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Name

Synopsis

/usr/xpg4/bin/sh [ +-abCefhikmnoprstuvx ] [ +-o option ] ... [ -c string ] [ arg... ]

/usr/bin/rksh [ +-abCefhikmnoprstuvx ] [ +-o option ] ... [ -c string ] [ arg... ]

Availability

/usr/bin/ksh

/usr/bin/rksh

/usr/xpg4/bin/sh

Description

Definitions

; & ( ) | < >    NEWLINE SPACE TAB

A blank is a TAB or a SPACE. An identifier is a sequence of letters, digits, or underscores starting with a letter or underscore. Identifiers are used as names for functions and variables. A word is a sequence of characters separated by one or more non-quoted metacharacters.

A command is a sequence of characters in the syntax of the shell language. The shell reads each command and carries out the desired action either directly or by invoking separate utilities. A special-command is a command that is carried out by the shell without creating a separate process. Except for documented side effects, most special commands can be implemented as separate utilities.

Commands

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

A list is a sequence of one or more pipelines separated by ;, &, &&, or ||, and optionally terminated by ;, &, or |&. Of these five 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; an ampersand (&) causes asynchronous execution of the preceding pipeline (that is, the shell does not wait for that pipeline to finish). The symbol |& causes asynchronous execution of the preceding command or pipeline with a two-way pipe established to the parent shell.

The standard input and output of the spawned command can be written to and read from by the parent shell using the -p option of the special commands read and print described in Special Commands. The symbol && (||) causes the list following it to be executed only if the preceding pipeline returns 0 (or a non-zero) value. An arbitrary number of new-lines may appear in a list, instead of a semicolon, to delimit a command.

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 identifier [ in word ... ] ; do list ; done

Each time a for command is executed, identifier 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 below). Execution ends when there are no more words in the list.

select identifier [ in word ... ] ; do list ; done

A select command prints to 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 below). 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 identifier 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 identifier 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 below).

if list ; then list ;

[ elif list ; then list ; ... ] [ else list ; ] fi

The list following if is executed and, if it returns an exit status of 0, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is 0, 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 0 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 0, executes the do list; otherwise the loop terminates. If no commands in the do list are executed, then the while command returns 0 exit status; until may be used in place of while to negate the loop termination test.

(list)

Execute list in a separate environment. Note, that if two adjacent open parentheses are needed for nesting, a space must be inserted to avoid arithmetic evaluation as described below.

{list}

list is simply executed. Note that unlike the metacharacters ( and ), { and } are reserved words and must occur at the beginning of a line or after a ; in order to be recognized.

[[expression]]

Evaluates expression and returns 0 exit status when expression is true. See Conditional Expressions below, for a description of expression.

function identifier { list ;}

identifier() { list ;}

Define a function which is referenced by identifier. The body of the function is the list of commands between { and }. (See Functions below).

time pipeline

The pipeline is executed and the elapsed time as well as the user and system time are printed to standard error.

The following reserved 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 { } function select time [[ ]]

Comments

Aliasing

Aliasing is performed when scripts are read, not while they are executed. Therefore, for an alias to take effect the alias definition command has to be executed before the command which references the alias is read.

Aliases are frequently used as a short hand for full path names. An option to the aliasing facility allows the value of the alias to be automatically set to the full pathname of the corresponding command. These aliases are called tracked aliases. The value of a tracked alias is defined the first time the corresponding command is looked up and becomes undefined each time the PATH variable is reset. These aliases remain tracked so that the next subsequent reference will redefine the value. Several tracked aliases are compiled into the shell. The -h option of the set command makes each referenced command name into a tracked alias.

The following exported aliases are compiled into (and built-in to) the shell but can be unset or redefined:

autoload=fmtypeset -fufm
false=fmlet 0fm
functions=fmtypeset -ffm
hash=fmalias -tfm
history=fmfc -lfm
integer=fmtypeset -ifm
nohup=fmnohup fm
r=fmfc -e -fm
true=fm:fm
type=fmwhence -vfm

An example concerning trailing blank characters and reserved words follows. If the user types:

$ alias foo="/bin/ls "

$ alias while="/"

The effect of executing:

$ while true

> do

> echo "Hello, World"

> done

is a never-ending sequence of Hello, World strings to the screen. However, if the user types:

$ foo while

the result will be an ls listing of /. Since the alias substitution for foo ends in a space character, the next word is checked for alias substitution. The next word, while, has also been aliased, so it is substituted as well. Since it is not in the proper position as a command word, it is not recognized as a reserved word.

If the user types:

$ foo; while

while retains its normal reserved-word properties.

Tilde Substitution

In addition, tilde substitution is attempted when the value of a variable assignment begins with a ~.

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 will be replaced by the value of the variable HOME . If HOME is unset, the results are unspecified. Otherwise, the tilde-prefix will be 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 =/posix/bin:~dgk/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.

Note that 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).

The special sequence $~ has been designated for future implementations to evaluate as a means of forcing tilde expansion in any word.

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

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

The results of giving tilde with an unknown login name are undefined because the KornShell ~+ 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.

Command Substitution

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 will expand 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 will not be removed; however, they may be treated as field delimiters and eliminated during field splitting, depending on the value of IFS and quoting that is in effect.

Within the backquoted style of command substitution, backslash shall retain its literal meaning, except when followed by:

$ ‘ \

(dollar-sign, backquote, backslash). The search for the matching backquote is satisfied by the first backquote found without a preceding backslash; during this search, if a non-escaped backquote is encountered within a shell comment, a here-document, an embedded command substitution of the $(command) form, or a quoted string, undefined results occur. A single- or double-quoted string that begins, but does not end, within the ‘...‘ sequence produces undefined results.

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, except:

• A script consisting solely of redirections produces unspecified results.
• See the restriction on single subshells described below.

The results of command substitution will not be 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 will not be performed on the results of the substitution.

Command substitution can be nested. To specify nesting within the backquoted version, the application must precede the inner backquotes with backslashes; for example:

‘\‘command\‘‘

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

Command	Output
echo ’\$x’	\$x
echo ‘echo ’\$x’‘	$x
echo $(echo ’\$x’)	\$x

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:

echo ‘	echo $(
cat <<eeof	cat <<eeof
a here-doc with ‘	a here-doc with )
eof	eof
‘	)
echo ‘	echo $(
echo abc # a comment with ‘	echo abc # a comment with )
‘	)
echo ‘	echo $(
echo ’‘’	echo ’)’
‘	)

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

$((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 will expand all tokens in the expression for parameter expansion, command substitution and quote removal.

Next, the shell will treat this as an arithmetic expression and substitute the value of the expression. The arithmetic expression will be processed according to the rules of the ISO C with the following exceptions:

• Only integer arithmetic is required.
• The sizeof() operator and the prefix and postfix ++ and -- operators are not required.
• Selection, iteration and jump statements are not supported.

As an extension, the shell may recognize arithmetic expressions beyond those listed. If the expression is invalid, the expansion will fail and the shell will write a message to standard error indicating the failure.

A simple example using arithmetic expansion:

# repeat a command 100 times

x=100

while [ $x -gt 0 ]

do

command

x=$(($x-1))

done

Process Substitution

paste <(cut -f1 file1) <(cut -f3 file2) | tee >( process1) >( process2)

cuts fields 1 and 3 from the files file1 and file2 respectively, pastes the results together, and sends it to the processes process1 and process2, as well as putting it onto the standard output. Note that the file, which is passed as an argument to the command, is a UNIX pipe(2) so programs that expect to lseek(2) on the file will not work.

Parameter Substitution

The shell supports a one-dimensional array facility. An element of an array variable is referenced by a subscript. A subscript is denoted by a [, followed by an arithmetic expression (see Arithmetic Evaluation below) followed by a ]. To assign values to an array, use set -A name value .... The value of all subscripts must be in the range of 0 through 1023. Arrays need not be declared. Any reference to a variable with a valid subscript is legal and an array will be created if necessary. Referencing an array without a subscript is equivalent to referencing the element 0. If an array identifier with subscript * or @ is used, then the value for each of the elements is substituted (separated by a field separator character).

The value of a variable may be assigned by writing:

name=value [ name=value ] ...

If the integer attribute, -i, is set for name, the value is subject to arithmetic evaluation as described below.

Positional parameters, parameters denoted by a number, may be assigned values with the set special command. Parameter $0 is set from argument zero when the shell is invoked. If parameter is one or more digits then it is a positional parameter. A positional parameter of more than one digit must be enclosed in braces.

Parameter Expansion

${expression}

where expression consists of all characters until the matching }. Any } escaped by a backslash or within a quoted string, and characters in embedded arithmetic expansions, command substitutions and variable expansions, are not examined in determining the matching }.

The simplest form for parameter expansion is:

${parameter}

The value, if any, of parameter will be substituted.

The parameter name or symbol can be enclosed in braces, which are optional except for positional parameters with more than one digit or when parameter is followed by a character that could be interpreted as part of the name. The matching closing brace will be determined by counting brace levels, skipping over enclosed quoted strings and command substitutions.

If the parameter name or symbol is not enclosed in braces, the expansion will use the longest valid name whether or not the symbol represented by that name exists. When the shell is scanning its input to determine the boundaries of a name, it is not bound by its knowledge of what names are already defined. For example, if F is a defined shell variable, the command:

echo $Fred

does not echo the value of $F followed by red; it selects the longest possible valid name, Fred, which in this case might be unset.

If a parameter expansion occurs inside double-quotes:

• Pathname expansion will not be performed on the results of the expansion.
• Field splitting will not be performed on the results of the expansion, with the exception of @.

In addition, a parameter expansion can be modified by using one of the following formats. In each case that a value of word is needed (based on the state of parameter, as described below), word will be subjected to tilde expansion, parameter expansion, command substitution and arithmetic expansion. If word is not needed, it will not be expanded. The } character that delimits the following parameter expansion modifications is determined as described previously in this section and in dquote. (For example, ${foo-bar}xyz} would result in the expansion of foo followed by the string xyz} if foo is set, else the string barxyz}).

${parameter:-word}

Use Default Values. If parameter is unset or null, the expansion of word will be substituted; otherwise, the value of parameter will be substituted.

${parameter:=word}

Assign Default Values. If parameter is unset or null, the expansion of word will be assigned to parameter. In all cases, the final value of parameter will be 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 unset or null, the expansion of word (or a message indicating it is unset if word is omitted) will be written to standard error and the shell will exit with a non-zero exit status. Otherwise, the value of parameter will be substituted. An interactive shell need not exit.

${parameter:+[word]}

Use Alternative Value. If parameter is unset or null, null will be substituted; otherwise, the expansion of word will be substituted.

In the parameter expansions shown previously, use of the colon in the format results in a test for a parameter that is unset or null; omission of the colon results in a test for a parameter that is only unset. The following table summarizes the effect of the colon:

	parameter	parameter	parameter
	set and not null	set but null	unset
${parameter:-word}	substitute	substitute	substitute
	parameter	word	word
${parameter-word}	substitute	substitute	substitute
	parameter	null	word
${parameter:=word}	substitute	assign	assign
	parameter	word	word
${parameter=word}	substitute	substitute	assign
	parameter	parameter	null
${parameter:?word}	substitute	error,	error,
	parameter	exit	exit
${parameter?word}	substitute	substitute	error,
	parameter	null	exit
${parameter:+word}	substitute	substitute	substitute
	word	null	null
${parameter+word}	substitute	substitute	substitute
	word	word	null

In all cases shown with ‘substitute’, the expression is replaced with the value shown. In all cases shown with ‘assign’ parameter is assigned that value, which also replaces the expression.

${#parameter}

String Length. The length in characters of the value of parameter. If parameter is * or @, then all the positional parameters, starting with $1, are substituted (separated by a field separator character).

The following four varieties of parameter expansion provide for substring processing. In each case, pattern matching notation (see patmat), rather than regular expression notation, will be used to evaluate the patterns. If parameter is * or @, then all the positional parameters, starting with $1, are substituted (separated by a field separator character). Enclosing the full parameter expansion string in double-quotes will not cause the following four varieties of pattern characters to be quoted, whereas quoting characters within the braces will have this effect.

${parameter%word}

Remove Smallest Suffix Pattern. The word will be expanded to produce a pattern. The parameter expansion then will result in parameter, with the smallest portion of the suffix matched by the pattern deleted.

${parameter%%word}

Remove Largest Suffix Pattern. The word will be expanded to produce a pattern. The parameter expansion then will result in parameter, with the largest portion of the suffix matched by the pattern deleted.

${parameter#word}

Remove Smallest Prefix Pattern. The word will be expanded to produce a pattern. The parameter expansion then will result in parameter, with the smallest portion of the prefix matched by the pattern deleted.

${parameter##word}

Remove Largest Prefix Pattern. The word will be expanded to produce a pattern. The parameter expansion then will result in parameter, with the largest portion of the prefix matched by the pattern deleted.

Examples:

${parameter:-word}

In this example, ls is executed only if x is null or unset. (The $(ls) command substitution notation is explained in Command Substitution above.)

${x:-$(ls)}

${parameter:=word}

unset X

echo ${X:=abc}

abc

${parameter:?word}

unset posix

echo ${posix:?}

sh: posix: parameter null or not set

${parameter:+word}

set a b c

echo ${3:+posix}

posix

${#parameter}

HOME=/usr/posix

echo ${#HOME}

10

${parameter%word}

x=file.c

echo ${x%.c}.o

file.o

${parameter%%word}

echo ${x%%/*}

posix

${parameter#word}

x=$HOME/src/cmd

echo ${x#$HOME}

/src/cmd

${parameter##word}

x=/one/two/three

echo ${x##*/}

three

Parameters Set by Shell

#

The number of positional parameters in decimal.

-

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

?

The decimal value returned by the last executed command.

$

The process number of this shell.

_

Initially, the value of _ is an absolute pathname of the shell or script being executed as passed in the environment. Subsequently it is assigned the last argument of the previous command. This parameter is not set for commands which are asynchronous. This parameter is also used to hold the name of the matching MAIL file when checking for mail.

!

The process number of the last background command invoked.

ERRNO

The value of errno as set by the most recently failed system call. This value is system dependent and is intended for debugging purposes.

LINENO

The line number of the current line within the script or function being executed.

OLDPWD

The previous working directory set by the cd command.

OPTARG

The value of the last option argument processed by the getopts special command.

OPTIND

The index of the last option argument processed by the getopts special command.

PPID

The process number of the parent of the shell.

PWD

The present working directory set by the cd command.

RANDOM

Each time this variable is referenced, a random integer, uniformly distributed between 0 and 32767, is generated. The sequence of random numbers can be initialized by assigning a numeric value to RANDOM.

REPLY

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

SECONDS

Each time this variable is referenced, the number of seconds since shell invocation is returned. If this variable is assigned a value, then the value returned upon reference will be the value that was assigned plus the number of seconds since the assignment.

Variables Used by Shell

CDPATH

The search path for the cd command.

COLUMNS

If this variable is set, the value is used to define the width of the edit window for the shell edit modes and for printing select lists.

EDITOR

If the value of this variable ends in emacs, gmacs, or vi and the VISUAL variable is not set, then the corresponding option (see the set special command below) will be turned on.

ENV

This variable, when the shell is invoked, is subjected to parameter expansion by the shell and the resulting value is used as a pathname of a file containing shell commands to execute in the current environment. The file need not be executable. If the expanded value of ENV is not an absolute pathname, the results are unspecified. ENV will be ignored if the user’s real and effective user IDs or real and effective group IDs are different.

This variable can be used to set aliases and other items local to the invocation of a shell. The file referred to by ENV differs from $HOME/.profile in that .profile is typically executed at session startup, whereas the ENV file is executed at the beginning of each shell invocation. The ENV value is interpreted in a manner similar to a dot script, in that the commands are executed in the current environment and the file needs to be readable, but not executable. However, unlike dot scripts, no PATH searching is performed. This is used as a guard against Trojan Horse security breaches.

FCEDIT

The default editor name for the fc command.

FPATH

The search path for function definitions. By default the FPATH directories are searched after the PATH variable. If an executable file is found, then it is read and executed in the current environment. FPATH is searched before PATH when a function with the -u attribute is referenced. The preset alias autoload preset alias causes a function with the -u attribute to be created.

IFS

Internal field separators, normally space, tab, and new-line that are used to separate command words which result from command or parameter substitution and for separating words with the special command read. The first character of the IFS variable is used to separate arguments for the $* substitution (See Quoting below).

HISTFILE

If this variable is set when the shell is invoked, then the value is the pathname of the file that will be used to store the command history. (See Command re-entry below.)

HISTSIZE

If this variable is set when the shell is invoked, then the number of previously entered commands that are accessible by this shell will be greater than or equal to this number. The default is 128.

HOME

The default argument (home directory) for the cd command.

LC_ALL

This variable provides a default value for the LC_* variables.

LC_COLLATE

This variable determines the behavior of range expressions, equivalence classes and multi-character collating elements within pattern matching.

LC_CTYPE

Determines how the shell handles characters. When LC_CTYPE is set to a valid value, the shell can display and handle text and filenames containing valid characters for that locale. However, the shell is not multibyte (EUC) capable. In the "C" locale, only ASCII characters are valid. If LC_CTYPE (see environ(5) ) is not set in the environment, the operational behavior of the shell is determined by the value of the LANG environment variable. If LC_ALL is set, its contents are used to override both the LANG and the other LC_* variables. If none of the above variables is set in the environment, the "C" (U.S. style) locale prevails.

LC_MESSAGES

This variable determines the language in which messages should be written.

LANG

Provide a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default "C" locale will be used. If any of the internationalization variables contains an invalid setting, the utility will behave as if none of the variables had been defined.

LINENO

This variable is set by the shell to a decimal number representing the current sequential line number (numbered starting with 1) within a script or function before it executes each command. If the user unsets or resets LINENO , the variable may lose its special meaning for the life of the shell. If the shell is not currently executing a script or function, the value of LINENO is unspecified.

LINES

If this variable is set, the value is used to determine the column length for printing select lists. Select lists will print vertically until about two-thirds of LINES lines are filled.

MAIL

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

MAILCHECK

This variable specifies how often (in seconds) the shell will check for changes in the modification time of any of the files specified by the MAILPATH or MAIL variables. The default value is 600 seconds. When the time has elapsed the shell will check before issuing the next prompt.

MAILPATH

A colon (:) separated list of file names. If this variable is set, then the shell informs the user of any modifications to the specified files that have occurred within the last MAILCHECK seconds. Each file name can be followed by a ? and a message that will be printed. The message will undergo parameter substitution with the variable $_ defined as the name of the file that has changed. The default message is you have mail in $_.

NLSPATH

Determine the location of message catalogues for the processing of LC_MESSAGES .

PATH

The search path for commands (see Execution below). The user may not change PATH if executing under rksh (except in .profile).

PPID

This variable is set by the shell to the decimal process ID of the process that invoked the shell. In a subshell, PPID will be set to the same value as that of the parent of the current shell. For example, echo $PPID and (echo $PPID) would produce the same value.

PS1

The value of this variable is expanded for parameter substitution to define the primary prompt string which by default is ‘‘$ ’’. The character ! in the primary prompt string is replaced by the command number (see Command Re-entry below). Two successive occurrences of ! will produce a single ! when the prompt string is printed.

PS2

Secondary prompt string, by default ‘‘> ’’.

PS3

Selection prompt string used within a select loop, by default ‘‘#? ’’.

PS4

The value of this variable is expanded for parameter substitution and precedes each line of an execution trace. If omitted, the execution trace prompt is ‘‘+ ’’.

SHELL

The pathname of the shell is kept in the environment. At invocation, if the basename of this variable is rsh, rksh, or krsh, then the shell becomes restricted.

TMOUT

If set to a value greater than zero, the shell will terminate if a command is not entered within the prescribed number of seconds after issuing the PS1 prompt. (Note that the shell can be compiled with a maximum bound for this value which cannot be exceeded.)

VISUAL

If the value of this variable ends in emacs, gmacs, or vi then the corresponding option (see Special Command set below) will be turned on.

The shell gives default values to PATH , PS1 , PS2 , PS3 , PS4 , MAILCHECK , FCEDIT , TMOUT and IFS , while HOME, SHELL ENV and MAIL are not set at all by the shell (although HOME is set by login(1) ). On some systems MAIL and SHELL are also set by login.

Blank Interpretation

File Name Generation

ls .@(r*)

would locate a file named .restore, but ls @(.r*) would not. In other instances of pattern matching the / and . are not treated specially.

*

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 "! ", then any character not enclosed is matched. A - can be included in the character set by putting it as the first or last character.

A pattern-list is a list of one or more patterns separated from each other with a |. Composite patterns can be formed with one or more of the following:

?(pattern-list)

Optionally matches any one of the given patterns.

*(pattern-list)

Matches zero or more occurrences of the given patterns.

+(pattern-list)

Matches one or more occurrences of the given patterns.

@(pattern-list)

Matches exactly one of the given patterns.

!(pattern-list)

Matches anything, except one of the given patterns.

Quoting

The special meaning of reserved words or aliases can be removed by quoting any character of the reserved word. The recognition of function names or special command names listed below cannot be altered by quoting them.

Arithmetic Evaluation

An arithmetic expression uses the same syntax, precedence, and associativity of expression as the C language. All the integral operators, other than ++, --, ?:, and , are supported. Variables can be referenced by name within an arithmetic expression without using the parameter substitution syntax. When a variable is referenced, its value is evaluated as an arithmetic expression.

An internal integer representation of a variable can be specified with the -i option of the typeset special command. Arithmetic evaluation is performed on the value of each assignment to a variable with the -i attribute. If you do not specify an arithmetic base, the first assignment to the variable determines the arithmetic base. This base is used when parameter substitution occurs.

Since many of the arithmetic operators require quoting, an alternative form of the let command is provided. For any command which begins with a ((, all the characters until a matching )) are treated as a quoted expression. More precisely, ((...)) is equivalent to let "...".

Prompting

Conditional Expressions

-a file

True, if file exists.

-b file

True, if file exists and is a block special file.

-c file

True, if file exists and is a character special file.

-d file

True, if file exists and is a directory.

-e file

True, if file exists.

-f file

True, if file exists and is an ordinary file.

-g file

True, if file exists and is has its setgid bit set.

-k file

True, if file exists and is has its sticky bit set.

-n string

True, if length of string is non-zero.

-o option

True, if option named option is on.

-p file

True, if file exists and is a fifo special file or a pipe.

-r file

True, if file exists and is readable by current process.

-s file

True, if file exists and has size greater than zero.

-t fildes

True, if file descriptor number fildes is open and associated with a terminal device.

-u file

True, if file exists and has its setuid bit set.

-w file

True, if file exists and is writable by current process.

-x file

True, if file exists and is executable by current process. If file exists and is a directory, then the current process has permission to search in the directory.

-z string

True, if length of string is zero.

-L file

True, if file exists and is a symbolic link.

-O file

True, if file exists and is owned by the effective user id of this process.

-G file

True, if file exists and its group matches the effective group id of this process.

-S file

True, if file exists and is a socket.

file1 -nt file2

True, if file1 exists and is newer than file2.

file1 -ot file2

True, if file1 exists and is older than file2.

file1 -ef file2

True, if file1 and file2 exist and refer to the same file.

string

True if the string string is not the null string.

string = pattern

True, if string matches pattern.

string != pattern

True, if string does not match pattern.

string1 = string2

True if the strings string1 and string2 are identical.

string1 ! = string2

True if the strings string1 and string2 are not identical.

string1 < string2

True, if string1 comes before string2 based on ASCII value of their characters.

string1 > string2

True, if string1 comes after string2 based on ASCII value of their characters.

exp1 -eq exp2

True, if exp1 is equal to exp2.

exp1 -ne exp2

True, if exp1 is not equal to exp2.

exp1 -lt exp2

True, if exp1 is less than exp2.

exp1 -gt exp2

True, if exp1 is greater than exp2.

exp1 -le exp2

True, if exp1 is less than or equal to exp2.

exp1 -ge exp2

True, if exp1 is greater than or equal to exp2.

In each of the above expressions, if file is of the form /dev/fd/n, where n is an integer, then the test is applied to the open file whose descriptor number is n.

A compound expression can be constructed from these primitives by using any of the following, listed in decreasing order of precedence.

(expression)

True, if expression is true. Used to group expressions.

! expression

True if expression is false.

expression1 && expression2

True, if expression1 and expression2 are both true.

expression1 || expression2

True, if either expression1 or expression2 is true.

Input/Output

<word

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

>word

Use file word as standard output (file descriptor 1). If the file does not exist then it is created. If the file exists, and the noclobber option is on, this causes an error; otherwise, it is truncated to zero length.

>|word

Sames as >, except that it overrides the noclobber option.

>>word

Use file word as standard output. If the file exists then 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

The shell input is read up to a line that is the same as word, or to an EOF . No parameter substitution, command substitution or file name generation is performed on word. The resulting document, called a here-document, becomes the standard input. If any character of word is quoted, then no interpretation is placed upon the characters of the document; otherwise, parameter and command substitution occur, \NEWLINE is ignored, and \ must be used to quote the characters \, $, ‘, and the first character of word. If - is appended to <<, then all leading tabs are stripped from word and from the document.

<&digit

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

<&-

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

<&p

The input from the co-process is moved to standard input.

>&p

The output to the co-process is moved to standard output.

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

... 2>&1

means file descriptor 2 is to be opened for writing as a duplicate of file descriptor 1.

The order in which redirections are specified is significant. The shell evaluates each redirection in terms of the (file descriptor, file) association at the time of evaluation. For example:

... 1>fname 2>&1

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

If a command is followed by & and job control is not active, then the default standard input for the command is the empty file /dev/null. Otherwise, the environment for the execution of a command contains the file descriptors of the invoking shell as modified by input/output specifications.

Environment

The environment for any simple-command or function may be augmented by prefixing it with one or more variable assignments. A variable assignment argument is a word of the form identifier=value. Thus:

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

are equivalent (as far as the above execution of cmd is concerned except for special commands listed below that are preceded with a dagger).

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

echo a=b cset -kecho a=b c

This feature is intended for use with scripts written for early versions of the shell and its use in new scripts is strongly discouraged. It is likely to disappear someday.

Functions

The function reserved word, described in the Commands section above, is used to define shell functions. Shell functions are read in and stored internally. Alias names are resolved when the function is read. Functions are executed like commands with the arguments passed as positional parameters. (See Execution below.)

Functions execute in the same process as the caller and share all files and present working directory with the caller. Traps caught by the caller are reset to their default action inside the function. A trap condition that is not caught or ignored by the function causes the function to terminate and the condition to be passed on to the caller. A trap on EXIT set inside a function is executed after the function completes in the environment of the caller. Ordinarily, variables are shared between the calling program and the function. However, the typeset special command used within a function defines local variables whose scope includes the current function and all functions it calls.

The special command return is used to return from function calls. Errors within functions return control to the caller.

The names of all functions can be listed with typeset +f. typeset -f lists all function names as well as the text of all functions. typeset -f function-names lists the text of the named functions only. Functions can be undefined with the -f option of the unset special command.

Ordinarily, functions are unset when the shell executes a shell script. The -xf option of the typeset command allows a function to be exported to scripts that are executed without a separate invocation of the shell. Functions that need to be defined across separate invocations of the shell should be specified in the ENV file with the -xf option of typeset.

Function Definition Command

The format of a function definition command is as follows:

fname() compound-command[io-redirect ...]

The function is named fname; it must be a name. An implementation may allow other characters in a function name as an extension. The implementation will maintain separate name spaces for functions and variables.

The () in the function definition command consists of two operators. Therefore, intermixing blank characters with the fname, (, and ) is allowed, but unnecessary.

The argument compound-command represents a compound command.

When the function is declared, none of the expansions in wordexp will be performed on the text in compound-command or io-redirect; all expansions will be performed as normal each time the function is called. Similarly, the optional io-redirect redirections and any variable assignments within compound-command will be performed during the execution of the function itself, not the function definition.

When a function is executed, it will have the syntax-error and variable-assignment properties described for the special built-in utilities.

The compound-command will be executed whenever the function name is specified as the name of a simple command The operands to the command temporarily will become the positional parameters during the execution of the compound-command; the special parameter # will also be changed to reflect the number of operands. The special parameter 0 will be unchanged. When the function completes, the values of the positional parameters and the special parameter # will be restored to the values they had before the function was executed. If the special built-in return is executed in the compound-command, the function will complete and execution will resume with the next command after the function call.

An example of how a function definition can be used wherever a simple command is allowed:

# If variable i is equal to "yes",

# define function foo to be ls -l

#

[ "$i" = yes ] && foo() {

ls -l

}

The exit status of a function definition will be 0 if the function was declared successfully; otherwise, it will be greater than zero. The exit status of a function invocation will be the exit status of the last command executed by the function.

Jobs

If the monitor option of the set command is turned on, an interactive shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with &, the shell prints a line which looks like:

[1] 1234

indicating that the job, which was started asynchronously, was job number 1 and had one (top-level) process, whose process id was 1234.

If you are running a job and wish to do something else you may hit the key ^Z (CTRL-Z ) which sends a STOP signal to the current job. The shell will then normally indicate that the job has been ‘Stopped’, and print another prompt. You can then manipulate the state of this job, putting it in the background with the bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg. A ^Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed.

A job being run in the background will stop if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by giving the command ‘stty tostop’. If you set this tty option, then background jobs will stop when they try to produce output like they do when they try to read input.

There are several ways to refer to jobs in the shell. A job can be referred to by the process id of any process of the job or by one of the following:

%number

The job with the given number.

%string

Any job whose command line begins with string.

%?string

Any job whose command line contains string.

%%

Current job.

%+

Equivalent to %%.

%-

Previous job.

The shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work.

When the monitor mode is on, each background job that completes triggers any trap set for CHLD .

When you try to leave the shell while jobs are running or stopped, you will be warned that ‘You have stopped(running) jobs.’ You may use the jobs command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated. If you have nohup’ed jobs running when you attempt to logout, you will be warned with the message

You have jobs running.

You will then need to logout a second time to actually logout; however, your background jobs will continue to run.

Signals

Execution

The shell variable PATH defines the search path for the directory containing the command. Alternative directory names are separated by a colon (:). The default path is /bin:/usr/bin: (specifying /bin, /usr/bin, and the current directory in that order). The current directory can be specified by two or more adjacent colons, or by a colon at the beginning or end of the path list. If the command name contains a / then the search path is not used. Otherwise, each directory in the path is searched for an executable file. If the file has execute permission but is not a directory or an a.out file, it is assumed to be a file containing shell commands. A sub-shell is spawned to read it. All non-exported aliases, functions, and variables are removed in this case. A parenthesized command is executed in a sub-shell without removing non-exported quantities.

Command Re-entry

In-line Editing Option

The editing features require that the user’s terminal accept RETURN as carriage return without line feed and that a space must overwrite the current character on the screen.

The editing modes implement a concept where the user is looking through a window at the current line. The window width is the value of COLUMNS if it is defined, otherwise 80. If the window width is too small to display the prompt and leave at least 8 columns to enter input, the prompt is truncated from the left. If the line is longer than the window width minus two, a mark is displayed at the end of the window to notify the user. As the cursor moves and reaches the window boundaries the window will be centered about the cursor. The mark is a > if the line extends on the right side of the window, < if the line extends on the left, and * if the line extends on both sides of the window.

The search commands in each edit mode provide access to the history file. Only strings are matched, not patterns, although a leading ^ in the string restricts the match to begin at the first character in the line.

emacs Editing Mode

The notation for escape sequences is M- followed by a character. For example, M-f (pronounced Meta f) is entered by depressing ESC (ascii 033) followed by ‘f’. (M-F would be the notation for ESC followed by SHIFT (capital) ‘F’.)

All edit commands operate from any place on the line (not just at the beginning). Neither the RETURN nor the LINEFEED key is entered after edit commands except when noted.

^F

Move cursor forward (right) one character.

M-f

Move cursor forward one word. (The emacs editor’s idea of a word is a string of characters consisting of only letters, digits and underscores.)

^B

Move cursor backward (left) one character.

M-b

Move cursor backward one word.

^A

Move cursor to start of line.

^E

Move cursor to end of line.

^]char

Move cursor forward to character char on current line.

M-^]char

Move cursor backward to character char on current line.

^X^X

Interchange the cursor and mark.

erase

(User defined erase character as defined by the stty(1) command, usually ^H or #.) Delete previous character.

^D

Delete current character.

M-d

Delete current word.

M-^H

(Meta-backspace) Delete previous word.

M-h

Delete previous word.

M-^?

(Meta-DEL ) Delete previous word (if your interrupt character is ^? (DEL, the default) then this command will not work).

^T

Transpose current character with next character in emacs mode. Transpose two previous characters in gmacs mode.

^C

Capitalize current character.

M-c

Capitalize current word.

M-l

Change the current word to lower case.

^K

Delete from the cursor to the end of the line. If preceded by a numerical parameter whose value is less than the current cursor position, then delete from given position up to the cursor. If preceded by a numerical parameter whose value is greater than the current cursor position, then delete from cursor up to given cursor position.

^W

Kill from the cursor to the mark.

M-p

Push the region from the cursor to the mark on the stack.

kill

(User defined kill character as defined by the stty(1) command, usually ^G or @.) Kill the entire current line. If two kill characters are entered in succession, all kill characters from then on cause a line feed (useful when using paper terminals).

^Y

Restore last item removed from line. (Yank item back to the line.)

^L

Line feed and print current line.

^@

(null character) Set mark.

M-space

(Meta space) Set mark.

J

(New line) Execute the current line.

M

(Return) Execute the current line.

eof

End-of-file character, normally ^D, is processed as an End-of-file only if the current line is null.

^P

Fetch previous command. Each time ^P is entered the previous command back in time is accessed. Moves back one line when not on the first line of a multi-line command.

M-<

Fetch the least recent (oldest) history line.

M->

Fetch the most recent (youngest) history line.

^N

Fetch next command line. Each time ^N is entered the next command line forward in time is accessed.

^Rstring

Reverse search history for a previous command line containing string. If a parameter of zero is given, the search is forward. string is terminated by a RETURN or NEW LINE . If string is preceded by a ^, the matched line must begin with string. If string is omitted, then the next command line containing the most recent string is accessed. In this case a parameter of zero reverses the direction of the search.

^O

Operate. Execute the current line and fetch the next line relative to current line from the history file.

M-digits

(Escape) Define numeric parameter, the digits are taken as a parameter to the next command. The commands that accept a parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^], M-_, M-b, M-c, M-d, M-f, M-h, M-l and M-^H.

M-letter

Soft-key. Your alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value will be inserted on the input queue. The letter must not be one of the above meta-functions.

M-[letter

Soft-key. Your alias list is searched for an alias by the name __letter and if an alias of this name is defined, its value will be inserted on the input queue. The can be used to program functions keys on many terminals.

M-.

The last word of the previous command is inserted on the line. If preceded by a numeric parameter, the value of this parameter determines which word to insert rather than the last word.

M-_

Same as M-..

M-*

An asterisk is appended to the end of the word and a file name expansion is attempted.

M-ESC

File name completion. Replaces the current word with the longest common prefix of all filenames matching the current word with an asterisk appended. If the match is unique, a / is appended if the file is a directory and a space is appended if the file is not a directory.

M-=

List files matching current word pattern if an asterisk were appended.

^U

Multiply parameter of next command by 4.

\

Escape next character. Editing characters, the user’s erase, kill and interrupt (normally ^?) characters may be entered in a command line or in a search string if preceded by a \. The \ removes the next character’s editing features (if any).

^V

Display version of the shell.

M-#

Insert a # at the beginning of the line and execute it. This causes a comment to be inserted in the history file.

vi Editing Mode

When in vi mode on most systems, canonical processing is initially enabled and the command will be echoed again if the speed is 1200 baud or greater and it contains any control characters or less than one second has elapsed since the prompt was printed. The ESC character terminates canonical processing for the remainder of the command and the user can then modify the command line. This scheme has the advantages of canonical processing with the type-ahead echoing of raw mode.

If the option viraw is also set, the terminal will always have canonical processing disabled. This mode is implicit for systems that do not support two alternate end of line delimiters, and may be helpful for certain terminals.

Input Edit Commands

erase

(User defined erase character as defined by the stty(1) command, usually ^H or #.) Delete previous character.

^W

Delete the previous blank separated word.

^D

Terminate the shell.

^V

Escape next character. Editing characters and the user’s erase or kill characters may be entered in a command line or in a search string if preceded by a ^V. The ^V removes the next character’s editing features (if any).

\

Escape the next erase or kill character.

Motion Edit Commands

[count]l

Cursor forward (right) one character.

[count]w

Cursor forward one alpha-numeric word.

[count]W

Cursor to the beginning of the next word that follows a blank.

[count]e

Cursor to end of word.

[count]E

Cursor to end of the current blank delimited word.

[count]h

Cursor backward (left) one character.

[count]b

Cursor backward one word.

[count]B

Cursor to preceding blank separated word.

[count]|

Cursor to column count.

[count]fc

Find the next character c in the current line.

[count]Fc

Find the previous character c in the current line.

[count]tc

Equivalent to f followed by h.

[count]Tc

Equivalent to F followed by l.

[count];

Repeats count times, the last single character find command, f, F, t, or T.

[count],

Reverses the last single character find command count times.

Cursor to start of line.

^

Cursor to first non-blank character in line.

$

Cursor to end of line.

%

Moves to balancing (, ), {, }, [, or ]. If cursor is not on one of the above characters, the remainder of the line is searched for the first occurrence of one of the above characters first.

Search Edit Commands

[count]k

Fetch previous command. Each time k is entered the previous command back in time is accessed.

[count]-

Equivalent to k.

[count]j

Fetch next command. Each time j is entered the next command forward in time is accessed.

[count]+

Equivalent to j.

[count]G

The command number count is fetched. The default is the least recent history command.

/string

Search backward through history for a previous command containing string. string is terminated by a RETURN or NEWLINE . If string is preceded by a ^, the matched line must begin with string. If string is NULL , the previous string will be used.

?string

Same as / except that search will be in the forward direction.

n

Search for next match of the last pattern to / or ? commands.

N

Search for next match of the last pattern to / or ?, but in reverse direction. Search history for the string entered by the previous / command.

Text Modification Edit Commands

a

Enter input mode and enter text after the current character.

A

Append text to the end of the line. Equivalent to $a.

[count]cmotion

c[count]motion

Delete current character through the character that motion would move the cursor to and enter input mode. If motion is c, the entire line will be deleted and input mode entered.

C

Delete the current character through the end of line and enter input mode. Equivalent to c$.

[count]s

Delete count characters and enter input mode.

S

Equivalent to cc.

D

Delete the current character through the end of line. Equivalent to d$.

[count]dmotion

d[count]motion

Delete current character through the character that motion would move to. If motion is d, the entire line will be deleted.

i

Enter input mode and insert text before the current character.

I

Insert text before the beginning of the line. Equivalent to 0i.

[count]P

Place the previous text modification before the cursor.

[count]p

Place the previous text modification after the cursor.

R

Enter input mode and replace characters on the screen with characters you type overlay fashion.

[count]rc

Replace the count character(s) starting at the current cursor position with c, and advance the cursor.

[count]x

Delete current character.

[count]X

Delete preceding character.

[count].

Repeat the previous text modification command.

[count]~

Invert the case of the count character(s) starting at the current cursor position and advance the cursor.

[count]_

Causes the count word of the previous command to be appended and input mode entered. The last word is used if count is omitted.

*

Causes an * to be appended to the current word and file name generation attempted. If no match is found, it rings the bell. Otherwise, the word is replaced by the matching pattern and input mode is entered.

\

Filename completion. Replaces the current word with the longest common prefix of all filenames matching the current word with an asterisk appended. If the match is unique, a / is appended if the file is a directory and a space is appended if the file is not a directory.

Other Edit Commands

[count]ymotion

y[count]motion

Yank current character through character that motion would move the cursor to and puts them into the delete buffer. The text and cursor are unchanged.

Y

Yanks from current position to end of line. Equivalent to y$.

u

Undo the last text modifying command.

U

Undo all the text modifying commands performed on the line.

[count]v

Returns the command fc -e ${VISUAL :-${EDITOR :-vi}} count in the input buffer. If count is omitted, then the current line is used.

^L

Line feed and print current line. Has effect only in control mode.

J

(New line) Execute the current line, regardless of mode.

M

(Return) Execute the current line, regardless of mode.

#

If the first character of the command is a #, then this command deletes this # and each # that follows a newline. Otherwise, sends the line after inserting a # in front of each line in the command. Useful for causing the current line to be inserted in the history as a comment and removing comments from previous comment commands in the history file.

=

List the file names that match the current word if an asterisk were appended it.

@letter

Your alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value will be inserted on the input queue for processing.

Special Commands

.
1. Variable assignment lists preceding the command remain in effect when the command completes.
.
2. I/O redirections are processed after variable assignments.
.
3. Errors cause a script that contains them to abort.
.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.

* : [ arg ... ]

The command only expands parameters.

* . file [ arg ... ]

Read the complete file then execute the commands. The commands are executed in the current shell environment. The search path specified by PATH is used to find the directory containing file. If any arguments arg are given, they become the positional parameters. Otherwise the positional parameters are unchanged. The exit status is the exit status of the last command executed.

** alias [ -tx ] [ name[ =value ] ] ...

alias with no arguments prints the list of aliases in the form name=value on standard output. An alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution. The -t flag is used to set and list tracked aliases. The value of a tracked alias is the full pathname corresponding to the given name. The value becomes undefined when the value of PATH is reset but the aliases remained tracked. Without the -t flag, for each name in the argument list for which no value is given, the name and value of the alias is printed. The -x flag is used to set or print exported aliases. An exported alias is defined for scripts invoked by name. The exit status is non-zero if a name is given, but no value, and no alias has been defined for the name.

bg [ %job... ]

This command is only on systems that support job control. Puts each specified job into the background. The current job is put in the background if job is not specified. See "Jobs" section above for a description of the format of job.

* break [ n ]

Exit from the enclosed for, while, until, or select loop, if any. If n is specified then break n levels.

* continue [ n ]

Resume the next iteration of the enclosed for, while, until, or select loop. If n is specified then resume at the n-th enclosed loop.

cd [ arg ]

cd old new

This command can be in either of two forms. In the first form it changes the current directory to arg. If arg is - the directory is changed to the previous directory. The shell variable HOME is the default arg. The variable PWD is set to the current directory. The shell variable CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a colon (:). The default path is null (specifying the current directory). Note that 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 arg begins with a / then the search path is not used. Otherwise, each directory in the path is searched for arg.

The second form of cd substitutes the string new for the string old in the current directory name, PWD and tries to change to this new directory.

The cd command may not be executed by rksh.

command [-p] [command_name] [argument ...]

command [-v -V] command_name

The command utility causes the shell to treat the arguments as a simple command, suppressing the shell function lookup. The -p flag performs the command search using a default value for PATH that is guaranteed to find all of the standard utilities. The -v flag writes a string to standard output that indicates the pathname or command that will be used by the shell, in the current shell execution environment, to invoke command_name. The -V flag writes a string to standard output that indicates how the name given in the command_name operand will be interpreted by the shell, in the current shell execution environment.

* eval [ arg ... ]

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

* exec [ arg ... ]

If arg is given, the command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may appear and affect the current process. If no arguments are given the effect of this command is to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program.

* exit [ n ]

Causes the calling shell or shell script to exit with the exit status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the exit status is that of the last command executed. When exit occurs when executing a trap, the last command refers to the command that executed before the trap was invoked. An EOF will also cause the shell to exit except for a shell which has the ignoreeof option (See set below) turned on.

** export [ name[=value] ] ...

The given names are marked for automatic export to the environment of subsequently-executed commands.

fc [ -e ename  ] [ -nlr ] [ first [ last ] ]

fc -e - [ old=new ] [ command ]

In the first form, a range of commands from first to last is selected from the last HISTSIZE commands that were typed at the terminal. The arguments first and last may be specified as a number or as a string. A string is used to locate the most recent command starting with the given string. A negative number is used as an offset to the current command number. If the -l flag is selected, the commands are listed on standard output. Otherwise, the editor program ename is invoked on a file containing these keyboard commands. If ename is not supplied, then the value of the variable FCEDIT (default /bin/ed) is used as the editor. When editing is complete, the edited command(s) is executed. If last is not specified then it will be set to first. If first is not specified the default is the previous command for editing and -16 for listing. The flag -r reverses the order of the commands and the flag -n suppresses command numbers when listing. In the second form the command is re-executed after the substitution old=new is performed. If there is not a command argument, the most recent command typed at this terminal is executed.

fg [ %job... ]

This command is only on systems that support job control. Each job specified is brought to the foreground. Otherwise, the current job is brought into the foreground. See "Jobs" section above for a description of the format of job.

getopts optstring name [ arg ... ]

Checks arg for legal options. If arg is omitted, the positional parameters are used. An option argument begins with a + or a -. An option not beginning with + or - or the argument -- ends the options. optstring contains the letters that getopts recognizes. If a letter is followed by a :, that option is expected to have an argument. The options can be separated from the argument by blanks.

getopts places the next option letter it finds inside variable name each time it is invoked with a + prepended when arg begins with a +. The index of the next arg is stored in OPTIND. The option argument, if any, gets stored in OPTARG.

A leading : in optstring causes getopts to store the letter of an invalid option in OPTARG, and to set name to ? for an unknown option and to : when a required option is missing. Otherwise, getopts prints an error message. The exit status is non-zero when there are no more options. See getoptcvt(1) for usage and description.

hash [ 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 will be done are indicated by an asterisk (*) adjacent to the hits information. Cost will be incremented when the recalculation is done.

jobs [ -lnp ] [ %job ... ]

Lists information about each given job; or all active jobs if job is omitted. The -l flag lists process ids in addition to the normal information. The -n flag displays only jobs that have stopped or exited since last notified. The -p flag causes only the process group to be listed. See "Jobs" section above and jobs(1) for a description of the format of job.

kill [ -sig ] %job ...

kill [ -sig ] pid ...

kill -l

Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in signal(5) 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 will be 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 Jobs for a description of the format of job. In the second form, kill -l, the signal numbers and names are listed.

let arg...

Each arg is a separate arithmetic expression to be evaluated. See the Arithmetic Evaluation section above, for a description of arithmetic expression evaluation.

The exit status is 0 if the value of the last expression is non-zero, and 1 otherwise.

login argument ...

Equivalent to ‘exec login argument....’ See login(1) for usage and description.

* newgrp [ arg ... ]

Equivalent to exec /bin/newgrp arg ....

print [ -Rnprsu[n ] ] [ arg ... ]

The shell output mechanism. With no flags or with flag - or --, the arguments are printed on standard output as described by echo(1) . The exit status is 0, unless the output file is not open for writing.

-n

Suppress NEWLINE from being added to the output.

-R | -r

Raw mode. Ignore the escape conventions of echo. The -R option will print all subsequent arguments and options other than -n.

-p

Write the arguments to the pipe of the process spawned with |& instead of standard output.

-s

Write the arguments to the history file instead of standard output.

-u [ n ]

Specify a one digit file descriptor unit number n on which the output will be placed. The default is 1.

pwd

Equivalent to print -r - $PWD .

read [ -prsu[ n ] ] [ name?prompt ] [ name ... ] The shell input mechanism. One line is read and

is broken up into fields using the characters in IFS as separators. The escape character, (\), is used to remove any special meaning for the next character and for line continuation. In raw mode, -r, the \ character is not treated specially. The first field is assigned to the first name, the second field to the second name, etc., with leftover fields assigned to the last name. The -p option causes the input line to be taken from the input pipe of a process spawned by the shell using |&. If the -s flag is present, the input will be saved as a command in the history file. The flag -u can be used to specify a one digit file descriptor unit n to read from. The file descriptor can be opened with the exec special command. The default value of n is 0. If name is omitted then REPLY is used as the default name. The exit status is 0 unless the input file is not open for reading or an EOF is encountered. An EOF with the -p option causes cleanup for this process so that another can be spawned. If the first argument contains a ?, the remainder of this word is used as a prompt on standard error when the shell is interactive. The exit status is 0 unless an EOF is encountered.

** readonly [ name[=value] ] ...

The given names are marked readonly and these names cannot be changed by subsequent assignment.

* return [ n ]

Causes a shell function or ’.’ script to return to the invoking script with the return status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a ’.’ script, then it is the same as an exit.

set [ +-abCefhkmnopstuvx ] [ +-o option ]...

[ +-A name ] [ arg ... ]
The flags for this command have meaning as follows:

-A

Array assignment. Unset the variable name and assign values sequentially from the list arg. If +A is used, the variable name is not unset first.

-a

All subsequent variables that are defined are automatically exported.

-b

Causes the shell to notify the user asynchronously of background job completions. The following message will be written to standard error:

"[%d]%c %s%s\n", <job-number>, <current>, <status>, <job-name>

where the fields are as follows:

<current>

The character + identifies the job that would be used as a default for the fg or bg utilities; this job can also be specified using the job_id %+ or %%. The character - identifies the job that would become the default if the current default job were to exit; this job can also be specified using the job_id %-. For other jobs, this field is a space character. At most one job can be identified with + and at most one job can be identified with -. If there is any suspended job, then the current job will be a suspended job. If there are at least two suspended jobs, then the previous job will also be a suspended job.

<job-number>

A number that can be used to identify the process group to the wait, fg, bg, and kill utilities. Using these utilities, the job can be identified by prefixing the job number with %.

<status>

Unspecified.

<job-name>

Unspecified.

When the shell notifies the user a job has been completed, it may remove the job’s process ID from the list of those known in the current shell execution environment. Asynchronous notification will not be enabled by default.

-C

Prevent existing files from being overwritten by the shell’s > redirection operator; the >| redirection operator will override this noclobber option for an individual file.

-e

If a command has a non-zero exit status, execute the ERR trap, if set, and exit. This mode is disabled while reading profiles.

-f

Disables file name generation.

-h

Each command becomes a tracked alias when first encountered.

-k

All variable assignment arguments are placed in the environment for a command, not just those that precede the command name.

-m

Background jobs will run in a separate process group and a line will print upon completion. The exit status of background jobs is reported in a completion message. On systems with job control, this flag is turned on automatically for interactive shells.

-n

Read commands and check them for syntax errors, but do not execute them. Ignored for interactive shells.

-o

The following argument can be one of the following option names:

allexport

Same as -a.

errexit

Same as -e.

bgnice

All background jobs are run at a lower priority. This is the default mode.

emacs

Puts you in an emacs style in-line editor for command entry.

gmacs

Puts you in a gmacs style in-line editor for command entry.

ignoreeof

The shell will not exit on EOF . The command exit must be used.

keyword

Same as -k.

markdirs

All directory names resulting from file name generation have a trailing / appended.

monitor

Same as -m.

noclobber

Prevents redirection > from truncating existing files. Require >| to truncate a file when turned on. Equivalent to -C.

noexec

Same as -n.

noglob

Same as -f.

nolog

Do not save function definitions in history file.

notify

Equivalent to -b.

nounset

Same as -u.

privileged

Same as -p.

verbose

Same as -v.

trackall

Same as -h.

vi

Puts you in insert mode of a vi style in-line editor until you hit escape character 033. This puts you in control mode. A return sends the line.

viraw

Each character is processed as it is typed in vi mode.

xtrace

Same as -x.

If no option name is supplied then the current option settings are printed.

-p

Disables processing of the $HOME /.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective uid is not equal to the real uid, or when the effective gid is not equal to the real gid. Turning this off causes the effective uid and gid to be set to the real uid and gid.

-s

Sort the positional parameters lexicographically.

-t

Exit after reading and executing one command.

-u

Treat unset parameters as an error when substituting.

-v

Print shell input lines as they are read.

-x

Print commands and their arguments as they are executed.

-

Turns off -x and -v flags and stops examining arguments for flags.

--

Do not change any of the flags; useful in setting $1 to a value beginning with -. If no arguments follow this flag then the positional parameters are unset.

Using + rather than - causes these flags to be turned off. These flags can also be used upon invocation of the shell. The current set of flags may be found in $-. Unless -A is specified, the remaining arguments are positional parameters and are assigned, in order, to $1 $2 .... If no arguments are given then the names and values of all variables are printed on the standard output.

* shift [ n ]

The positional parameters from $n+1 $n+1 ... are renamed $1 ..., default n is 1. The parameter n can be any arithmetic expression that evaluates to a non-negative number less than or equal to $#.

stop %jobid ...

stop pid ...

stop stops the execution of a background job(s) by using its jobid, or of any process by using its pid. (see ps(1) ).

suspend

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

test expression

Evaluate conditional expressions. See Conditional Expressions section above and test(1) for usage and description.

* times

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

* trap [ arg sig ... ]

arg is a command to be read and executed when the shell receives signal(s) sig. arg is scanned once when the trap is set and once when the trap is taken. sig can be specified as a signal number or signal name. trap commands are executed in order of signal number. Any attempt to set a trap on a signal number that was ignored on entry to the current shell is ineffective.

If arg is -, the shell will reset each sig to the default value. If arg is null (’’), the shell will ignore each specified sig if it arises. Otherwise, arg will be read and executed by the shell when one of the corresponding sigs arises. The action of the trap will override a previous action (either default action or one explicitly set). The value of $? after the trap action completes will be the value it had before the trap was invoked.

sig can be EXIT , 0 (equivalent to EXIT ) or a signal specified using a symbolic name, without the SIG prefix, for example, HUP , INT , QUIT , TERM . If sig is 0 or EXIT and the trap statement is executed inside the body of a function, then the command arg is executed after the function completes. If sig is 0 or EXIT for a trap set outside any function then the command arg is executed on exit from the shell. If sig is ERR then arg will be executed whenever a command has a non-zero exit status. If sig is DEBUG then arg will be executed after each command.

The environment in which the shell executes a trap on EXIT will be identical to the environment immediately after the last command executed before the trap on EXIT was taken.

Each time the trap is invoked, arg will be processed in a manner equivalent to:

eval "$arg"

Signals that were ignored on entry to a non-interactive shell cannot be trapped or reset, although no error need be reported when attempting to do so. An interactive shell may reset or catch signals ignored on entry. Traps will remain in place for a given shell until explicitly changed with another trap command.

When a subshell is entered, traps are set to the default args. This does not imply that the trap command cannot be used within the subshell to set new traps.

The trap command with no arguments will write to standard output a list of commands associated with each sig. The format is:

trap -- %s %s ... <arg>, <sig> ...

The shell will format the output, including the proper use of quoting, so that it is suitable for reinput to the shell as commands that achieve the same trapping results. For example:

save_traps=$(trap)...eval "$save_traps"

If the trap name or number is invalid, a non-zero exit status will be returned; otherwise, 0 will be returned. For both interactive and non-interactive shells, invalid signal names or numbers will not be considered a syntax error and will not cause the shell to abort.

Traps are not processed while a job is waiting for a foreground process. Thus, a trap on CHLD won’t be executed until the foreground job terminates.

type name ...

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

** typeset [ ±HLRZfilrtux[n] ] [ name[=value ] ] ...

Sets attributes and values for shell variables and functions. When typeset is invoked inside a function, a new instance of the variables name is created. The variables value and type are restored when the function completes. The following list of attributes may be specified:

-H

This flag provides UNIX to host-name file mapping on non-UNIX machines.

-L

Left justify and remove leading blanks from value. If n is non-zero it defines the width of the field; otherwise, it is determined by the width of the value of first assignment. When the variable is assigned to, it is filled on the right with blanks or truncated, if necessary, to fit into the field. Leading zeros are removed if the -Z flag is also set. The -R flag is turned off.

-R

Right justify and fill with leading blanks. If n is non-zero it defines the width of the field, otherwise it is determined by the width of the value of first assignment. The field is left filled with blanks or truncated from the end if the variable is reassigned. The -L flag is turned off.

-Z

Right justify and fill with leading zeros if the first non-blank character is a digit and the -L flag has not been set. If n is non-zero it defines the width of the field; otherwise, it is determined by the width of the value of first assignment.

-f

The names refer to function names rather than variable names. No assignments can be made and the only other valid flags are -t, -u and -x. The flag -t turns on execution tracing for this function. The flag -u causes this function to be marked undefined. The FPATH variable will be searched to find the function definition when the function is referenced. The flag -x allows the function definition to remain in effect across shell procedures invoked by name.

-i

Parameter is an integer. This makes arithmetic faster. If n is non-zero it defines the output arithmetic base; otherwise, the first assignment determines the output base.

-l

All upper-case characters are converted to lower-case. The upper-case flag, -u is turned off.

-r

The given names are marked readonly and these names cannot be changed by subsequent assignment.

-t

Tags the variables. Tags are user definable and have no special meaning to the shell.

-u

All lower-case characters are converted to upper-case characters. The lower-case flag, -l is turned off.

-x

The given names are marked for automatic export to the environment of subsequently-executed commands.

The -i attribute can not be specified along with -R,
-L, -Z, or -f.

Using + rather than - causes these flags to be turned off. If no name arguments are given but flags are specified, a list of names (and optionally the values) of the variables which have these flags set is printed. (Using + rather than - keeps the values from being printed.) If no names and flags are given, the names and attributes of all variables are printed.

ulimit [ -HSacdfnstv ] [ limit ]

Set or display a resource limit. The available resources limits are listed below. Many systems do not contain one or more of these limits. The limit for a specified resource is set when limit is specified. The value of limit can be a number in the unit specified below with each resource, or the value unlimited. The H and S flags specify whether the hard limit or the soft limit for the given resource is set. A hard limit cannot be increased once it is set. A soft limit can be increased up to the value of the hard limit. If neither the H or S options is specified, the limit applies to both. The current resource limit is printed when limit is omitted. In this case the soft limit is printed unless H is specified. When more that one resource is specified, then the limit name and unit is printed before the value.

-a

Lists all of the current resource limits.

-c

The number of 512-byte blocks on the size of core dumps.

-d

The number of K-bytes on the size of the data area.

-f

The number of 512-byte blocks on files written by child processes (files of any size may be read).

-n

The number of file descriptors plus 1.

-s

The number of K-bytes on the size of the stack area.

-t

The number of seconds to be used by each process.

-v

The number of K-bytes for virtual memory.

If no option is given, -f is assumed.

umask [-S] [ mask ]

The user file-creation mask is set to mask (see umask(2) ). mask can either be an octal number or a symbolic value as described in chmod(1) . If a symbolic value is given, the new umask value is the complement of the result of applying mask to the complement of the previous umask value. If mask is omitted, the current value of the mask is printed. The -S flag produces symbolic output.

unalias name...

The aliases given by the list of names are removed from the alias list.

unset [ -f ] name ...

The variables given by the list of names are unassigned, that is, their values and attributes are erased. readonly variables cannot be unset. If the -f, flag is set, then the names refer to function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes their special meaning even if they are subsequently assigned to.

* wait [ job ]

Wait for the specified job and report its termination status. If job is not given then all currently active child processes are waited for. The exit status from this command is that of the process waited for. See Jobs for a description of the format of job.

whence [ -pv ] name ...

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

The -v flag produces a more verbose report.

The -p flag does a path search for name even if name is an alias, a function, or a reserved word.

Invocation

-c string

If the -c flag is present then commands are read from string.

-s

If the -s flag is present or if no arguments remain then commands are read from the standard input. Shell output, except for the output of the Special Commands listed above, is written to file descriptor 2.

-i

If the -i flag is present or if the shell input and output are attached to a terminal (as told by ioctl(2) ) then this shell is interactive. In this case TERM is ignored (so that kill 0 does not kill an interactive shell) and INTR is caught and ignored (so that wait is interruptible). In all cases, QUIT is ignored by the shell.

-r

If the -r flag is present the shell is a restricted shell.

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

rksh Only

• changing directory (see cd(1) )
• setting the value of SHELL, ENV, or PATH
• specifying path or command names containing /
• redirecting output (>, >|, <>, and >>)
• changing group (see newgrp(1) ).

The restrictions above are enforced after .profile and the ENV files are interpreted.

When a command to be executed is found to be a shell procedure, rksh invokes ksh to execute it. Thus, it is possible to provide to the end-user shell procedures that have access to the full power of the standard shell, while imposing a limited menu of commands; this scheme assumes that the end-user does not have write and execute permissions in the same directory.

The net effect of these rules is that the writer of the .profile has complete control over user actions, by performing guaranteed setup actions and leaving the user in an appropriate directory (probably not the login directory).

The system administrator often sets up a directory of commands (that is, /usr/rbin) that can be safely invoked by rksh.

Errors

For a non-interactive shell, an error condition encountered by a special built-in or other type of utility will cause the shell to write a diagnostic message to standard error and exit as shown in the following table:

Error	Special Built-in	Other Utilities
Shell language syntax error	will exit	will exit
Utility syntax error
(option or operand error)	will exit	will not exit
Redirection error	will exit	will not exit
Variable assignment error	will exit	will not exit
Expansion error	will exit	will exit
Command not found	n/a	may exit
Dot script not found	will exit	n/a

An expansion error is one that occurs when the shell expansions are carried out (for example, ${x!y}, because ! is not a valid operator); an implementation may treat these as syntax errors if it is able to detect them during tokenization, rather than during expansion.

If any of the errors shown as ‘will (may) exit’ occur in a subshell, the subshell will (may) exit with a non-zero status, but the script containing the subshell will not exit because of the error.

In all of the cases shown in the table, an interactive shell will write a diagnostic message to standard error without exiting.

Exit Status

If a command is not found, the exit status will be 127. If the command name is found, but it is not an executable utility, the exit status will be 126. Applications that invoke utilities without using the shell should use these exit status values to report similar errors.

If a command fails during word expansion or redirection, its exit status will be greater than zero.

When reporting the exit status with the special parameter ?, the shell will report the full eight bits of exit status available. The exit status of a command that terminated because it received a signal will be reported as greater than 128.

Files

See Also

Morris I. Bolsky and David G. Korn, The KornShell Command and Programming Language, Prentice Hall, 1989.

Warnings

Notes

If a command which is a tracked alias is executed, and then 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 will continue to exec the original command. Use the -t option of the alias command to correct this situation.

Some very old shell scripts contain a ^ as a synonym for the pipe character |.

Using the fc built-in command within a compound command will cause the whole command to disappear from the history file.

The built-in command . file reads the whole file before any commands are executed. Therefore, alias and unalias commands in the file will not apply to any functions defined in the file.

Table of Contents

• Name
• Synopsis
• Availability
• /usr/bin/ksh
• /usr/bin/rksh
• /usr/xpg4/bin/sh
• Description
• Definitions
• Commands
• Comments
• Aliasing
• Tilde Substitution
• Tilde Expansion
• Command Substitution
• Arithmetic Expansion
• Process Substitution
• Parameter Substitution
• Parameter Expansion
• Parameters Set by Shell
• Variables Used by Shell
• Blank Interpretation
• File Name Generation
• Quoting
• Arithmetic Evaluation
• Prompting
• Conditional Expressions
• Input/Output
• Environment
• Functions
• Function Definition Command
• Jobs
• Signals
• Execution
• Command Re-entry
• In-line Editing Option
• emacs Editing Mode
• vi Editing Mode
• Input Edit Commands
• Motion Edit Commands
• Search Edit Commands
• Text Modification Edit Commands
• Other Edit Commands
• Special Commands
• Invocation
• rksh Only
• Errors
• Exit Status
• Files
• See Also
• Warnings
• Notes