KSH(1)KSH(1)NAME
ksh, rksh, pfksh - KornShell, a standard/restricted command and pro‐
gramming language
SYNOPSIS
[ ±abcefhiknoprstuvxBCDP ] [ -R file ] [ ±o option ] ... [ - ] [ arg
... ]
DESCRIPTION
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 envi‐
ronments whose capabilities are more controlled than those of the stan‐
dard shell. Rpfksh is a profile shell version of the command inter‐
preter ksh; it is used to to execute commands with the attributes spec‐
ified 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. Identi‐
fiers 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 lan‐
guage. 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 rea‐
sons, 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 possi‐
bly 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 com‐
mand 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 sym‐
bol ⎪& 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 semi‐
colon, 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 occuring within a while, until, or if list, can be prededed 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 posi‐
tional 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 Arith‐
metic 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 eval‐
uated. 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 pat‐
tern 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. Other‐
wise, 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 eval‐
uation described below. If the value of the arithmetic expres‐
sion is non-zero, the exit status is 0, otherwise the exit sta‐
tus is 1.
(list)
Execute list in a separate environment. Note, that if two adja‐
cent 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 begin‐
ning of a line or after a ; in order to be recognized.
[[ expression ]]
Evaluates expression and returns a zero exit status when expres‐
sion is true. See Conditional Expressions below, for a descrip‐
tion 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 var‐
name() 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 spec‐
ifies 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, export, or readonly special built-in com‐
mands. 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 var‐
name. 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.
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.
Comments.
A word beginning with # causes that word and all the following charac‐
ters 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 exe‐
cuted. 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 ′
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 origi‐
nal 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 enclosed in parentheses preceded by
a dollar sign ( $() ) or a pair of grave accents (``) may be used as
part or all of a word; trailing new-lines are removed. In the second
(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.
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 asyn‐
chronously 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.
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 set -A vname value ... . The value of all subscripts must
be in the range of 0 through 1,048,575. 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 sub‐
script 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 con‐
tains 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 ref‐
erence 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 ref‐
erences and assignments to the variable whose name has been passed to
the function.
If either of the floating point attributes, -E, or -F, or the integer
attribute, -i, is set for vname, then the value is subject to arith‐
metic 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 metacharac‐
ters. 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 parame‐
ter. A positional parameter of more than one digit must be
enclosed in braces. If parameter is ∗ or @, then all the posi‐
tional parameters, starting with $1, are substituted (separated
by a field separator character). If an array vname with sub‐
script ∗ or @ is used, then the value for each of the elements
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 parame‐
ter is substituted.
${#vname[*]}
${#vname[@]}
The number of elements in the array vname is substituted.
${!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 @.
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.
${!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 parame‐
ters 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 interac‐
tive). If word is omitted then a standard message is printed.
${parameter:+word}
If parameter is set and is non-null then substitute word; other‐
wise substitute nothing.
In the above, word is not evaluated unless it is to be used as the sub‐
stituted 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 nega‐
tive 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 ele‐
ments 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 small‐
est 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 sub‐
script @ or *, the substring operation is applied to each ele‐
ment 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 pat‐
tern 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 por‐
tion 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 environ‐
ment. Subsequently it is assigned the last argument of
the previous command. This parameter is not set for com‐
mands 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
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 charac‐
ter (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 pro‐
cessing a KEYBD trap.
.sh.file
The pathname of the file than contains the current com‐
mand.
.sh.fun
The name of the current function that is being executed.
.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 oper‐
ators #, %, 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 disci‐
pline 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.
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 sec‐
onds since shell invocation is returned. If this vari‐
able 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.
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, com‐
mand substitution, and arithmetic substitution are per‐
formed on the value to generate the pathname of the
script that will be executed when the shell is invoked
(see Invocation below). This file is typically used for
alias and function definitions. The default value is
$HOME/.kshrc.
FCEDIT Obsolete name for the default editor name for the hist
command. FCEDIT is not used when HISTEDIT is set.
FIGNORE
A pattern that defines the set of filenames that will be
ignored when performing filename matching.
FPATH The search path for function definitions. The directo‐
ries in this path are searched for a file with the same
name as the function or command when a function with the
-u attribute is referenced and when a command is not
found. If an executable file with the name of that com‐
mand is found, then it is read and executed in the cur‐
rent environment. Unlike PATH, the current directory
must be represented explictily by . rather than by adja‐
cent : characters or a beginning or ending :.
HISTCMD
Number of the current command in the history file.
HISTEDIT
Name for the default editor name for the hist command.
HISTFILE
If this variable is set when the shell is invoked, then
the value is the pathname of the file that will be used
to store the command history (see Command Re-entry
below).
HISTSIZE
If this variable is set when the shell is invoked, then
the number of previously entered commands that are acces‐
sible by this shell will be greater than or equal to this
number. The default is 512.
HOME The default argument (home directory) for the cd command.
IFS Internal field separators, normally space, tab, and new-
line that are used to separate the results of command
substitution or parameter expansion and to separate
fields with the built-in command read. The first charac‐
ter of the IFS variable is used to separate arguments for
the "$∗" 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 adja‐
cent 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.
LANG This variable determines the locale category for any cat‐
egory 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 charac‐
ter collation information.
LC_CTYPE
This variable determines the locale category for charac‐
ter 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 dec‐
imal 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 substi‐
tution, and arithmetic substitution with the variable $_
defined as the name of the file that has changed. The
default message is you have mail in $_.
PATH The search path for commands (see Execution below). The
user may not change PATH if executing under rksh (except
in .profile).
PS1 The value of this variable is expanded for parameter
expansion, command substitution, and arithmetic substitu‐
tion to define the primary prompt string which by default
is ``$''. 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 substi‐
tution 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 pre‐
fixed 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 for‐
mat 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 braces 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 speci‐
fied, 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.)
VISUAL 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 sub‐
stitutions 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 substi‐
tutions 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 let‐
ters 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 pat‐
terns.
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 cre‐
ated 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 oth‐
erwise. If forms which specify %fmt any format flags, widths and pre‐
cisions 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 compo‐
nent that contains any pattern character is replaced with a lexico‐
graphically 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 fol‐
lowing the opening [ is a ! then any character not
enclosed is matched. A - can be included in the charac‐
ter 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 char‐
acter 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 pat‐
terns 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 char‐
acter \ is treated specially even when inside a character class. All
ANSI-C character escapes are recognized and match the specified charac‐
ter. 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 sub‐
sequent 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 look‐
ing 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:pat‐
tern-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 expres‐
sion 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-pat‐
tern containing ∼(...).
Quoting.
Each of the metacharacters listed earlier (see Definitions above) has a
special meaning to the shell
i Treat the match as case insensitive.
g File the longest match (greedy). This is the default.
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-pat‐
tern 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 other‐
wise. 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 charac‐
ters \, `, 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 func‐
tion 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 sub‐
script, 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 char‐
acter 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 associa‐
tivity 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 vari‐
able 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 lgamma log log2 logb nearbyint nextafter nexttoward pow
remainder rint round sin sinh sqrt tan tanh tgamma trunc
An internal representation of a variable as a double precision floating
point can be specified with the -E [n] or -F [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 fig‐
ures. The -F option causes the expansion to be represented as a float‐
ing decimal number when it is expanded. The optional option argument n
defines the number of places after the decimal 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, 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 arith‐
metic 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 fur‐
ther 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 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 input.
<<[-]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 per‐
formed 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 substitu‐
tion 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 docu‐
ment and up to an equivalent indentation will be stripped
from the remaining lines and from word. A tab stop is
assumend 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 expan‐
sion, 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 contain‐
ing 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 interven‐
ing 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 assign‐
ment 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 built-in commands listed below - those that are pre‐
ceded 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 ver‐
sions 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 exe‐
cuted like commands with the arguments passed as positional parameters.
(See Execution below.)
Functions defined by the function name syntax and called by name exe‐
cute 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 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 ref‐
erenced variable will evaluate to this value instead. If the set dis‐
cipline 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. For the set discipline, changing
.sh.value will change the value that gets assigned.
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 num‐
bers. 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.
This paragraph and the next require features that are not in all ver‐
sions of UNIX and may not apply. If you are running a job and wish to
do something else you may hit the key ^Z (control-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 out‐
put 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 pro‐
duce 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 nor‐
mally 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 trig‐
gers 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 com‐
mand 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 com‐
mand 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 com‐
mand 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 con‐
taining 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 direc‐
tory 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 direc‐
tory 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 con‐
tains 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 prepend‐
ing 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 vari‐
able 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 exe‐
cutes 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 writ‐
ing. 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 VIS‐
UAL 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 over‐
write the current character on the screen.
Unless the multiline option is on, the editing modes implement a con‐
cept 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 con‐
tain 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 direc‐
tory. 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 exam‐
ple, ^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) com‐
mand, 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 ter‐
minals).
^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.
^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-[A Equivalent to ^P.
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.
M-[B Equivalent to ^N.
^Rstring Reverse search history for a previous command line containing
string. If a parameter of zero is given, the search is for‐
ward. 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-=, 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. This can be used
to program function 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-* Attempt file name generation on the current word. An aster‐
isk is appended if the word doesn't match any file or contain
any special pattern characters.
M-ESC Command or file name completion as described above.
^I tab Attempts command or file name completion as described above.
If a partial completion occurs, repeating this will behave as
if M-= were entered. If no match is found or entered after
space, a tab is inserted.
M-= If not preceded by a numeric parameter, it generates the list
of matching commands or file names as described above. Oth‐
erwise, the word under the cursor is replaced by the item
corresponding to the value of the numeric parameter from the
most recently generated command or file list. If the cursor
is not on a word, it is inserted instead.
^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).
M-^V Display version of the shell.
M-# If the line does not begin with a #, a # is inserted at the
beginning of the line and after each new-line, and the line
is entered. This causes a comment to be inserted in the his‐
tory file. If the line begins with a #, the # is deleted and
one # after each new-line is also deleted.
Vi Editing Mode.
There are two typing modes. Initially, when you enter a command you
are in the input mode. To edit, the user enters control mode by typing
ESC (033) and moves the cursor to the point needing correction and then
inserts or deletes characters or words as needed. Most control com‐
mands accept an optional repeat count prior to the command.
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 sec‐
ond has elapsed since the prompt was printed. The ESC character termi‐
nates 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 canoni‐
cal 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
By default the editor is in input mode.
erase (User defined erase character as defined by the stty
command, usually ^H or #.) Delete previous character.
^W Delete the previous blank separated word. On some
systems the viraw option may be required for this to
work.
eof As the first character of the line causes the shell to
terminate unless the ignoreeof option is set. Other‐
wise this character is ignored.
lnext (User defined literal next character as defined by the
stty(1) or ^V if not defined.) Removes the next char‐
acter's editing features (if any). On some systems
the viraw option may be required for this to work.
\ Escape the next erase or kill character.
^I tab Attempts command or file name completion as described
above and returns to input mode. If a partial comple‐
tion occurs, repeating this will behave as if = were
entered from control mode. If no match is found or
entered after space, a tab is inserted.
Motion Edit Commands
These commands will move the cursor.
[count]l Cursor forward (right) one character.
[count][C 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][D 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.
0 Cursor to start of line.
^ Cursor to start of line.
[H Cursor to first non-blank character in line.
$ Cursor to end of line.
[Y 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
These commands access your command history.
[count]k Fetch previous command. Each time k is entered the
previous command back in time is accessed.
[count]- Equivalent to k.
[count][A 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][B 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 `NEW LINE'. 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.
Text Modification Edit Commands
These commands will modify the line.
a Enter input mode and enter text after the current
character.
A Append text to the end of the line. Equivalent to $a.
[count]cmotion
c[count]motion
Delete current character through the character that
motion would move the cursor to and enter input mode.
If motion is c, the entire line will be deleted and
input mode entered.
C Delete the current character through the end of line
and enter input mode. Equivalent to c$.
S Equivalent to cc.
[count]s Replace characters under the cursor in input mode.
D Delete the current character through the end of line.
Equivalent to d$.
[count]dmotion
d[count]motion
Delete current character through the character that
motion would move to. If motion is d , the entire
line will be deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line. Equiva‐
lent to 0i.
[count]P Place the previous text modification before the cur‐
sor.
[count]p Place the previous text modification after the cursor.
R Enter input mode and replace characters on the screen
with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the current
cursor position with c, and advance the cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]∼ Invert the case of the count character(s) starting at
the current cursor position and advance the cursor.
[count]_ Causes the count word of the previous command to be
appended and input mode entered. The last word is
used if count is omitted.
* Causes an * to be appended to the current word and
file name generation attempted. If no match is found,
it rings the bell. Otherwise, the word is replaced by
the matching pattern and input mode is entered.
\ Command or file name completion as described above.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that motion
would move the cursor to and puts them into the delete
buffer. The text and cursor are unchanged.
yy Yanks the entire line.
Y Yanks from current position to end of line. Equiva‐
lent to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands performed on the
line.
[count]v Returns the command hist -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 uncommenting previously commented
commands in the history file.
[count]= If count is not specified, it generates the list of
matching commands or file names as described above.
Otherwise, the word under the the cursor is replaced
by the count item from the most recently generated
command or file list. If the cursor is not on a word,
it is inserted instead.
@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 process‐
ing.
^V Display version of the shell.
Built-in Commands.
The following simple-commands are executed in the shell process.
Input/Output redirection is permitted. Unless otherwise indicated, the
output is written on file descriptor 1 and the exit status, when there
is no syntax error, is zero. Except for :, true, false, echo, newgrp,
and login, all built-in commands accept -- to indicate end of options.
They also interpret the option --man as a request to display the man
page onto standard error and -? as a help request which prints a usage
message on standard error. Commands that are preceded by one or two †
symbols are special built-in commands and are treated specially in the
following ways:
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. They are not valid function names.
5. 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 per‐
formed after the = sign and field splitting and file name gener‐
ation are not performed.
† : [ arg ... ]
The command only expands parameters.
† . name [ arg ... ]
If name is a function defined with the function name reserved
word syntax, the function is executed in the current environment
(as if it had been defined with the name() syntax.) Otherwise
if name refers to a file, the file is read in its entirety and
the commands are executed in the current shell environment. The
search path specified by PATH is used to find the directory con‐
taining the file. If any arguments arg are given, they become
the positional parameters while processing the . command and
the original positional parameters are restored upon completion.
Otherwise the positional parameters are unchanged. The exit
status is the exit status of the last command executed.
†† alias [ -ptx ] [ name[ =value ] ] ...
alias with no arguments prints the list of aliases in the form
name=value on standard output. The -p option causes the word
alias to be inserted before each one. When one or more argu‐
ments are given, 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 obsolete -t option 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 alias
remains tracked. Without the -t option, for each name in the
argument list for which no value is given, the name and value of
the alias is printed. The obsolete -x option has no effect.
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 for a
description of the format of job.
† break [ n ]
Exit from the enclosing for, while, until, or select loop, if
any. If n is specified, then break n levels.
builtin [ -ds ] [ -f file ] [ name ... ]
If name is not specified, and no -f option is specified, the
built-ins are printed on standard output. The -s option prints
only the special built-ins. Otherwise, each name represents the
pathname whose basename is the name of the built-in. The entry
point function name is determined by prepending b_ to the built-
in name. The ISO C/C++ prototype is b_mycommand(int argc, char
*argv[], void *context) for the builtin command mycommand where
argv is array an of argc elements and context is an optional
pointer to a Shell_t structure as described in <ast/shell.h>.
Special built-ins cannot be bound to a pathname or deleted. The
-d option deletes each of the given built-ins. On systems that
support dynamic loading, the -f option names a shared library
containing the code for built-ins. The shared library prefix
and/or suffix, which depend on the system, can be omitted. Once
a library is loaded, its symbols become available for subsequent
invocations of builtin. Multiple libraries can be specified
with separate invocations of the builtin command. Libraries are
searched in the reverse order in which they are specified. When
a library is loaded, it looks for a function in the library
whose name is lib_init() and invokes this function with an argu‐
ment of 0.
cd [ -LP ] [ arg ]
cd [ -LP ] 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 direc‐
tory 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> (spec‐
ifying 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.
By default, symbolic link names are treated literally when find‐
ing the directory name. This is equivalent to the -L option.
The -P option causes symbolic links to be resolved when deter‐
mining the directory. The last instance of -L or -P on the com‐
mand line determines which method is used.
The cd command may not be executed by rksh. rksh93.
command [ -pvxV ] name [ arg ... ]
Without the -v or -V options, command executes name with the
arguments given by arg. The -p option causes a default path to
be searched rather than the one defined by the value of PATH.
Functions will not be searched for when finding name. In addi‐
tion, if name refers to a special built-in, none of the special
properties associated with the leading daggers will be honored.
(For example, the predefined alias redirect=′command exec′ pre‐
vents a script from terminating when an invalid redirection is
given.) With the -x option, if command execution would result
in a failure because there are too many arguments, errno E2BIG,
the shell will invoke command name multiple times with a subset
of the arguments on each invocation. Arguments that occur prior
to the first word that expands to multiple arguments and after
the last word that expands to multiple arguments will be passed
on each invocation. The exit status will be the maximum invoca‐
tion exit status. With the -v option, command is equivalent to
the built-in whence command described below. The -V option
causes command to act like whence -v.
† continue [ n ]
Resume the next iteration of the enclosing for, while, until, or
select loop. If n is specified, then resume at the n-th enclos‐
ing loop.
disown [ job... ]
Causes the shell not to send a HUP signal to each given job, or
all active jobs if job is omitted, when a login shell termi‐
nates.
echo [ arg ... ]
When the first arg does not begin with a -, and none of the
arguments contain a \, then echo prints each of its arguments
separated by a space and terminated by a new-line. Otherwise,
the behavior of echo is system dependent and print or printf
described below should be used. See echo(1) for usage and
description.
† eval [ arg ... ]
The arguments are read as input to the shell and the resulting
command(s) executed.
† exec [ -c ] [ -a name ] [ arg ... ]
If arg is given, the command specified by the arguments is exe‐
cuted in place of this shell without creating a new process.
The -c option causes the environment to be cleared before apply‐
ing variable assignments associated with the exec invocation.
The -a option causes name rather than the first arg, to become
argv[0] for the new process. Input/output arguments may appear
and affect the current process. If arg is not 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 shell 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. An end-of-file will also cause the shell
to exit except for a shell which has the ignoreeof option (see
set below) turned on.
†† export [ -p ] [ name[=value] ] ...
If name is not given, the names and values of each variable with
the export attribute are printed with the values quoted in a
manner that allows them to be re-input. The -p option causes
the word export to be inserted before each one. Otherwise, the
given names are marked for automatic export to the environment
of subsequently-executed commands.
false Does nothing, and exits 1. Used with until for infinite loops.
fg [ job... ]
This command is only on systems that support job control. Each
job specified is brought to the foreground and waited for in the
specified order. Otherwise, the current job is brought into the
foreground. See Jobs for a description of the format of job.
getconf [ name [ pathname ] ]
Prints the current value of the configuration parameter given by
name. The configuration parameters are defined by the IEEE
POSIX 1003.1 and IEEE POSIX 1003.2 standards. (See pathconf(2)
and sysconf(2).) The pathname argument is required for parame‐
ters whose value depends on the location in the file system. If
no arguments are given, getconf prints the names and values of
the current configuration parameters. The pathname / is used
for each of the parameters that requires pathname.
getopts [ -a name ] optstring vname [ 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. Options beginning with + are only recognized when opt‐
string begins with a +. 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. The option -? causes getopts to
generate a usage message on standard error. The -a argument can
be used to specify the name to use for the usage message, which
defaults to $0.
getopts places the next option letter it finds inside variable
vname each time it is invoked. The option letter will be
prepended with a + 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 vname to ? for an
unknown option and to : when a required option argument is miss‐
ing. Otherwise, getopts prints an error message. The exit sta‐
tus is non-zero when there are no more options.
There is no way to specify any of the options :, +, -, ?, [, and
]. The option # can only be specified as the first option.
hist [ -e ename ] [ -nlr ] [ first [ last ] ]
hist -s [ 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 num‐
ber is used as an offset to the current command number. If the
-l option is selected, the commands are listed on standard out‐
put. 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 HISTEDIT is used. If HISTEDIT is
not set, then FCEDIT (default /bin/ed) is used as the editor.
When editing is complete, the edited command(s) is executed if
the changes have been saved. 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
option -r reverses the order of the commands and the option -n
suppresses command numbers when listing. In the second form,
command is interpreted as first described above and defaults to
the last command executed. The resulting command is executed
after the optional substitution old=new is performed.
jobs [ -lnp ] [ job ... ]
Lists information about each given job; or all active jobs if
job is omitted. The -l option lists process ids in addition to
the normal information. The -n option only displays jobs that
have stopped or exited since last notified. The -p option
causes only the process group to be listed. See Jobs for a
description of the format of job.
kill [ -s signame ] job ...
kill [ -n signum ] job ...
kill -l [ sig ... ]
Sends either the TERM (terminate) signal or the specified signal
to the specified jobs or processes. Signals are either given by
number with the -n option or by name with the -s option (as
given in <signal.h>, stripped of the prefix ``SIG'' with the
exception that SIGCLD is named CHLD). For backward compatibil‐
ity, the n and s can be omitted and the number or name placed
immediately after the -. If the signal being sent is TERM (ter‐
minate) 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 third form, kill -l, if sig is not specified, the
signal names are listed. Otherwise, for each sig that is a
name, the corresponding signal number is listed. For each sig
that is a number, the signal name corresponding to the least
significant 8 bits of sig is listed.
let arg ...
Each arg is a separate arithmetic expression to be evaluated.
See Arithmetic Evaluation 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.
† newgrp [ arg ... ]
Equivalent to exec /bin/newgrp arg ....
print [ -Renprs ] [ -u unit] [ -f format ] [ arg ... ]
With no options or with option - or --, each arg is printed on
standard output. The -f option causes the arguments to be
printed as described by printf. In this case, any e, n, r, R
options are ignored. Otherwise, unless the -R or -r, are speci‐
fied, the following escape conventions will be applied:
\a The alert character (ascii 07).
\b The backspace character (ascii 010).
\c Causes print to end without processing more arguments and
not adding a new-line.
\f The formfeed character (ascii 014).
\n The new-line character (ascii 012).
\r The carriage return character (ascii 015).
\t The tab character (ascii 011).
\v The vertical tab character (ascii 013).
\E The escape character (ascii 033).
\\ The backslash character \.
\0x The character defined by the 1, 2, or 3-digit octal
string given by x.
The -R option will print all subsequent arguments and options
other than -n. The -e causes the above escape conventions to be
applied. This is the default behavior. It reverses the effect
of an earlier -r. The -p option causes the arguments to be
written onto the pipe of the process spawned with ⎪& instead of
standard output. The -s option causes the arguments to be writ‐
ten onto the history file instead of standard output. The -u
option can be used to specify a one digit file descriptor unit
number unit on which the output will be placed. The default is
1. If the option -n is used, no new-line is added to the out‐
put.
printf format [ arg ... ]
The arguments arg are printed on standard output in accordance
with the ANSI-C formatting rules associated with the format
string format. If the number of arguments exceeds the number of
format specifications, the format string is reused to format
remaining arguments. The following extensions can also be used:
A %b format can be used instead of %s to cause escape sequences
in the corresponding arg to be expanded as described in print.
A %B option causes each of the arguments to be treated as vari‐
able names and the binary value of variable will be printed.
This is most useful for variables whose attribute is -b. A %H
format can be used instead of %s to cause characters in arg that
are special in HTML and XML to be output as their entity name.
A %P format can be used instead of %s to cause arg to be inter‐
preted as an extended regular expression and be printed as a
shell pattern. A %R format can be used instead of %s to cause
arg to be interpreted as a shell pattern and to be printed as an
extended regular expression. A %q format can be used instead of
%s to cause the resulting string to be quoted in a manner than
can be reinput to the shell. A %(date-format)T format can be
use to treat an argument as a date/time string and to format the
date/time according to the date-format as defined for the
date(1) command. A %Z format will output a byte whose value is
0. The precision field of the %d format can be followed by a .
and the output base. In this case, the # flag character caues
base# to be prepended. The # flag when used with the d speci‐
fier without an output base, causes the output to be displayed
in thousands units with one of the suffixes k M G T P E to indi‐
cate the unit. The # flag when used with the i specifier causes
the output to be displayed in 1024 with one of the suffixes Ki
Mi Gi Ti Pi Ei to indicate the unit. The = flag has been added
to center the output within the specified field width.
pwd [ -LP ]
Outputs the value of the current working directory. The -L
option is the default; it prints the logical name of the current
directory. If the -P option is given, all symbolic links are
resolved from the name. The last instance of -L or -P on the
command line determines which method is used.
read [ -Aprs ] [ -d delim] [ -n n] [ [ -N n] [ [ -t timeout] [ -u unit]
[ vname?prompt ] [ vname ... ]
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. The -d option
causes the read to continue to the first character of delim
rather than new-line. The -n option causes at most n bytes to
read rather a full line but will return when reading from a slow
device as soon as any characters have been read. The -N option
causes exactly n to be read unless an end-of-file has been
encountered or the read times out because of the -t option. In
raw mode, -r, the \ character is not treated specially. The
first field is assigned to the first vname, the second field to
the second vname, etc., with leftover fields assigned to the
last vname. When vname has the binary attribute and -n or -N is
specified, the bytes that are read are stored directly into the
variable. If the -v is specified, then the value of the first
vname will be used as a default value when reading from a termi‐
nal device. The -A option causes the variable vname to be unset
and each field that is read to be stored in successive elements
of the indexed array vname. 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 option is present, the input will be
saved as a command in the history file. The option -u can be
used to specify a one digit file descriptor unit unit to read
from. The file descriptor can be opened with the exec special
built-in command. The default value of unit n is 0. The option
-t is used to specify a timeout in seconds when reading from a
terminal or pipe. If vname is omitted, then REPLY is used as
the default vname. An end-of-file 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 end-of-file is encountered or
read has timed out.
†† readonly [ -p ] [ vname[=value] ] ...
If vname is not given, the names and values of each variable
with the readonly attribute is printed with the values quoted in
a manner that allows them to be re-inputted. The -p option
causes the word readonly to be inserted before each one. Other‐
wise, the given vnames are marked readonly and these names can‐
not be changed by subsequent assignment.
† return [ n ]
Causes a shell function or . script to return to the invoking
script 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 return status is that of the last command exe‐
cuted. If return is invoked while not in a function or a .
script, then it behaves the same as exit.
† set [ ±CGabefhkmnoprstuvx ] [ ±o [ option ] ] ... [ ±A vname ] [ arg
... ]
The options for this command have meaning as follows:
-A Array assignment. Unset the variable vname and assign
values sequentially from the arg list. If +A is used,
the variable vname is not unset first.
-B Enable brace pattern field generation. This is the
default behavior.
-C Prevents redirection > from truncating existing files.
Files that are created are opened with the O_EXCL mode.
Requires >⎪ to truncate a file when turned on.
-G Causes the pattern ∗∗ by itself to match files and zero
or more directories and sub-directories when used for
file name generation. If followed by a / only directo‐
ries and sub-directories are matched.
-a All subsequent variables that are defined are automati‐
cally exported.
-b Prints job completion messages as soon as a background
job changes state rather than waiting for the next
prompt.
-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 encoun‐
tered.
-k (Obsolete). 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 option is turned on auto‐
matically 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.
bracexpand
Same as -B.
emacs Puts you in an emacs style in-line editor for
command entry.
globstar
Same as -G.
gmacs Puts you in a gmacs style in-line editor for
command entry.
ignoreeof
The shell will not exit on end-of-file. 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.
multiline
The built-in editors will use multiple lines on
the screen for lines that are longer than the
width of the screen. This may not work for all
terminals.
noclobber
Same as -C.
noexec Same as -n.
noglob Same as -f.
nolog Do not save function definitions in the history
file.
notify Same as -b.
nounset Same as -u.
pipefail
A pipeline will not complete until all compo‐
nents of the pipeline have completed, and the
return value will be the value of the last non-
zero command to fail or zero if no command has
failed.
showme When enabled, simple commands or pipelines pre‐
ceded by a semicolon (;) will be displayed as if
the xtrace option were enabled but will not be
executed. Otherwise, the leading ; will be
ignored.
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 the 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 (gid) is not
equal to the real uid (gid). Turning this off causes
the effective uid and gid to be set to the real uid and
gid.
-r Enables the restricted shell. This option cannot be
unset once set.
-s Sort the positional parameters lexicographically.
-t (Obsolete). Exit after reading and executing one com‐
mand.
-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.
-- Do not change any of the options; useful in setting $1
to a value beginning with -. If no arguments follow
this option then the positional parameters are unset.
As an obsolete feature, if the first arg is - then the -x and -v
options are turned off and the next arg is treated as the first
argument. Using + rather than - causes these options to be
turned off. These options can also be used upon invocation of
the shell. The current set of options 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 ... are renamed $1 ... ,
default n is 1. The parameter n can be any arithmetic expres‐
sion that evaluates to a non-negative number less than or equal
to $#.
sleep seconds
Suspends execution for the number of decimal seconds or frac‐
tions of a second given by seconds.
† trap [ -p ] [ action ] [ sig ] ...
The -p option causes the trap action associated with each trap
as specified by the arguments to be printed with appropriate
quoting. Otherwise, action will be processed as if it were an
argument to eval when the shell receives signal(s) sig. Each
sig can be given as a number or as the name of the signal. Trap
commands are executed in order of signal number. Any attempt to
set a trap on a signal that was ignored on entry to the current
shell is ineffective. If action is omitted and the first sig is
a number, or if action is -, then the trap(s) for each sig are
reset to their original values. If action is the null string
then this signal is ignored by the shell and by the commands it
invokes. If sig is ERR then action will be executed whenever a
command has a non-zero exit status. If sig is DEBUG then action
will be executed before each command. The variable .sh.command
will contain the contents of the current command line when
action is running. If sig is 0 or EXIT and the trap statement
is executed inside the body of a function defined with the func‐
tion name syntax, then the command action is executed after the
function completes. If sig is 0 or EXIT for a trap set outside
any function then the command action is executed on exit from
the shell. If sig is KEYBD, then action will be executed when‐
ever a key is read while in emacs, gmacs, or vi mode. The trap
command with no arguments prints a list of commands associated
with each signal number.
true Does nothing, and exits 0. Used with while for infinite loops.
†† typeset [ ±AHflabnprtux ] [ ±EFLRZi[n] ] [ vname[=value ] ] ...
Sets attributes and values for shell variables and functions.
When invoked inside a function defined with the function name
syntax, a new instance of the variable vname is created, and the
variable's value and type are restored when the function com‐
pletes. The following list of attributes may be specified:
-A Declares vname to be an associative array. Subscripts
are strings rather than arithmetic expressions.
-a Declares vname to be an indexed array. This is optional
unless except for compound variable assignments.
-E Declares vname to be a double precision floating point
number. If n is non-zero, it defines the number of sig‐
nificant figures that are used when expanding vname.
Otherwise, ten significant figures will be used.
-F Declares vname to be a double precision floating point
number. If n is non-zero, it defines the number of
places after the decimal point that are used when expand‐
ing vname. Otherwise ten places after the decimal point
will be used.
-H This option 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 neces‐
sary, to fit into the field. The -R option 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 option is
turned off.
-Z Right justify and fill with leading zeros if the first
non-blank character is a digit and the -L option has not
been set. Remove leading zeros if the -L option is also
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 options are -t, -u and -x. The -t option turns on
execution tracing for this function. The -u option
causes this function to be marked undefined. The FPATH
variable will be searched to find the function definition
when the function is referenced. If no options other
than -f is specified, then the function definition will
be displayed on standard output. If +f is specified,
then a line containing the function name followed by a
shell comment containing the line number and path name of
the file where this function was defined, if any, is dis‐
played.
-b The variable can hold any number of bytes of data. The
data can be text or binary. The value is represented by
the base64 encoding of the data. If -Z is also speci‐
fied, the size in bytes of the data in the buffer will be
determined by the size associated with the -Z. If the
base64 string assigned results in more data, it will be
truncated. Otherwise, it will be filled with bytes whose
value is zero. The printf format %B can be used to out‐
put the actual data in this buffer instead of the base64
encoding of the data.
-i Declares vname to be represented internally as integer.
The right hand side of an assignment is evaluated as an
arithmetic expression when assigning to an integer. If n
is non-zero, it defines the output arithmetic base, oth‐
erwise the output base will be ten.
-l All upper-case characters are converted to lower-case.
The upper-case option, -u, is turned off.
-n Declares vname to be a reference to the variable whose
name is defined by the value of variable vname. This is
usually used to reference a variable inside a function
whose name has been passed as an argument.
-r The given vnames are marked readonly and these names can‐
not 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.
The lower-case option, -l, is turned off.
-x The given vnames are marked for automatic export to the
environment of subsequently-executed commands. Variables
whose names contain a . cannot be exported.
The -i attribute cannot be specified along with -R, -L, -Z, or
-f.
Using + rather than - causes these options to be turned off. If
no vname arguments are given, a list of vnames (and optionally
the values) of the variables is printed. (Using + rather than -
keeps the values from being printed.) The -p option causes
typeset followed by the option letters to be printed before each
name rather than the names of the options. If any option other
than -p is given, only those variables which have all of the
given options are printed. Otherwise, the vnames and attributes
of all variables that have attributes are printed.
ulimit [ -HSacdfmnpstv ] [ limit ]
Set or display a resource limit. The available resource limits
are listed below. Many systems do not support 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 options 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 nor S option 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 than 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 that can be writ‐
ten by the current process or by child processes (files
of any size may be read).
-m The number of K-bytes on the size of physical memory.
-n The number of file descriptors plus 1.
-p The number of 512-byte blocks for pipe buffering.
-s The number of K-bytes on the size of the stack area.
-t The number of CPU 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 comple‐
ment of the previous umask value. If mask is omitted, the cur‐
rent value of the mask is printed. The -S option causes the
mode to be printed as a symbolic value. Otherwise, the mask is
printed in octal.
† unalias [ -a ] name ...
The aliases given by the list of names are removed from the
alias list. The -a option causes all the aliases to be unset.
†unset [ -fnv ] vname ...
The variables given by the list of vnames are unassigned, i.e.,
their values and attributes are erased. Readonly variables can‐
not be unset. If the -f option is set, then the names refer to
function names. If the -v option is set, then the names refer
to variable names. The -f option overrides -v. If -n is set
and name is a name reference, then name will be unset rather
than the variable that it references. The default is equivalent
to -v. Unsetting 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 last process waited for if job is specified; otherwise it is
zero. See Jobs for a description of the format of job.
whence [ -afpv ] name ...
For each name, indicate how it would be interpreted if used as a
command name.
The -v option produces a more verbose report. The -f option
skips the search for functions. The -p option does a path
search for name even if name is an alias, a function, or a
reserved word. The -p option turns off the -v option. The -a
option is similar to the -v option but causes all interpreta‐
tions of the given name to be reported.
Invocation.
If the shell is invoked by exec(2), and the first character of argument
zero ($0) is -, then the shell is assumed to be a login shell and com‐
mands are read from /etc/profile and then from either .profile in the
current directory or $HOME/.profile, if either file exists. Next, for
interactive shells, commands are read from the file named by performing
parameter expansion, command substitution, and arithmetic substitution
on the value of the environment variable ENV if the file exists. If
the -s option is not present and arg and a file by the name of arg
exists, then it reads and executes this script. Otherwise, if the
first arg does not contain a /, a path search is performed on the first
arg to determine the name of the script to execute. The script arg
must have execute permission and any setuid and setgid settings will be
ignored. If the script is not found on the path, arg is processed as
if it named a built-in command or function. Commands are then read as
described below; the following options are interpreted by the shell
when it is invoked:
-c If the -c option is present, then commands are read from the
first arg. Any remaining arguments become positional parame‐
ters starting at 0.
-s If the -s option 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 option is present or if the shell input and output
are attached to a terminal (as told by tcgetattr(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 option is present, the shell is a restricted shell.
-D A list of all double quoted strings that are preceded by a $
will be printed on standard output and the shell will exit.
This set of strings will be subject to language translation
when the locale is not C or POSIX. No commands will be exe‐
cuted.
-P If -P or -o profile is present, the shell is a profile shell
(see pfexec(1)).
-R filename
The -R filename option is used to generate a cross reference
database that can be used by a separate utility to find defi‐
nitions and references for variables and commands. The file‐
name argument specifies the generated database. A script file
must be provided on the command line as well.
The remaining options and arguments are described under the set command
above. An optional - as the first argument is ignored.
Rksh Only.
Rksh is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell. The
actions of rksh are identical to those of ksh, except that the follow‐
ing are disallowed:
Unsetting the restricted option.
changing directory (see cd(1)),
setting or unsetting the value or attributes of SHELL, ENV,
FPATH, or PATH,
specifying path or command names containing /,
redirecting output (>, >|, <>, and >>).
adding or deleting built-in commands.
using command -p to invoke a command.
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 stan‐
dard 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 (e.g.,
/usr/rbin) that can be safely invoked by rksh.
EXIT STATUS
Errors detected by the shell, such as syntax errors, cause the shell to
return a non-zero exit status. If the shell is being used non-interac‐
tively, then execution of the shell file is abandoned unless the error
occurs inside a subshell in which case the subshell is abandoned. Oth‐
erwise, the shell returns the exit status of the last command executed
(see also the exit command above). Run time errors detected by the
shell are reported by printing the command or function name and the
error condition. If the line number that the error occurred on is
greater than one, then the line number is also printed in square brack‐
ets ([]) after the command or function name.
FILES
/etc/profile The system wide initialization file, executed for login
shells.
$HOME/.profile
The personal initialization file, executed for login shells
after /etc/profile.
$HOME/..kshrc
Default personal initialization file, executed for interactive
shells when ENV is not set.
/etc/suid_profile
Alternative initialization file, executed when instead of per‐
sonal initialization file when the real and effective user or
group id do not match.
/dev/null
NULL device
SEE ALSOcat(1), cd(1), chmod(1), cut(1), egrep(1), echo(1), emacs(1), env(1),
fgrep(1), gmacs(1), grep(1), newgrp(1), pfexec(1), stty(1), test(1),
umask(1), vi(1), dup(2), exec(2), fork(2), getpwnam(3), ioctl(2),
lseek(2), paste(1), pathconf(2), pipe(2), sysconf(2), umask(2),
ulimit(2), wait(2), rand(3), a.out(5), profile(5), environ(7).
Morris I. Bolsky and David G. Korn, The New KornShell Command and Pro‐
gramming Language, Prentice Hall, 1995.
POSIX - Part 2: Shell and Utilities, IEEE Std 1003.2-1992, ISO/IEC
9945-2, IEEE, 1993.
CAVEATS
If a command 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 char‐
acter ⎪.
Using the hist 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 commands defined in the file.
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.
It is a good idea to leave a space after the comma operator in arith‐
metic expressions to prevent the comma from being interpreted as the
decimal point character in certain locales.
RDS Standard User Environment Utilities KSH(1)
