ksh(1) ksh(1)
NAME
ksh, rksh, pfksh - KornShell, a standard/restricted command and pro-
gramming language
NOTE
Currently, rksh and pfksh are not available on Mac OS X / Darwin.
SYNOPSIS
[ +-abcefhikmnoprstuvxBCDP ] [ -R file ] [ +-o option ] ... [ - ] [ arg
... ]
rksh [ +-abcefhikmnoprstuvxBCD ] [ -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 /
than 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 parenthesis, 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 as 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. With 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 the 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 the 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 exe-
cuted. 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
VISUAL or EDITOR variable is assigned a value ending in either of these
option names.
The editing features require that the user's terminal accept `RETURN'
as carriage return without line feed and that a space (` ') must 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-<