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ksh(1) ksh(1)
NAME
ksh - Korn shell
SYNOPSIS
ksh [-ir] [-c command_string | -s] [+ | -abCefhkmnopstuvx] [+ | -o][option
...]
| [+ | -A name] [argument ...] | [file] [argument ...]
The Korn shell is an interactive command interpreter and a command program-
ming language.
DESCRIPTION
The Korn shell carries out commands either interactively from a terminal
keyboard or from a file. The Korn shell is backward compatible with the
Bourne shell (invoked with the sh command) and contains virtually all of
the Bourne shell features, as well as several of the best features of the C
shell.
Some important features of the Korn shell are as follows:
++ Command aliasing
++ Filename substitution
++ Tilde substitution
++ Command substitution
++ Parameter substitution
++ Job control
++ Inline editing
A
script, a shell procedure, or a command file.
A simple command is a sequence of words separated by spaces or tabs. A
word is a sequence of characters that contains no unquoted spaces or tabs.
The first word in the sequence (numbered as 0), usually specifies the name
of a command. Any remaining words, with a few exceptions, are passed to
that command. A space refers to both spaces and tabs.
The value of a simple command is its exit value if it ends normally, or
(octal) 200 added to the signal number if it terminates due to a signal.
For a list of status values, see the signal() system call.
A pipeline is a sequence of one or more commands separated by a | (vertical
bar) or, for historical compatibility, by a ^ (circumflex). In a pipeline,
the standard output of each command becomes the standard input of the next
command. Each command runs as a separate process, and the shell waits for
the last command to end. A filter is a command that reads its standard
input, transforms it in some way, then writes it to its standard output. A
pipeline normally consists of a series of filters. Although the processes
in a pipeline (except the first process) can execute in parallel, they are
synchronized to the extent that each program needs to read the output of
its predecessor.
The exit value of a pipeline is the exit value of the last command.
A list is a sequence of one or more pipelines separated by ; (semicolon), &
(ampersand), && (two ampersands), or || (two vertical bars) and optionally
ended by a ; (semicolon), an & (ampersand), a |& (coprocess), or a newline.
These separators and terminators have the following effects:
; Causes sequential execution of the preceding pipeline; the shell waits
for the pipeline to finish.
& Causes asynchronous execution of the preceding pipeline; the shell does
not wait for the pipeline to finish.
&& Causes the list following it to be executed only if the preceding pipe-
line returns a 0 (zero) exit value.
|| Causes the list following it to be executed only if the preceding pipe-
line returns a nonzero exit value.
The cd command is an exception; if it returns a nonzero exit value, no
subsequent commands in a list are executed, regardless of the separator
characters.
The ; and & separators have equal precedence, as do && and ||. The
single-character separators have lower precedence than the double-character
separators. An unquoted newline character following a pipeline functions
the same as a ; (semicolon).
Comments
The shell treats as a comment any word that begins with a # character and
ignores that word and all characters following up to the next newline char-
acter.
Shell Flow Control Statements
Unless otherwise stated, the value returned by a command is that of the
last simple command executed in the command.
for identifier [in word...] ;do list ;done
Each time a for command is executed, identifier is set to the next word
taken from the in word list. If in word ... is omitted, the for com-
mand executes the do list once for each positional parameter that is
set. (See Parameter Substitution.) Execution ends when there are no
more words in the list.
select identifier [in word...] ;do list ;done
Prints on standard error (file descriptor 2), the set of words, each
preceded by a number. If in word... is omitted, then the positional
parameters are used instead. (See Parameter Substitution.) The PS3
prompt is printed and a line is read from the standard input. If this
line consists of the number of one of the listed words, then the value
of the parameter identifier is set to the word corresponding to this
number. If this line is empty, the selection list is printed again.
Otherwise, the value of the parameter identifier is set to null. The
contents of the line read from standard input is saved in the REPLY
parameter. The list is executed for each selection until a break or
End-of-File is encountered.
case word in [[(] pattern [| pattern] ...) list ;;] ... esac
Executes the list associated with the first pattern that matches word.
The form of the patterns is the same as that used for filename genera-
tion. (See Filename Generation.)
if list ;then list [elif list ;then list] ... [;else list] ;fi
Executes the list following if and, if it returns a 0 (zero) exit
status, executes the list following the first then. Otherwise, the
list following elif is executed and, if its value is 0 (zero), the list
following the next then is executed. Failing that, the else list is
executed. If no else list or then list is executed, then the if com-
mand returns a 0 (zero) exit status.
while list ;do list ;done
until list ;do list ;done
Executes the while list repeatedly, and if the exit status of the last
command in the list is 0 (zero), executes the do list; otherwise the
loop terminates. If no commands in the do list are executed, then the
while command returns a 0 (zero) exit status; until can be used in
place of while to negate the loop termination test.
(list)
Executes list in a separate environment. Note that if two adjacent
open parentheses are needed for nesting, a space must be inserted to
avoid arithmetic evaluation as described later.
{list;}
Executes list. Note that unlike the metacharacters ( and ), { and }
are reserved words and must be at the beginning of a line or after a ;
(semicolon) in order to be recognized.
[[expression]]
is TRUE. See Conditional Expressions for a description of expression.
function identifier {list;}
identifier. The body of the
function is the list of commands between { and }. (See Functions.)
time pipeline
Executes pipeline and prints the elapsed time as well as the user and
system time on standard error.
The following reserved words are recognized only when they appear, without
single or double quotes, as the first word of a command:
if for case
then while esac
else until function
elif do select
fi done time
{ } [[ ]]
Command Aliasing
The first word of each command is replaced by the text of an alias (if an
alias for this word was defined). The first character of an alias name can
be any nonspecial printable character, but the rest of the characters must
be the same as for a valid identifier. The replacement string can contain
any valid shell script, including the metacharacters previously listed.
The first word of each command in the replaced text, other than any that
are in the process of being replaced, is tested for aliases. If the last
character of the alias value is a space, the word following the alias will
also be checked for alias substitution.
Aliases can be used to redefine special built-in commands but cannot be
used to redefine the reserved words previously listed. Aliases can be
created, listed, and exported with the alias command and can be removed
with the unalias command. Exported aliases remain in effect for scripts
invoked by name, but must be reinitialized for separate invocations of the
shell. (See Invocation.)
Aliasing is performed when scripts are read, not while they are executed.
Therefore, for an alias to take effect, the alias definition command has to
be executed before the command that references the alias is read.
Aliases are frequently used as shorthand for full pathnames. An option to
the aliasing facility allows the value of the alias to be automatically set
to the full pathname of the corresponding command. These aliases are
called tracked aliases.
The value of a tracked alias is defined the first time the corresponding
command is looked up and becomes undefined each time the PATH environment
variable is reset. These aliases remain tracked so that the next subse-
quent reference will redefine the value. Several tracked aliases are com-
piled into the shell. The -h flag of the set command makes each referenced
command name into a tracked alias.
The following exported aliases are compiled into the shell, but can be
unset or redefined:
autoload='typeset -fu'
false='let 0'
functions='typeset -f'
hash='alias -t'
history='fc -l'
integer='typeset -i'
nohup='nohup '
r='fc -e -'
true=':'
type='whence -v'
Tilde Substitution
After alias substitution is performed, each word is checked to see if it
begins with an unquoted ~ (tilde). If it does, then the word up to a /
(slash) is checked to see if it matches a username in the /etc/passwd file.
If a match is found, the tilde and the matched login name are replaced by
the login directory of the matched user. This is called a tilde substitu-
tion. If no match is found, the original text is left unchanged. A tilde
by itself, or in front of a /, is replaced by the value of the HOME parame-
ter. A tilde followed by a + (plus sign) or - (dash) is replaced by $PWD
and $OLDPWD, respectively.
In addition, tilde substitution is attempted when the value of a variable
assignment parameter begins with a tilde.
Command Substitution
The standard output from a command enclosed in parentheses preceded by a
dollar sign $( ) or a pair of `` (grave accents) can be used as part or all
of a word; trailing newlines are removed. In the second (archaic) form,
the string between the grave accents is processed for special quoting char-
acters before the command is executed. (See Quoting.) The command substi-
tution $(cat file) can be replaced by the equivalent but faster $(<file).
Command substitution of most special commands that do not perform
input/output redirection are carried out without creating a separate pro-
cess. An arithmetic expression enclosed in double parentheses preceded by
a dollar sign ( $(( )) ) is replaced by the value of the arithmetic expres-
sion within the double parentheses.
Parameter Substitution
A parameter is an identifier, one or more digits, or any of the characters
*, @, #, ?, -, $, and !. A named parameter (a parameter denoted by an
identifier) has a value and 0 (zero) or more attributes. Named parameters
can be assigned values and attributes by using the typeset special command.
The attributes supported by the shell are described later with the typeset
special command. Exported parameters pass values and attributes to the
environment.
The shell supports a 1-dimensional array facility. An element of an array
parameter is referenced by a subscript. A subscript is denoted by an
arithmetic expression enclosed with [ ] (brackets). To assign values to an
array, use set -A name value ... The value of all subscripts must be in
the range of 0 to 1023. Arrays need not be declared. Any reference to a
named parameter with a valid subscript is legal and an array is created if
necessary. Referencing an array without a subscript is equivalent to
referencing the element 0 (zero).
The value of a named parameter can be assigned by the following:
name=value [ name=value ]
If the integer attribute, -i, is set for name, the value is subject to
arithmetic evaluation, as described later. Positional parameters, which
are denoted by a number, can be assigned values with the set special com-
mand. Parameter $0 is set from argument 0 (zero) when the shell is
invoked. The $ (dollar sign) character is used to introduce substitutable
parameters.
${parameter}
Reads all the characters from the ${ (dollar sign left brace) to the
matching } (right brace) as part of the same word even if it contains
braces or metacharacters. The value, if any, of the parameter is sub-
stituted. 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 or when a named parameter is subscripted. If parameter is one
or more digits, it is a positional parameter. A positional parameter
of more than one digit must be enclosed in braces. If parameter is *
(asterisk) or @ (at sign), all the positional parameters, starting with
$1, are substituted (separated by a field separator character). If an
array identifier with subscript * or @ is used, the value for each of
the elements is substituted (separated by a field separator character).
${#parameter}
Substitutes the number of positional parameters if parameter is * or @;
otherwise, the length of the value of the parameter is substituted.
${#identifier[*]}
Substitutes the number of elements in the array identifier.
${parameter:-word}
Substitutes the value of parameter if it is set and non-null; other-
wise, substitute word.
${parameter:=word}
Sets parameter to word if it is not set or is null; the value of the
parameter is then substituted. Positional parameters cannot be
assigned values in this way.
${parameter:?[word]}
Substitutes the value of parameter if it is set and is non-null; other-
wise, print word and exit from the shell. If word is omitted, a stan-
dard message is printed.
${parameter:+word}
Substitute word if parameter is set and is non-null; otherwise, substi-
tute nothing.
${parameter#pattern} | ${parameter##pattern}
Causes the value of this substitution to be the value of parameter with
the matched portion deleted if the shell pattern matches the beginning
of the value of parameter; otherwise the value of parameter is substi-
tuted. In the first form, the smallest matching pattern is deleted and
in the second form, the largest matching pattern is deleted.
${parameter%pattern} | ${parameter%%pattern}
Causes the value of this substitution to be the value of parameter with
the matched part deleted if the shell pattern matches the end of the
value of parameter; 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.
If the : (colon) is omitted from the previous expressions, then the shell
checks only whether parameter is set or not.
In the previous expressions, word is not evaluated unless it is to be used
as the substituted string, so that, in the following example, pwd is exe-
cuted only if d is not set or is null:
echo ${d:-$(pwd)}
The following parameters are automatically set by the shell:
# (hash mark)
The number of positional parameters in decimal.
- (dash)
Flags supplied to the shell on invocation or by the set command.
? (question mark)
The decimal value returned by the last executed command.
$ (dollar sign)
The process number of this shell.
MAIL file when checking
for mail.
! (exclamation point)
The process number of the last background command invoked.
ERRNO
The value of errno as set by the most recently failed system call.
This value is system dependent and is intended for debugging purposes.
LINENO
The line number of the current line within the script or function being
executed.
OLDPWD
The previous working directory set by the cd command.
OPTARG
The value of the last option argument processed by the getopts special
command.
OPTIND
The index of the last option argument processed by the getopts special
command.
PPID
The process number of the parent of the shell.
PWD The present working directory set by the cd command.
RANDOM
Each time this parameter 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 parameter is set by the select statement and by the read special
command when no arguments are supplied.
SECONDS
Each time this parameter is referenced, the number of seconds since
shell invocation is returned. If this parameter is assigned a value,
then the value returned upon reference is the value that was assigned
plus the number of seconds since the assignment.
The following parameters 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 value of this variable ends in emacs, gmacs, or vi and the
VISUAL variable is not set, then the corresponding option (see set
under Special ksh Commands) is turned on.
ENV If this parameter is set, then parameter substitution is performed on
the value to generate the pathname of the script that is executed when
the shell is invoked. (See Invocation.) This file is typically used
for alias and function definitions.
FCEDIT
The default editor name for the fc command.
FPATH
The search path for function definitions. This path is searched when a
function with the -u attribute is referenced and when a command is not
found. If an executable file is found, then it is read and executed in
the current environment.
IFS Internal field separators, normally spaces, tabs, and newlines that are
used to separate command words which result from command or parameter
substitution and for separating words with the read special command.
The first character of the IFS parameter is used to separate arguments
for the $* substitution. (See Quoting.)
HISTFILE
If this parameter is set when the shell is invoked, then the value is
the pathname of the file that is used to store the command history.
(See Command Reentry.)
HISTSIZE
If this parameter is set when the shell is invoked, the number of
previously entered commands that are accessible by this shell is
greater than or equal to this number. The default is 128.
HOME
The default argument (home directory) for the cd command.
LANG
Specifies the locale of your system, which is comprised of three parts:
language, territory, and codeset. The default locale is the C locale,
which specifies the value English for language, U.S. for territory, and
ASCII for codeset. The locale specified for the LANG variable controls
the language applied to messages. Unless set explicitly, the
LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, and LC_TIME
variables also derive their settings from the locale set for LANG.
LC_COLLATE
Specifies the collating sequence to use when sorting names and when
character ranges occur in patterns. The default value is the collating
sequence for American English. If absent, the collating sequence can
be taken from the LANG parameter. If both LC_COLLATE and LANG are
absent, the ANSI C collating sequence is used.
LC_CTYPE
Specifies the character classification information to use on your sys-
tem. The default value is American English.
LC_MESSAGES
Specifies the language that the system expects for user input of yes
and no strings. The default value is American English.
LC_MONETARY
Specifies the monetary format for your system. The default value is
the monetary format for American English.
LC_NUMERIC
Specifies the numeric format for your system. The default value is the
numeric format for American English.
LC_TIME
Specifies the date and time format for your system. The default value
is the date and time format for American English.
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.
LOGNAME
The name of the user's login account corresponding to the login name in
the user database.
MAIL
If this parameter is set to the name of a mail file and the MAILPATH
parameter is not set, the shell informs you of the arrival of mail in
the specified file.
MAILCHECK
This variable specifies how often (in seconds) the shell checks for
changes in the modification time of any of the files specified by the
MAILPATH or MAIL parameters. The default value is 600 seconds. When
the time has elapsed, the shell checks before issuing the next prompt.
MAILPATH
A list of filenames separated by : (colons). If this parameter is set,
the shell informs you of any modifications to the specified files that
have occurred within the last MAILCHECK seconds. Each filename can be
followed by a ? (question mark) and a message that is printed. The
message will undergo parameter substitution with the parameter, $_
defined as the name of the file that has changed. The default message
is you have mail in $_.
NLSPATH
Specifies a list of directories to search to find message catalogs.
PATH
The search path for commands. (See Execution.) You cannot change PATH
if executing under rsh, except in .profile.
PS1 The value of this parameter is expanded for parameter substitution to
define the primary prompt string which by default is the $ (dollar
sign). The ! (exclamation point) in the primary prompt string is
replaced by the command number. (See Command Reentry.)
PS2 Secondary prompt string, by default > (right angle bracket).
PS3 Selection prompt string used within a select loop, by default #?
(number sign, question mark).
PS4 The value of this parameter is expanded for parameter substitution and
precedes each line of an execution trace. If omitted, the execution
trace prompt is + (plus sign).
SHELL
The pathname of the shell is kept in the environment.
TMOUT
If set to a value greater than 0 (zero), the shell terminates if a com-
mand is not entered within the prescribed number of seconds after issu-
ing the PS1 prompt. (Note that the shell can be compiled with a max-
imum bound for this value that cannot be exceeded.)
VISUAL
If the value of this variable ends in emacs, gmacs, or vi, the
corresponding option (see the set command in Special ksh Commands) is
turned on.
The shell gives default values to PATH, PS1, PS2, MAILCHECK, TMOUT, and
IFS, while HOME, SHELL, ENV, and MAIL are not set by the shell (although
HOME is set by the login command). On some systems, MAIL and SHELL are
also set by the login command.
Interpretation of Spaces
After parameter and command substitution, the results of substitutions are
scanned for the field separator characters (those found in IFS), and split
into distinct arguments where such characters are found. Explicit null
arguments (`` or '') are retained. Implicit null arguments (those result-
ing from parameters that have no values) are removed.
Filename Generation
Following substitution, each command word is scanned for the characters *
(asterisk), ? (question mark), and [ ] (brackets), unless the -f option was
set. If one of these characters appears, the word is regarded as a pat-
tern. The word is replaced with lexicographically sorted filenames that
match the pattern. If no filename is found that matches the pattern, the
word is left unchanged. When a pattern is used for filename generation,
the . (dot) character at the start of a filename or immediately following a
/ (slash), as well as the / character itself, must be matched explicitly.
In other instances of pattern matching, the / and . are not treated spe-
cially.
* Matches any string, including the null string.
? Matches any single character.
[...]
Matches any one of the enclosed characters. In an expression such as
[a-z], the - (dash) means "through" according to the current collating
sequence. The collating sequence is determined by the value of the
LC_COLLATE environment variable. If the first character following the
[ (left bracket) is a ! (exclamation point), then any character not
enclosed is matched. A - can be included in the character set by put-
ting it as the first or last character.
A pattern_list is a list of one or more patterns separated from each other
with a | (vertical bar). Composite patterns can be formed with one or more
of the following:
?(pattern_list)
Optionally matches any one of the given patterns.
*(pattern_list)
Matches zero or more occurrences of the given patterns.
+(pattern_list)
Matches one or more occurrences of the given patterns.
@(pattern_list)
Matches exactly one of the given patterns.
!(pattern_list)
Matches anything, except one of the given patterns.
Character Classes
You can use the following notation to match filenames within a range indi-
cation:
[:charclass:]
This format instructs the system to match any single character belonging to
charclass; the defined classes correspond to ctype() subroutines as fol-
lows:
alnum
alpha
cntrl
digit
graph
lower
print
punct
space
upper
xdigit
Your locale might define additional character properties, such as the fol-
lowing:
[:vowel:]
The preceding character class could be TRUE for a, e, i, o, u, or y. You
could then use [:vowel] inside a set construction to match any vowel.
Refer to The LC_CTYPE Category section of the locale file format reference
page for more information.
Quoting
The following characters have a special meaning to the shell and cause ter-
mination of a word unless quoted:
; & ( ) | ^ < > Ctrl-x>
Interchanges the cursor and mark.
Erase
Deletes the previous character. (User-defined Erase character as
defined by the stty command, often space>
Sets the mark.
> or _>, ,
.
_>
Same as the