KSH

ksh, rksh, pfksh − KornShell, a standard/restricted command and programming language

ksh [ ±abcefhiknoprstuvxBCDP ] [ −R file ] [ ±o option ] ... [ − ] [ arg ... ]

Ksh is a command and programming language that executes commands read from a terminal or a file. Rksh is a restricted version of the command interpreter ksh; it is used to set up login names and execution environments whose capabilities are more controlled than those of the standard shell. Rpfksh is a profile shell version of the command interpreter ksh; it is used to to execute commands with the attributes specified by the user’s profiles (see pfexec(1)). See Invocation below for the meaning of arguments to the shell.

Definitions.

A metacharacter is one of the following characters:

; & ( ) │ < > new-line 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 components of variable names. A vname is a sequence of one or more identifiers separated by a . and optionally preceded by a . . Vnames are used as function and variable names. A word is a sequence of characters from the character set defined by the current locale, excluding 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 built-in command is a command that is carried out by the shell itself without creating a separate process. Some commands are built-in purely for convenience and are not documented here. Built-ins that cause side effects in the shell environment and built-ins that are found before performing a path search (see Execution below) are documented here. For historical reasons, some of these built-ins behave differently than other built-ins and are called special built-ins.

Commands.

A simple-command is a list of variable assignments (see Variable Assignments below) or a sequence of blank separated words which may be preceded by a list of variable assignments (see Environment below). The first word specifies the name of the command to be executed. Except as specified below, the remaining words are passed as arguments to the invoked command. The command name is passed as argument 0 (see exec(2)). The value of a simple-command is its exit status; 0-255 if it terminates normally; 256+signum if it terminates abnormally (the name of the signal corresponding to the exit status can be obtained via the −l option of the kill built-in utility).

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, except possibly the last, 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 unless the pipefail option is enabled. Each pipeline can be preceded by the reserved word ! which causes the exit status of the pipeline to become 0 if the exit status of the last command is non-zero, and 1 if the exit status of the last command is 0.

A list is a sequence of one or more pipelines separated by ;, &, │&, &&, or ││, and optionally terminated by ;, &, or │&. Of these 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 (i.e., the shell does not wait for that pipeline to finish). The symbol │& causes asynchronous execution of the preceding pipeline with a two-way pipe established to the parent shell; the standard input and output of the spawned pipeline can be written to and read from by the parent shell by applying the redirection operators <& and >& with arg p to commands and by using −p option of the built-in commands read and print described later. The symbol && (││) causes the list following it to be executed only if the preceding pipeline returns a zero (non-zero) value. One or more new-lines may appear in a list instead of a semicolon, to delimit a command. The first item of the first pipeline of a list that is a simple command not beginning with a redirection, and not occurring within a while, until, or if list, can be preceded by a semicolon. This semicolon is ignored unless the showme option is enabled as described with the set built-in below.

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

Each time a for command is executed, vname 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 starting from 1 (see Parameter Expansion below). Execution ends when there are no more words in the list.

for (( [expr1] ; [expr2] ; [expr3] )) ;do list ;done

The arithmetic expression expr1 is evaluated first (see Arithmetic evaluation below). The arithmetic expression expr2 is repeatedly evaluated until it evaluates to zero and when non-zero, list is executed and the arithmetic expression expr3 evaluated. If any expression is omitted, then it behaves as if it evaluated to 1.

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

A select command prints on standard error (file descriptor 2) the set of words, each preceded by a number. If in word ... is omitted, then the positional parameters starting from 1 are used instead (see Parameter Expansion 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 vname 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 vname is set to null. The contents of the line read from standard input is saved in the variable REPLY. The list is executed for each selection until a break or end-of-file 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). The ;; operator causes execution of case to terminate. If ;& is used in place of ;; the next subsequent list, if any, is executed.

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

The list following if is executed and, if it returns a zero exit status, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is zero, the list following the next then is executed. Failing each successive elif list, the else list is executed. If the if list has non-zero exit status and there is no else list, then the if command returns a zero exit status.

while list ;do list ;done

until list ;do list ;done

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

((expression))

The expression is evaluated using the rules for arithmetic evaluation described below. If the value of the arithmetic expression is non-zero, the exit status is 0, otherwise the exit status is 1.

(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 evaluation as an arithmetic command as described above.

{ 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 a zero exit status when expression is true. See Conditional Expressions below, for a description of expression.

function varname { list ;}

varname () { list ;}

Define a function which is referenced by varname. A function whose varname contains a . is called a discipline function and the portion of the varname preceding the last . must refer to an existing variable. The body of the function is the list of commands between { and }. A function defined with the function varname syntax can also be used as an argument to the . special built-in command to get the equivalent behavior as if the varname() syntax were used to define it. (See Functions below.)

time [ pipeline ]

If pipeline is omitted the user and system time for the current shell and completed child processes is printed on standard error. Otherwise, pipeline is executed and the elapsed time as well as the user and system time are printed on standard error. The TIMEFORMAT variable may be set to a format string that specifies how the timing information should be displayed. See Shell Variables below for a description of the TIMEFORMAT variable.

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

if then else elif fi case esac for while until do done { } function select time [[ ]] !

Variable Assignments.

One or more variable assignments can start a simple command or can be arguments to the typeset, enum, export, or readonly special built-in commands as well as to other declaration commands created as types. The syntax for an assignment is of the form:

varname=word

varname[word]=word

No space is permitted between varname and the = or between = and word.

varname=(assign_list)

No space is permitted between varname and the =. An assign_list can be one of the following:

word ...

Indexed array assignment.

[word]=word ...

Associative array assignment. If preceded by typeset −a this will create an indexed array instead.

assignment ...

Compound variable assignment. This creates a compound variable varname with sub-variables of the form varname.name, where name is the name portion of assignment. The value of varname will contain all the assignment elements. Additional assignments made to sub-variables of varname will also be displayed as part of the value of varname. If no assignments are specified, varname will be a compound variable allowing subsequence child elements to be defined.

typeset [options] assignment ...

Nested variable assignment. Multiple assignments can be specified by separating each of them with a ;. The previous value is unset before the assignment. Other declaration commands such as readonly, enum, and other declaration commands can be used in place of typeset.

. filename

Include the assignment commands contained in filename.

In addition, a += can be used in place of the = to signify adding to or appending to the previous value. When += is applied to an arithmetic type, word is evaluated as an arithmetic expression and added to the current value. When applied to a string variable, the value defined by word is appended to the value. For compound assignments, the previous value is not unset and the new values are appended to the current ones provided that the types are compatible.

The right hand side of a variable assignment undergoes all the expansion listed below except word splitting, brace expansion, and file name generation. When the left hand side is an assignment is a compound variable and the right hand is the name of a compound variable, the compound variable on the right will be copied or appended to the compound variable on the left.

Comments.

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

Aliasing.

The first word of each command is replaced by the text of an alias if an alias for this word has been defined. An alias name consists of any number of characters excluding metacharacters, quoting characters, file expansion characters, parameter expansion and command substitution characters, and =. The replacement string can contain any valid shell script including the metacharacters listed above. The first word of each command in the replaced text, other than any that are in the process of being replaced, will be tested for aliases. If the last character of the alias value is a blank then the word following the alias will also be checked for alias substitution. Aliases can be used to redefine built-in commands but cannot be used to redefine the reserved words listed above. Aliases can be created and listed with the alias command and can be removed with the unalias command.
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.
The following aliases are compiled into the shell but can be unset or redefined:

autoload=′typeset −fu′

command=′command ′

compound=′typeset −C′

fc=hist

float=′typeset −lE′

functions=′typeset −f′

hash=′alias −t −−′

history=′hist −l′

integer=′typeset −li′

nameref=′typeset −n′

nohup=′nohup ′

r=′hist −s′

redirect=′command exec′

source=′command . ′

stop=′kill −s STOP ′

suspend=′kill −s STOP $$′

times=′{ { time;} 2>&1;}′

type=′whence −v′

Tilde Substitution.

After alias substitution is performed, each word is checked to see if it begins with an unquoted ∼. For tilde substitution, word also refers to the word portion of parameter expansion (see Parameter Expansion below). If it does, then the word up to a / is checked to see if it matches a user name in the password database (See getpwname(3).) If a match is found, the ∼ and the matched login name are replaced by the login directory of the matched user. If no match is found, the original text is left unchanged. A ∼ by itself, or in front of a /, is replaced by $HOME. A ∼ followed by a + or − is replaced by the value of $PWD and $OLDPWD respectively.

In addition, when expanding a variable assignment, tilde substitution is attempted when the value of the assignment begins with a ∼, and when a ∼ appears after a :. The : also terminates a ∼ login name.

Command Substitution.

The standard output from a command list enclosed in parentheses preceded by a dollar sign ( $(list) ), or in a brace group preceded by a dollar sign ( ${ list;} ), or in a pair of grave accents ( `` ) may be used as part or all of a word; trailing new-lines are removed. In the second case, the { and } are treated as a reserved words so that { must be followed by a blank and } must appear at the beginning of the line or follow a ;. In the third (obsolete) form, the string between the quotes is processed for special quoting characters before the command is executed (see Quoting below). The command substitution $(cat file) can be replaced by the equivalent but faster $(<file). The command substitution $(n<#) will expand to the current byte offset for file descriptor n. Except for the second form, the command list is run in a subshell so that no side effects are possible. For the second form, the final } will be recognized as a reserved word after any token.

Arithmetic Substitution.

An arithmetic expression enclosed in double parentheses preceded by a dollar sign ( $(()) ) is replaced by the value of the arithmetic expression within the double parentheses.

Process Substitution.

This feature is only available on versions of the UNIX operating system that support the /dev/fd directory for naming open files. Each command argument of the form <(list) or >(list) will run process list asynchronously connected to some file in /dev/fd. The name of this file will become the argument to the command. If the form with > is selected then writing on this file will provide input for list. If < is used, then the file passed as an argument will contain the output of the list process. For example,

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.

Process substitution of the form <(list) can also be used with the < redirection operator which causes the output of list to be standard input or the input for whatever file descriptor is specified.

Parameter Expansion.

A parameter is a variable, one or more digits, or any of the characters ∗, @, #, ?, −, $, and !. A variable is denoted by a vname. To create a variable whose vname contains a . , a variable whose vname consists of everything before the last . must already exist. A variable has a value and zero or more attributes. Variables can be assigned values and attributes by using the typeset special built-in command. The attributes supported by the shell are described later with the typeset special built-in command. Exported variables pass values and attributes to the environment.

The shell supports both indexed and associative arrays. An element of an array variable is referenced by a subscript. A subscript for an indexed array is denoted by an arithmetic expression (see Arithmetic evaluation below) between a [ and a ]. To assign values to an indexed array, use vname=(value ...) or set −A vname value ... . The value of all non-negative subscripts must be in the range of 0 through 4,194,303. A negative subscript is treated as an offset from the maximum current index +1 so that −1 refers to the last element. Indexed arrays can be declared with the −a option to typeset. Indexed arrays need not be declared. Any reference to a variable with a valid subscript is legal and an array will be created if necessary.

An associative array is created with the −A option to typeset. A subscript for an associative array is denoted by a string enclosed between [ and ].

Referencing any array without a subscript is equivalent to referencing the array with subscript 0.

The value of a variable may be assigned by writing:

vname=value [ vname=value ] ...

or

vname[subscript]=value [ vname[subscript]=value ] ...

Note that no space is allowed before or after the =.
A nameref is a variable that is a reference to another variable. A nameref is created with the −n attribute of typeset. The value of the variable at the time of the typeset command becomes the variable that will be referenced whenever the nameref variable is used. The name of a nameref cannot contain a . . When a variable or function name contains a . , and the portion of the name up to the first . matches the name of a nameref, the variable referred to is obtained by replacing the nameref portion with the name of the variable referenced by the nameref. If a nameref is used as the index of a for loop, a name reference is established for each item in the list. A nameref provides a convenient way to refer to the variable inside a function whose name is passed as an argument to a function. For example, if the name of a variable is passed as the first argument to a function, the command

typeset −n var=$1

inside the function causes references and assignments to var to be references and assignments to the variable whose name has been passed to the function.
If any of the floating point attributes, −E, −F, or −X, or the integer attribute, −i, is set for vname, then 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 built-in command. Parameter $0 is set from argument zero when the shell is invoked.
The character $ is used to introduce substitutable parameters.

${parameter}

The shell reads all the characters from ${ to the matching } as part of the same word even if it contains braces or metacharacters. The value, if any, of the parameter is substituted. The braces are required when parameter is followed by a letter, digit, or underscore that is not to be interpreted as part of its name, when the variable name contains a . . The braces are also required when a variable is subscripted unless it is part of an Arithmetic Expression or a Conditional Expression. 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. If parameter is ∗ or @, then all the positional parameters, starting with $1, are substituted (separated by a field separator character). If an array vname with subscript ∗ @, or of the form sub1 .. sub2. is used, then the value for each of the elements between sub1 and sub2 inclusive (or all elements for ∗ and @) is substituted, separated by the first character of the value of IFS.

${#parameter}

If parameter is ∗ or @, the number of positional parameters is substituted. Otherwise, the length of the value of the parameter is substituted.

${#vname[*]}

${#vname[@]}

The number of elements in the array vname is substituted.

${@vname}

Expands to the type name (See Type Variables below) or attributes of the variable referred to by vname.

${!vname}

Expands to the name of the variable referred to by vname. This will be vname except when vname is a name reference.

${!vname[subscript]}

Expands to name of the subscript unless subscript is *, @. or of the form sub1 .. sub2. When subscript is *, the list of array subscripts for vname is generated. For a variable that is not an array, the value is 0 if the variable is set. Otherwise it is null. When subscript is @, same as above, except that when used in double quotes, each array subscript yields a separate argument. When subscript is of the form sub1 .. sub2 it expands to the list of subscripts between sub1 and sub2 inclusive using the same quoting rules as @.

${!prefix*}

Expands to the names of the variables whose names begin with prefix.

${parameter:−word}

If parameter is set and is non-null then substitute its value; otherwise substitute word.

${parameter:=word}

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

${parameter:?word}

If parameter is set and is non-null then substitute its value; otherwise, print word and exit from the shell (if not interactive). If word is omitted then a standard message is printed.

${parameter:+word}

If parameter is set and is non-null then substitute word; otherwise substitute nothing.

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

print ${d:−$(pwd)}

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

${parameter:offset:length}

${parameter:offset}

Expands to the portion of the value of parameter starting at the character (counting from 0) determined by expanding offset as an arithmetic expression and consisting of the number of characters determined by the arithmetic expression defined by length. In the second form, the remainder of the value is used. If A negative offset counts backwards from the end of parameter. Note that one or more blanks is required in front of a minus sign to prevent the shell from interpreting the operator as :−. If parameter is ∗ or @, or is an array name indexed by ∗ or @, then offset and length refer to the array index and number of elements respectively. A negative offset is taken relative to one greater than the highest subscript for indexed arrays. The order for associate arrays is unspecified.

${parameter#pattern}

${parameter##pattern}

If the shell pattern matches the beginning of the value of parameter, then the value of this expansion is the value of the parameter with the matched portion deleted; otherwise the value of this parameter is substituted. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted. When parameter is @, *, or an array variable with subscript @ or *, the substring operation is applied to each element in turn.

${parameter%pattern}

${parameter%%pattern}

If the shell pattern matches the end of the value of parameter, then the value of this expansion is the value of the parameter with the matched part deleted; otherwise substitute the value of parameter. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted. When parameter is @, *, or an array variable with subscript @ or *, the substring operation is applied to each element in turn.

${parameter/pattern/string}

${parameter//pattern/string}

${parameter/#pattern/string}

${parameter/%pattern/string}

Expands parameter and replaces the longest match of pattern with the given string. Each occurrence of \n in string is replaced by the portion of parameter that matches the n-th sub-pattern. In the first form, only the first occurrence of pattern is replaced. In the second form, each match for pattern is replaced by the given string. The third form restricts the pattern match to the beginning of the string while the fourth form restricts the pattern match to the end of the string. When string is null, the pattern will be deleted and the / in front of string may be omitted. When parameter is @, *, or an array variable with subscript @ or *, the substitution operation is applied to each element in turn. In this case, the string portion of word will be re-evaluated for each element.

The following parameters are automatically set by the shell:

#

The number of positional parameters in decimal.

−

Options supplied to the shell on invocation or by 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. While defining a compound variable or a type, _ is initialized as a reference to the compound variable or type. When a discipline function is invoked, _ is initialized as a reference to the variable associated with the call to this function. Finally when _ is used as the name of the first variable of a type definition, the new type is derived from the type of the first variable (See Type Variables below.).

!

The process number of the last background command invoked or the most recent job put in the background with the bg built-in command.

.sh.command

When processing a DEBUG trap, this variable contains the current command line that is about to run.

.sh.edchar

This variable contains the value of the keyboard character (or sequence of characters if the first character is an ESC, ascii 033) that has been entered when processing a KEYBD trap (see Key Bindings below). If the value is changed as part of the trap action, then the new value replaces the key (or key sequence) that caused the trap.

.sh.edcol

The character position of the cursor at the time of the most recent KEYBD trap.

.sh.edmode

The value is set to ESC when processing a KEYBD trap while in vi insert mode. (See Vi Editing Mode below.) Otherwise, .sh.edmode is null when processing a KEYBD trap.

.sh.edtext

The characters in the input buffer at the time of the most recent KEYBD trap. The value is null when not processing a KEYBD trap.

.sh.file

The pathname of the file than contains the current command.

.sh.fun

The name of the current function that is being executed.

.sh.level

Set to the current function depth. This can be changed inside a DEBUG trap and will set the context to the specified level.

.sh.lineno

Set during a DEBUG trap to the line number for the caller of each function.

.sh.match

An indexed array which stores the most recent match and sub-pattern matches after conditional pattern matches that match and after variables expansions using the operators #, %, or /. The 0-th element stores the complete match and the i-th. element stores the i-th submatch. The .sh.match variable becomes unset when the variable that has expanded is assigned a new value.

.sh.name

Set to the name of the variable at the time that a discipline function is invoked.

.sh.subscript

Set to the name subscript of the variable at the time that a discipline function is invoked.

.sh.subshell

The current depth for subshells and command substitution.

.sh.value

Set to the value of the variable at the time that the set or append discipline function is invoked.

.sh.version

Set to a value that identifies the version of this shell.

KSH_VERSION

A name reference to .sh.version.

LINENO

The current line number 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 built-in command.

OPTIND

The index of the last option argument processed by the getopts built-in 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 built-in 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.

SHLVL

An integer variable the is incremented each time the shell is invoked and is exported. If SHLVL is not in the environment when the shell is invoked, it is set to 1.

The following variables are used by the 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 VISUAL variable is not set, the value of this variable will be checked for the patterns as described with VISUAL below and the corresponding editing option (see Special Command set below) will be turned on.

ENV

If this variable is set, then parameter expansion, command substitution, and arithmetic substitution are performed on the value to generate the pathname of the script that will be executed when the shell is invoked interactively (see Invocation below). This file is typically used for alias and function definitions. The default value is $HOME/.kshrc. On systems that support a system wide /etc/ksh.kshrc initialization file, if the filename generated by the expansion of ENV begins with /./ or ././ the system wide initialization file will not be executed.

Obsolete name for the default editor name for the hist command. FCEDIT is not used when HISTEDIT is set.

FIGNORE

A pattern that defines the set of filenames that will be ignored when performing filename matching.

FPATH

The search path for function definitions. The directories in this path are searched for a file with the same name as the function or command when a function with the −u attribute is referenced and when a command is not found. If an executable file with the name of that command is found, then it is read and executed in the current environment. Unlike PATH, the current directory must be represented explicitly by . rather than by adjacent : characters or a beginning or ending :.

HISTCMD

Number of the current command in the history file.

HISTEDIT

Name for the default editor name for the hist command.

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 512.

HOME

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

IFS

Internal field separators, normally space, tab, and new-line that are used to separate the results of command substitution or parameter expansion and to separate fields with the built-in command read. The first character of the IFS variable is used to separate arguments for the "$∗" substitution (see Quoting below). Each single occurrence of an IFS character in the string to be split, that is not in the isspace character class, and any adjacent characters in IFS that are in the isspace character class, delimit a field. One or more characters in IFS that belong to the isspace character class, delimit a field. In addition, if the same isspace character appears consecutively inside IFS, this character is treated as if it were not in the isspace class, so that if IFS consists of two tab characters, then two adjacent tab characters delimit a null field.

JOBMAX

This variable defines the maximum number running background jobs that can run at a time. When this limit is reached, the shell will wait for a job to complete before staring a new job.

LANG

This variable determines the locale category for any category not specifically selected with a variable starting with LC_ or LANG.

LC_ALL

This variable overrides the value of the LANG variable and any other LC_ variable.

LC_COLLATE

This variable determines the locale category for character collation information.

LC_CTYPE

This variable determines the locale category for character handling functions. It determines the character classes for pattern matching (see File Name Generation below).

LC_NUMERIC

This variable determines the locale category for the decimal point character.

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 expansion, command substitution, and arithmetic substitution with the variable $_ defined as the name of the file that has changed. The default message is you have mail in $_.

PATH

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

PS1

The value of this variable is expanded for parameter expansion, command substitution, and arithmetic 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 evaluation, command substitution, and arithmetic substitution and precedes each line of an execution trace. By default, PS4 is ‘‘+ ’’. In addition when PS4 is unset, the execution trace prompt is also ‘‘+ ’’.

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. If it is pfsh or pfksh, then the shell becomes a profile shell (see pfexec(1)).

TIMEFORMAT

The value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with the time reserved word should be displayed. The % character introduces a format sequence that is expanded to a time value or other information. The format sequences and their meanings are as follows.

%%

A literal %.

%[p][l]R

The elapsed time in seconds.

%[p][l]U

The number of CPU seconds spent in user mode.

%[p][l]S

The number of CPU seconds spent in system mode.

%P

The CPU percentage, computed as (U + S) / R.

The brackets denote optional portions. The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point can be displayed; values of p greater than 3 are treated as 3. If p is not specified, the value 3 is used.

The optional l specifies a longer format, including hours if greater than zero, minutes, and seconds of the form HHhMMmSS.FFs. The value of p determines whether or not the fraction is included.

All other characters are output without change and a trailing newline is added. If unset, the default value, $’\nreal\t%2lR\nuser\t%2lU\nsys%2lS’, is used. If the value is null, no timing information is displayed.

TMOUT

If set to a value greater than zero, TMOUT will be the default timeout value for the read built-in command. The select compound command terminates after TMOUT seconds when input is from a terminal. Otherwise, the shell will terminate if a line is not entered within the prescribed number of seconds while reading from a terminal. (Note that the shell can be compiled with a maximum bound for this value which cannot be exceeded.)

If the value of this variable matches the pattern *[Vv][Ii]*, then the vi option (see Special Command set below) is turned on. If the value matches the pattern *gmacs* , the gmacs option is turned on. If the value matches the pattern *macs*, then the emacs option will be turned on. The value of VISUAL overrides the value of EDITOR.

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(1).

Field Splitting.

After parameter expansion and command substitution, the results of substitutions are scanned for the field separator characters (those found in IFS ) and split into distinct fields where such characters are found. Explicit null fields ("" or ′′) are retained. Implicit null fields (those resulting from parameters that have no values or command substitutions with no output) are removed.

If the braceexpand (−B) option is set then each of the fields resulting from IFS are checked to see if they contain one or more of the brace patterns {*,*}, {l1..l2} , {n1..n2} , {n1..n2% fmt} , {n1..n2 ..n3} , or {n1..n2 ..n3%fmt} , where * represents any character, l1,l2 are letters and n1,n2,n3 are signed numbers and fmt is a format specified as used by printf. In each case, fields are created by prepending the characters before the { and appending the characters after the } to each of the strings generated by the characters between the { and }. The resulting fields are checked to see if they have any brace patterns.

In the first form, a field is created for each string between { and ,, between , and ,, and between , and }. The string represented by * can contain embedded matching { and } without quoting. Otherwise, each { and } with * must be quoted.

In the seconds form, l1 and l2 must both be either upper case or both be lower case characters in the C locale. In this case a field is created for each character from l1 thru l2.

In the remaining forms, a field is created for each number starting at n1 and continuing until it reaches n2 incrementing n1 by n3. The cases where n3 is not specified behave as if n3 where 1 if n1<=n2 and −1 otherwise. If forms which specify %fmt any format flags, widths and precisions can be specified and fmt can end in any of the specifiers cdiouxX. For example, {a,z}{1..5..3%02d}{b..c}x expands to the 8 fields, a01bx, a01cx, a04bx, a04cx, z01bx, z01cx, z04bx and z4cx.

File Name Generation.

Following splitting, each field is scanned for the characters ∗, ?, (, and [ unless the −f option has been set. If one of these characters appears, then the word is regarded as a pattern. Each file name component that contains any pattern character is replaced with a lexicographically sorted set of names that matches the pattern from that directory. If no file name is found that matches the pattern, then that component of the filename is left unchanged unless the pattern is prefixed with ∼(N) in which case it is removed as described below. If FIGNORE is set, then each file name component that matches the pattern defined by the value of FIGNORE is ignored when generating the matching filenames. The names . and .. are also ignored. If FIGNORE is not set, the character . at the start of each file name component will be ignored unless the first character of the pattern corresponding to this component is the character . itself. Note, that for other uses of pattern matching the / and . are not treated specially.

∗

Matches any string, including the null string. When used for filename expansion, if the globstar option is on, two adjacent ∗’s by itself will match all files and zero or more directories and subdirectories. If followed by a / then only directories and subdirectories will match.

?

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.

Within [ and ], character classes can be specified with the syntax [:class:] where class is one of the following classes defined in the ANSI-C standard: (Note that word is equivalent to alnum plus the character _).

alnum alpha blank cntrl digit graph lower print punct space upper word xdigit
Within [ and ], an equivalence class can be specified with the syntax [=c=] which matches all characters with the same primary collation weight (as defined by the current locale) as the character c.
Within [ and ], [.symbol.] matches the collating symbol symbol.

A pattern-list is a list of one or more patterns separated from each other with a & or │. A & signifies that all patterns must be matched whereas │ requires that only one pattern be matched. Composite patterns can be formed with one or more of the following sub-patterns:

?(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.

{n}(pattern-list)

Matches n occurrences of the given patterns.

{m,n}(pattern-list)

Matches from m to n occurrences of the given patterns. If m is omitted, 0 will be used. If n is omitted at least m occurrences will be matched.

@(pattern-list)

Matches exactly one of the given patterns.

!(pattern-list)

Matches anything except one of the given patterns.

By default, each pattern, or sub-pattern will match the longest string possible consistent with generating the longest overall match. If more than one match is possible, the one starting closest to the beginning of the string will be chosen. However, for each of the above compound patterns a − can be inserted in front of the ( to cause the shortest match to the specified pattern-list to be used.

When pattern-list is contained within parentheses, the backslash character \ is treated specially even when inside a character class. All ANSI-C character escapes are recognized and match the specified character. In addition the following escape sequences are recognized:

\d

Matches any character in the digit class.

\D

Matches any character not in the digit class.

\s

Matches any character in the space class.

\S

Matches any character not in the space class.

\w

Matches any character in the word class.

\W

Matches any character not in the word class.

A pattern of the form %(pattern-pair(s)) is a sub-pattern that can be used to match nested character expressions. Each pattern-pair is a two character sequence which cannot contain & or │. The first pattern-pair specifies the starting and ending characters for the match. Each subsequent pattern-pair represents the beginning and ending characters of a nested group that will be skipped over when counting starting and ending character matches. The behavior is unspecified when the first character of a pattern-pair is alpha-numeric except for the following:

D

Causes the ending character to terminate the search for this pattern without finding a match.

E

Causes the ending character to be interpreted as an escape character.

L

Causes the ending character to be interpreted as a quote character causing all characters to be ignored when looking for a match.

Q

Causes the ending character to be interpreted as a quote character causing all characters other than any escape character to be ignored when looking for a match.

Thus, %({}Q"E\), matches characters starting at { until the matching } is found not counting any { or } that is inside a double quoted string or preceded by the escape character \. Without the {} this pattern matches any C language string.

Each sub-pattern in a composite pattern is numbered, starting at 1, by the location of the ( within the pattern. The sequence \n, where n is a single digit and \n comes after the n-th. sub-pattern, matches the same string as the sub-pattern itself.

Finally a pattern can contain sub-patterns of the form ∼(options:pattern-list), where either options or :pattern-list can be omitted. Unlike the other compound patterns, these sub-patterns are not counted in the numbered sub-patterns. If options is present, it can consist of one or more of the following:

+

Enable the following options. This is the default.

−

Disable the following options.

E

The remainder of the pattern uses extended regular expression syntax like the egrep(1) command.

F

The remainder of the pattern uses fgrep(1) expression syntax.

G

The remainder of the pattern uses basic regular expression syntax like the grep(1) command.

K

The remainder of the pattern uses shell pattern syntax. This is the default.

N

This is ignored. However, when it is the first letter and is used with file name generation, and no matches occur, the file pattern expands to the empty string.

i

Treat the match as case insensitive.

g

File the longest match (greedy). This is the default.

l

Left anchor the pattern. This is the default for K style patterns.

r

Right anchor the pattern. This is the default for K style patterns.

If both options and :pattern-list are specified, then the options apply only to pattern-list. Otherwise, these options remain in effect until they are disabled by a subsequent ∼(...) or at the end of the sub-pattern containing ∼(...).

Quoting.

Each of the metacharacters listed earlier (see Definitions above) has a special meaning to the shell and causes termination of a word unless quoted. A character may be quoted (i.e., made to stand for itself) by preceding it with a \. The pair \new-line is removed. All characters enclosed between a pair of single quote marks (′′) that is not preceded by a $ are quoted. A single quote cannot appear within the single quotes. A single quoted string preceded by an unquoted $ is processed as an ANSI-C string except for the following:

\0

Causes the remainder of the string to be ignored.

\E

Equivalent to the escape character (ascii 033),

\e

Equivalent to the escape character (ascii 033),

\cx

Expands to the character control-x.

\C[.name.]

Expands to the collating element name.

Inside double quote marks (""), parameter and command substitution occur and \ quotes the characters \, ` , ", and $. A $ in front of a double quoted string will be ignored in the "C" or "POSIX" locale, and may cause the string to be replaced by a locale specific string otherwise. The meaning of $∗ and $@ is identical when not quoted or when used as a variable assignment value or as a file name. However, when used as a command argument, "$∗" is equivalent to "$1d$2d...", where d is the first character of the IFS variable, whereas "$@" is equivalent to "$1" "$2" .... Inside grave quote marks ( `` ), \ quotes the characters \, ` , and $. If the grave quotes occur within double quotes, then \ also quotes the character ".

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 built-in command names listed below cannot be altered by quoting them.

Arithmetic Evaluation.

The shell performs arithmetic evaluation for arithmetic substitution, to evaluate an arithmetic command, to evaluate an indexed array subscript, and to evaluate arguments to the built-in commands shift and let. Evaluations are performed using double precision floating point arithmetic or long double precision floating point for systems that provide this data type. Floating point constants follow the ANSI-C programming language floating point conventions. Integer constants follow the ANSI-C programming language integer constant conventions although only single byte character constants are recognized and character casts are not recognized. In addition constants can be of the form [base#]n where base is a decimal number between two and sixty-four representing the arithmetic base and n is a number in that base. The digits above 9 are represented by the lower case letters, the upper case letters, @, and _ respectively. For bases less than or equal to 36, upper and lower case characters can be used interchangeably.

An arithmetic expression uses the same syntax, precedence, and associativity of expression as the C language. All the C language operators that apply to floating point quantities can be used. In addition, the operator ** can be used for exponentiation. It has higher precedence than multiplication and is left associative. In addition, when the value of an arithmetic variable or sub-expression can be represented as a long integer, all C language integer arithmetic operations can be performed. Variables can be referenced by name within an arithmetic expression without using the parameter expansion syntax. When a variable is referenced, its value is evaluated as an arithmetic expression.

Any of the following math library functions that are in the C math library can be used within an arithmetic expression:

abs acos acosh asin asinh atan atan2 atanh cbrt copysign cos cosh erf erfc exp exp2 expm1 fabs fdim finite floor fma fmax fmod hypot ilogb int isinf isnan j0 j1 jn lgamma log log2 logb nearbyint nextafter nexttoward pow remainder rint round sin sinh sqrt tan tanh tgamma trunc y0 y1 yn

An internal representation of a variable as a double precision floating point can be specified with the −E [n], −F [n], or −X [n] option of the typeset special built-in command. The −E option causes the expansion of the value to be represented using scientific notation when it is expanded. The optional option argument n defines the number of significant figures. The −F option causes the expansion to be represented as a floating decimal number when it is expanded. The −X option cause the expansion to be represented using the %a format defined by ISO C-99. The optional option argument n defines the number of places after the decimal (or radix) point in this case.

An internal integer representation of a variable can be specified with the −i [n] option of the typeset special built-in command. The optional option argument n specifies an arithmetic base to be used when expanding the variable. If you do not specify an arithmetic base, base 10 will be used.

Arithmetic evaluation is performed on the value of each assignment to a variable with the −E, −F, −X, or −i attribute. Assigning a floating point number to a variable whose type is an integer causes the fractional part to be truncated.

Prompting.

When used interactively, the shell prompts with the value of PS1 after expanding it for parameter expansion, command substitution, and arithmetic substitution, before reading a command. In addition, each single ! in the prompt is replaced by the command number. A !! is required to place ! in the prompt. If at any time a new-line is typed and further input is needed to complete a command, then the secondary prompt (i.e., the value of PS2 ) is issued.

Conditional Expressions.

A conditional expression is used with the [[ compound command to test attributes of files and to compare strings. Field splitting and file name generation are not performed on the words between [[ and ]]. Each expression can be constructed from one or more of the following unary or binary expressions:

string

True, if string is not null.

−a file

Same as −e below. This is obsolete.

−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 it has its setgid bit set.

−k file

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

−n string

True, if length of string is non-zero.

−o ?option

True, if option named option is a valid option name.

−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 it 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 true if 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.

−h file

True, if file exists and is a symbolic link.

−N file

True, if file exists and the modification time is greater than the last access time.

−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 file2 does not, or file1 is newer than file2.

file1 −ot file2

True, if file2 exists and file1 does not, or file1 is older than file2.

file1 −ef file2

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

string == pattern

True, if string matches pattern. Any part of pattern can be quoted to cause it to be matched as a string. With a successful match to a pattern, the .sh.match array variable will contain the match and sub-pattern matches.

string = pattern

Same as == above, but is obsolete.

string != pattern

True, if string does not match pattern. When the string matches the pattern the .sh.match array variable will contain the match and sub-pattern matches.

string =∼ ere

True if string matches the pattern ∼(E)ere where ere is an extended regular expression.

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.

The following obsolete arithmetic comparisons are also permitted:

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.

Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell. The following may appear anywhere in a simple-command or may precede or follow a command and are not passed on to the invoked command. Command substitution, parameter expansion, and arithmetic substitution occur before word or digit is used except as noted below. File name generation occurs only if the shell is interactive and the pattern matches a single file. Field splitting is not performed.

In each of the following redirections, if file is of the form /dev/sctp/host/port, /dev/tcp/host/port, or /dev/udp/host/port, where host is a hostname or host address, and port is a service given by name or an integer port number, then the redirection attempts to make a tcp, sctp or udp connection to the corresponding socket.

No intervening space is allowed between the characters of redirection operators.

<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

Write output to a temporary file. If the command completes successfully rename it to word, otherwise, delete the temporary file. >;word cannot be used with the exec(2). built-in.

>>word

Use file word as standard output. If the file exists, then output is appended to it (by first seeking to the end-of-file); otherwise, the file is created.

<>word

Open file word for reading and writing as standard output.

<>;word

The same as <>word except that if the command completes successfully, word is truncated to the offset at command completion. <>;word cannot be used with the exec(2). built-in.

<<[−]word

The shell input is read up to a line that is the same as word after any quoting has been removed, or to an end-of-file. No parameter substitution, command substitution, arithmetic 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 expansion, command substitution, and arithmetic substitution occur, \new-line is ignored, and \ must be used to quote the characters \, $, ` . If − is appended to <<, then all leading tabs are stripped from word and from the document. If # is appended to <<, then leading spaces and tabs will be stripped off the first line of the document and up to an equivalent indentation will be stripped from the remaining lines and from word. A tab stop is assumed to occur at every 8 columns for the purposes of determining the indentation.

<<<word

A short form of here document in which word becomes the contents of the here-document after any parameter expansion, command substitution, and arithmetic substitution occur.

<&digit

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

<&digit−

The file descriptor given by digit is moved to standard input. 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.

<#((expr))

Evaluate arithmetic expression expr and position file descriptor 0 to the resulting value bytes from the start of the file. The variables CUR and EOF evaluate to the current offset and end-of-file offset respectively when evaluating expr.

>#((offset))

The same as <# except applies to file descriptor 1.

<#pattern

Seeks forward to the beginning of the next line containing pattern.

<##pattern

The same as <# except that the portion of the file that is skipped is copied to standard output.

If one of the above is preceded by a digit, with no intervening space, then the file descriptor number referred to is that specified by the digit (instead of the default 0 or 1). If one of the above, other than >&− and the ># and <# forms, is preceded by {varname} with no intervening space, then a file descriptor number > 10 will be selected by the shell and stored in the variable varname. If >&− or the any of the ># and <# forms is preceded by {varname} the value of varname defines the file descriptor to close or position. For example:

... 2>&1

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

exec {n}<file

means open file named file for reading and store the file descriptor number in variable n.

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 (i.e. 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 (see environ(7)) is a list of name-value pairs that is passed to an executed program in the same way as a normal argument list. The names must be identifiers and the values are character strings. The shell interacts with the environment in several ways. On invocation, the shell scans the environment and creates a variable for each name found, giving it the corresponding value and attributes and marking it export. Executed commands inherit the environment. If the user modifies the values of these variables or creates new ones, using the export or typeset −x commands, they become part of the environment. The environment seen by any executed command is thus composed of any name-value pairs originally inherited by the shell, whose values may be modified by the current shell, plus any additions which must be noted in export or typeset −x commands.

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

(export TERM ; TERM =450; cmd args)

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

If the obsolete −k option 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 c
set −k
echo 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.

For historical reasons, there are two ways to define functions, the name() syntax and the function name syntax, described in the Commands section above. 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 defined by the function name syntax and called by name 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 in the environment of the caller after the function completes. Ordinarily, variables are shared between the calling program and the function. However, the typeset special built-in command used within a function defines local variables whose scope includes the current function. They can be passed to functions that they call in the variable assignment list that precedes the call or as arguments passed as name references. Errors within functions return control to the caller.

Functions defined with the name() syntax and functions defined with the function name syntax that are invoked with the . special built-in are executed in the caller’s environment and share all variables and traps with the caller. Errors within these function executions cause the script that contains them to abort.

The special built-in command return is used to return from function calls.

Function names can be listed with the −f or +f option of the typeset special built-in command. The text of functions, when available, will also be listed with −f. Functions can be undefined with the −f option of the unset special built-in command.

Ordinarily, functions are unset when the shell executes a shell script. Functions that need to be defined across separate invocations of the shell should be placed in a directory and the FPATH variable should contain the name of this directory. They may also be specified in the ENV file.

Discipline Functions.

Each variable can have zero or more discipline functions associated with it. The shell initially understands the discipline names get, set, append, and unset but can be added when defining new types. On most systems others can be added at run time via the C programming interface extension provided by the builtin built-in utility. If the get discipline is defined for a variable, it is invoked whenever the given variable is referenced. If the variable .sh.value is assigned a value inside the discipline function, the referenced variable will evaluate to this value instead. If the set discipline is defined for a variable, it is invoked whenever the given variable is assigned a value. If the append discipline is defined for a variable, it is invoked whenever a value is appended to the given variable. The variable .sh.value is given the value of the variable before invoking the discipline, and the variable will be assigned the value of .sh.value after the discipline completes. If .sh.value is unset inside the discipline, then that value is unchanged. If the unset discipline is defined for a variable, it is invoked whenever the given variable is unset. The variable will not be unset unless it is unset explicitly from within this discipline function.

The variable .sh.name contains the name of the variable for which the discipline function is called, .sh.subscript is the subscript of the variable, and .sh.value will contain the value being assigned inside the set discipline function. The variable _ is a reference to the variable including the subscript if any. For the set discipline, changing .sh.value will change the value that gets assigned. Finally, the expansion ${var.name}, when name is the name of a discipline, and there is no variable of this name, is equivalent to the command substitution ${ var.name;}.

Type Variables.

Typed variables provide a way to create data structure and objects. A type can be defined either by a shared library, by the enum built-in command described below, or by using the new −T option of the typeset built-in command. With the −T option of typeset, the type name, specified as an option argument to −T, is set with a compound variable assignment that defines the type. Function definitions can appear inside the compound variable assignment and these become discipline functions for this type and can be invoked or redefined by each instance of the type. The function name create is treated specially. It is invoked for each instance of the type that is created but is not inherited and cannot be redefined for each instance.

When a type is defined a special built-in command of that name is added. These built-ins are declaration commands and follow the same expansion rules as all the special built-in commands defined below that are preceded by ††. These commands can subsequently be used inside further type definitions. The man page for these commands can be generated by using the −−man option or any of the other −− options described with getopts. The −r, −a, −A, −h, and −S options of typeset are permitted with each of these new built-ins.

An instance of a type is created by invoking the type name followed by one or more instance names. Each instance of the type is initialized with a copy of the sub-variables except for sub-variables that are defined with the −S option. Variables defined with the −S are shared by all instances of the type. Each instance can change the value of any sub-variable and can also define new discipline functions of the same names as those defined by the type definition as well as any standard discipline names. No additional sub-variables can be defined for any instance.

When defining a type, if the value of a sub-variable is not set and the −r attribute is specified, it causes the sub-variable to be a required sub-variable. Whenever an instance of a type is created, all required sub-variables must be specified. These sub-variables become readonly in each instance.

When unset is invoked on a sub-variable within a type, and the −r attribute has not been specified for this field, the value is reset to the default value associative with the type. Invoking unset on a type instance not contained within another type deletes all sub-variables and the variable itself.

A type definition can be derived from another type definition by defining the first sub-variable name as _ and defining its type as the base type. Any remaining definitions will be additions and modifications that apply to the new type. If the new type name is the same is that of the base type, the type will be replaced and the original type will no longer be accessible.

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:

%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. The notify option of the set command causes the shell to print these job change messages as soon as they occur.

When the monitor option 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 immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated. When a login shell receives a HUP signal, it sends a HUP signal to each job that has not been disowned with the disown built-in command described below.

Signals.

The INT and QUIT signals for an invoked command are ignored if the command is followed by & and the monitor option is not active. Otherwise, signals have the values inherited by the shell from its parent (but see also the trap built-in command below).

Execution.

Each time a command is read, the above substitutions are carried out. If the command name matches one of the Special Built-in Commands listed below, it is executed within the current shell process. Next, the command name is checked to see if it matches a user defined function. If it does, the positional parameters are saved and then reset to the arguments of the function call. A function is also executed in the current shell process. When the function completes or issues a return, the positional parameter list is restored. For functions defined with the function name syntax, any trap set on EXIT within the function is executed. The exit value of a function is the value of the last command executed. If a command name is not a special built-in command or a user defined function, but it is one of the built-in commands listed below, it is executed in the current shell process.

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 equal to getconf PATH output. 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 of the given name that is not a directory. If found, and if the shell determines that there is a built-in version of a command corresponding to a given pathname, this built-in is invoked in the current process. If found, and this directory is also contained in the value of the FPATH variable, then this file is loaded into the current shell environment as if it were the argument to the . command except that only preset aliases are expanded, and a function of the given name is executed as described above. If not found, and the file .paths is found, and this file contains a line of the form FPATH=path where path names an existing directory, and this directory contains a file of the given name, then this file is loaded into the current shell environment as if it were the argument to the . special built-in command and a function of the given name is executed. Otherwise, if found, a process is created and an attempt is made to execute the command via exec(2).

When an executable is found, the directory where it is found in is searched for a file named .paths. If this file is found and it contains a line of the form BUILTIN_LIB=value , then the library named by value will be searched for as if it were an option argument to builtin -f, and if it contains a built-in of the specified name this will be executed instead of a command by this name. Otherwise, if this file is found and it contains a line of the form name=value in the first or second line, then the environment variable name is modified by prepending the directory specified by value to the directory list. If value is not an absolute directory, then it specifies a directory relative to the directory that the executable was found. If the environment variable name does not already exist it will be added to the environment list for the specified command.

If the file has execute permission but is not an a.out file, it is assumed to be a file containing shell commands. A separate shell is spawned to read it. All non-exported variables are removed in this case. If the shell command file doesn’t have read permission, or if the setuid and/or setgid bits are set on the file, then the shell executes an agent whose job it is to set up the permissions and execute the shell with the shell command file passed down as an open file. A parenthesized command is executed in a sub-shell without removing non-exported variables.

Command Re-entry.

The text of the last HISTSIZE (default 512) commands entered from a terminal device is saved in a history file. The file $HOME /.sh_history is used if the HISTFILE variable is not set or if the file it names is not writable. A shell can access the commands of all interactive shells which use the same named HISTFILE. The built-in command hist is used to list or edit a portion of this file. The portion of the file to be edited or listed can be selected by number or by giving the first character or characters of the command. A single command or range of commands can be specified. If you do not specify an editor program as an argument to hist then the value of the variable HISTEDIT is used. If HISTEDIT is unset, the obsolete variable FCEDIT is used. If FCEDIT is not defined, then /bin/ed is used. The edited command(s) is printed and re-executed upon leaving the editor unless you quit without writing. The −s option (and in obsolete versions, the editor name −) is used to skip the editing phase and to re-execute the command. In this case a substitution parameter of the form old=new can be used to modify the command before execution. For example, with the preset alias r, which is aliased to ′hist −s′, typing ‘r bad=good c’ will re-execute the most recent command which starts with the letter c, replacing the first occurrence of the string bad with the string good.

In-line Editing Options.

Normally, each command line entered from a terminal device is simply typed followed by a new-line (‘RETURN’ or ‘LINE FEED’). If either the emacs, gmacs, or vi option is active, the user can edit the command line. To be in either of these edit modes set the corresponding option. An editing option is automatically selected each time the VISUAL or EDITOR variable is assigned a value ending in either of these option names.

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.

Unless the multiline option is on, 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 (left, both) side(s) 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.

Each of the edit modes has an operation to list the files or commands that match a partially entered word. When applied to the first word on the line, or the first word after a ;, │, &, or (, and the word does not begin with ∼ or contain a /, the list of aliases, functions, and executable commands defined by the PATH variable that could match the partial word is displayed. Otherwise, the list of files that match the given word is displayed. If the partially entered word does not contain any file expansion characters, a * is appended before generating these lists. After displaying the generated list, the input line is redrawn. These operations are called command name listing and file name listing, respectively. There are additional operations, referred to as command name completion and file name completion, which compute the list of matching commands or files, but instead of printing the list, replace the current word with a complete or partial match. For file name completion, 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. Otherwise, the longest common prefix for all the matching files replaces the word. For command name completion, only the portion of the file names after the last / are used to find the longest command prefix. If only a single name matches this prefix, then the word is replaced with the command name followed by a space. When using a tab for completion that does not yield a unique match, a subsequent tab will provide a numbered list of matching alternatives. A specific selection can be made by entering the selection number followed by a tab.

Key Bindings.

The KEYBD trap can be used to intercept keys as they are typed and change the characters that are actually seen by the shell. This trap is executed after each character (or sequence of characters when the first character is ESC) is entered while reading from a terminal. The variable .sh.edchar contains the character or character sequence which generated the trap. Changing the value of .sh.edchar in the trap action causes the shell to behave as if the new value were entered from the keyboard rather than the original value.

The variable .sh.edcol is set to the input column number of the cursor at the time of the input. The variable .sh.edmode is set to ESC when in vi insert mode (see below) and is null otherwise. By prepending ${.sh.editmode} to a value assigned to .sh.edchar it will cause the shell to change to control mode if it is not already in this mode.

This trap is not invoked for characters entered as arguments to editing directives, or while reading input for a character search.

Emacs Editing Mode.

This mode is entered by enabling either the emacs or gmacs option. The only difference between these two modes is the way they handle ^T. To edit, the user moves the cursor to the point needing correction and then inserts or deletes characters or words as needed. All the editing commands are control characters or escape sequences. The notation for control characters is caret (^) followed by the character. For example, ^F is the notation for control F. This is entered by depressing ‘f’ while holding down the ‘CTRL’ (control) key. The ‘SHIFT’ key is not depressed. (The notation ^? indicates the DEL (delete) key.)

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 ‘LINE FEED’ key is entered after edit commands except when noted.

^F

Move cursor forward (right) one character.

M-[C

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-[D

Move cursor backward (left) one character.

M-b

Move cursor backward one word.

^A

Move cursor to start of line.

M-[H

Move cursor to start of line.

^E

Move cursor to end of line.

M-[Y

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.

lnext

(User defined literal next character as defined by the stty(1) command, or ^V if not defined.) Removes the next character’s editing features (if any).

^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 previous character and advance the cursor 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 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.

M-^L

Clear the screen.

^@

(Null character) Set mark.

M-space

(Meta space) Set mark.