field separators as this would not allow to e.g. read the password file via read(1).

pipes and words
    When in POSIX mode, the ``^'' character is not accepted as an alternate pipe ``|'' symbol. This results in different word delimiting rules, words that contain ``^'' do not need to be quoted.

set
    The output of the set command with no arguments was modified to include the quoting required by the POSIX standard. This is not expected to cause problems but the new output may be used as shell.

    When in full POSIX mode (via set -o posix), functions are not listed amongst shell variables. This is expected to cause problems as POSIX does not include a method to list shell functions.

    Calling ``set --'' now causes the positional parameters to be unset. Previous versions of the shell left the positional parameters untouched in this case. A portable method to clear the positional parameters is to call ``shift $#''.

test
    The behavior of the builtin test utility was changed by POSIX. POSIX requires test to select it's behavior from the number of arguments in case that the number of arguments is in the range from 0..4. This results e.g. in ``test -r'' to return a zero exit code because ``-r'' is a non-empty string, while previous versions of the shell did return an error because ``-r'' is an unary operator that misses an argument. Correctly written scripts do not suffer from this change.

    When not in POSIX mode (set -o posix not set), test still understands test -t without a parameter for compatibility with UNIX scripts.

times
    The output of the times command was modified to be compatible to the POSIX standard. This is not expected to cause problems.

trap
    The output of the trap command was modified to be compatible to the POSIX standard. Scripts that depend on the output of the trap command, when listing existing trap state, should be converted to be portable by checking whether the output starts with trap -- and then use a POSIX compliant parser.

The following other incompatible changes have been introduced:

pipes
    While in the original Bourne Shell none of the commands from a pipeline command was a child of the original shell, this version of the Bourne Shell tries to make all simple commands in a pipeline children from the original shell. In addition, if a builtin command is the rightmost command of a pipeline, it will now be run in the original shell. This permits commands like:

    echo foo | read var

    to set the variable var in the main shell.

I/O redirection on compound commands
    With the original Bourne Shell, I/O redirection on compound commands cause the compound commands to be run in a subshell and variable assignment inside such constructs not to affect the main shell. This version of the shell tries to avoid to run compound commands with I/O redirection in a subshell. Variable assignment thus works as expected.

    If the input or the output of a while or until loop was redirected in the original Bourne Shell, the commands in the loop have been run in a sub-shell, and variables set or changed there had 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 could 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

    This version of the shell works with both variants.

time
    The time token is now a reserved word. This permits to time pipelines as a whole but may cause problems when people assume that it is a command. When in doubt, call "time -p" instead as the fact that the next word is an option disables the time token to be recognized as a reserved word.

AUTHORS
The Bourne Shell was initially written by Stephen Richard Bourne at Bell Labs in 1976. The SVr4 release was written by various authors at AT&T in 1989. The Bourne Shell was later maintained by various people at AT&T and Sun Microsystems. Since 2006, the Bourne Shell is maintained by Joerg Schilling.

The history editor has been added to the Bourne Shell in 2006. It was designed and implemented as a prototype in 1982 by Joerg Schilling on UNOS, the first UNIX clone. The current version of the history editor is compatible to ved(1). It was written in August 1984 by Joerg Schilling and P. Teuchert for the shell bsh(1) and is maintained by Joerg Schilling since 1985.

SOURCE DOWNLOAD
The source code for the Bourne Shell is included in the schilytools project and may be retrieved from the schilytools project at Sourceforge at:

    http://sourceforge.net/projects/schilytools/

The download directory is:

    http://sourceforge.net/projects/schilytools/files/

Check for the schily-*.tar.bz2 archives.

Separate project informations for the Schily Bourne Shell project may be retrieved from:

    http://schilytools.sourceforge.net/bosh.html