Korn Shell

On this page:

Invocation Options
Built-in Commands and Keywords
Built-in Shell Variables
set -o Options
Basic Korn Shell Operators
Substitutions
Regular Expression Operators
Double Operators
String Comparison Operators
Test Operators
Arithmetic and Relational Operators
Typeset Options
External links:
Korn Shell Programming Tutorial
Kornshell.com
More Comprehensive Lists and Examples

Option	Meaning
Invocation Options Back to top Table of Contents.
These options can be used when invoking the Korn shell. In addition, any set option can be used on the command-line. Login shells are usually invoked with the options -i (interactive), -s (read from standard input), and -m (enable job control).
-c string	Execute string, then exit.
-s	Read commands from the standard input. If an argument is given, this flag takes precedence (i.e., the argument won't be treated as a script name and standard input will be read).
-i	Interactive shell. Ignore signals TERM, INTR, and QUIT.
-r	Restricted shell.

Built-in Commands and Keywords
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Command	Meaning	Command	Meaning
:	Do nothing (just do expansions of arguments).	let	Arithmetic variable assignment.
.	Read file and execute its contents in current shell.	newgrp	Start new shell with new group ID.
alias	Set up shorthand for command or command-line	print	Expand and print arguments on standard output.
bg	Put job in background.	pwd	Print working directory.
break	Exit from surrounding for, select, while, or until loop.	read	Read a line from standard input.
case	Multi-way conditional construct.	readonly	Make variables read-only (unassignable).
cd	Change working directory.	return	Return from surrounding function or script.
continue	Skip to next iteration of for, select, while, or until loop.	select	Menu generation construct.
echo	Expand and print arguments.	set	Set options.
exec	Replace shell with given program.	shift	Shift command-line arguments.
exit	Exit from shell.	time	Run command and print execution times.
export	Create environment variables.	trap	Set up signal-catching routine.
eval	Process arguments as a command line.	typeset	Set special characteristics of variables.
fc	Fix command (edit history file).	ulimit	Set/show process resource limits.
fg	Put background job in foreground.	umask	Set/show file permission mask.
for	Looping construct.	unalias	Remove alias definitions.
function	Define function.	unset	Remove definitions of variables or functions.
getopts	Process command-line options.	until	Looping construct.
if	Conditional construct.	wait	Wait for background job(s) to finish.
jobs	List background jobs.	whence	Identify source of command.
kill	Send signal to process.	while	Looping construct.

Variable	Meaning	Default	Set by:
Built-in Shell Variables Back to top Table of Contents.
#	Number of arguments given to current process.
-	Options given to shell on invocation.	See above.
?	Exit status of previous command.	none	ksh
$	Process ID of shell process.	none	ksh
_	Last argument to previous command.	none	ksh
!	Process ID of last background command.	none	ksh
CDPATH	List of directories for cd command to search.	none	User
COLUMNS	Width of display in columns (for editing modes and select).	80	System Administrator
EDITOR	Used to set editing mode; also used by mail and other programs.	/bin/ed	User, System Administrator
ERRNO	Error number of last system call that failed.	none	ksh
ENV	Name of file to run as environment file when shell is invoked.	none	User, System Administrator
FCEDIT	Default editor for fc command.	/bin/ed	User, System Administrator
FPATH	Search path for autoloaded functions.	none	User
HISTFILE	Name of command history file.	$HOME/.sh_history	User, System Administrator
HISTSIZE	Number of lines kept in history file.	128	User, System Administrator
HOME	Home (login) directory.	none	System Administrator
IFS	Internal field separator; list of characters that act as word separators.	SPACE, TAB, and NEWLINE.	User
LINENO	Number of line in script or function that just ran.	none	ksh
LINES	Height of display in line (for select command).	24	System Administrator
LOGNAME	User name.	none	System Administrator
MAIL	Name of file to check for new mail.	none	System Administrator
MAILCHECK	How often (in seconds) to check for new mail.	600 seconds	User, System Administrator
MAILPATH	List of file names to check for new mail, if MAIL is not set.	none	System Administrator
OLDPWD	Previous working directory.	none	ksh
OPTARG	Option to argument being processed by getopts.	none	ksh
OPTIND	Number of first argument after options.	none	ksh
PATH	Search path for commands.	/bin:/usr/bin	User, System Administrator
PPID	Process ID of parent process.	none	ksh
PS1	Primary command prompt string.	$	User
PS2	Prompt string for line continuations.	>	User
PS3	Prompt string for select command.	#?	User
PS4	Prompt string for xtrace option.	+	User
PWD	Current working directory.	none	User
RANDOM	Random number between 0 and 32767 (2¹⁵ - 1)	none	ksh
REPLY	User's response to select command; result of read command if no variable names given.	none	System Administrator
SECONDS	Number of seconds since shell was invoked.	none	ksh
SHELL	Full pathname of shell.	none	System Administrator
TERM	Type of terminal user is utilizing.	none	System Administrator
TMOUT	If set to positive integer, number of seconds between commands after which shell automatically terminates.	0 (unlimited)	ksh
VISUAL	Used to set editing mode.	/bin/ed	User, System Administrator

set -o Options
Back to top Table of Contents.

these are options that can be turned on with the set -o command. All are initially off except where noted. Abbrevs, where listed, are arguments to set that can be used instead of the full set -o command (e.g., set -a is an abbreviation for set -o allexport). the abbreviations are actually backward-compatible Bourne shell options.

Option

Abbreviation

Meaning

allexport

-a

Export all subsequently defined variables.

errexit

-e

Exit the shell when a command exits with a non-0 status.

bgnice

Run all background jobs at decreased priority (on by default).

emacs

Use emacs-style command-line editing.

gmacs

Use emacs-style command-line editing, but with a slightly different meaning for CTRL-T.

ignoreeof

Disallow CTRL-D to exit the shell.

markdirs

Add / to all directory names generated from wildcard expansion.

monitor

-m

Enable job control (on by default).

noclobber

Don't allow > redirection to existing files.

noexec

-n

Read commands and check for syntax errors, but don't execute them.

noglob

-f

Disable wildcard expansion.

nolog

Disable command history.

nounset

-u

Treat undefined variables as errors, not as null.

privileged

-p

Script is running in suid mode.

trackall

-h

Substitute full pathnames for commands in alias expansions.

verbose

-v

Print commands (verbatim) before running them.

Use vi-style command-line editing.

viraw

Use vi mode and have each keystroke take effect immediately.

xtrace

-x

Print commands (after expansions) before running them.

Basic Korn Shell Operators
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Home Directory

{

Start Code Block

Comment

}

End Code Block

Variable Expressions

;

Shell Command Separator

Background Job

Strong Quote

String Wildcard

Weak Quote

(

Start Subshell

Input Redirect

)

End Subshell

Output Redirect

Quote Next Character

Pathname Directory Separator

Pipe

Single-character Wildcard

[

Start Character-set Wildcard

]

End Character-set Wildcard

Substitutions
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${varname:-word}

Return a default value if varname is undefined

${varname:=word}

Set a variable to a default value if varname is undefined

${varname:?message}

If varname is undefined, print message and terminate script.

${varname:+word}

If varname exists, return word, otherwise return nothing.

Regular Expression Operators
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Operators

Examples

Operator

Meaning

Expression

Matches

*(exp)

0 or more occurrences of exp

*(x)

Null string, x, xx, xxx,...

+(exp)

1 or more occurrences of exp

+(x)

x, xx, xxx, ...

?(exp)

0 or 1 occurrences of exp

?(x)

Null string, x

@(exp1|exp2|...)

exp1 or exp2 or ...

@(x)

!(exp)

Anything that does not match exp

!(x)

Any string except x

Double Operators
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Syntax

Meaning

statement1 && statement2

Execute statement1, and if its exit status is 0, execute statement2

statement1 || statement2

Execute statement1, and if its exit status is not 0, execute statement1.

String Comparison Operators
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Operator

True If...

Operator

True If...

str=pat*

str matches pat

str1>str2

str1 is greater than str2

str!=pat

str does not match pat

-n str

str is not null (has length greater than 0)

str1<str2

str1 is less than str2

-z str

str is null (has length 0)

Test Operators
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These are the operators used with the [[...]] construct.
They can be logically combined with && ("and") and || ("or") and grouped with parentheses.

Operator

True If...

Operator

True If...

-a file

file exists

-x file

You have execute permission on file, or directory search permission if it is a directory.

-d file

file is a directory

-G file

Your group ID is the same as that of file.

-f file

file is a regular file (i.e. not a directory or other special type of file)

-L file

file is a symbolic link.

-r file

You have read permission on file

-O file

You own file.

-s file

file exists and is not empty

file1 -nt file2

file1 is newer than file2

-w file

You have write permission on file

file1 -ot file2

file1 is older than file2.

Arithmetic and Relational Operators
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Arithmetic Operators

Relational Operators

Operator

Meaning

Operator

Meaning

Plus

Minus

Less than

Times

Greater than

Division (with truncation)

Less than or equal to

Remainder

Greater than or equal to

Bit-shift left

Equal

Bit-shift right

Not equal

Bitwise and

Logical and

Bitwise or

Logical or

Bitwise not

Bitwise exclusive or

Typeset Options
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These are the arguments to the typeset command.

With no option, create local variable within function.

-L

Left justify and remove leading blanks.

-R

Right justify and remove trailing blanks.

-f

With no arguments, prints all function definitions.

-f fname

Prints the definition of function fname.

Prints all function names.

-ft

Turns on trace mode for named function(s).

+ft

Turns off trace mode for named function(s).

-fu

Defines given name(s) as autoloaded function(s).

-i

Declare variable as integer.

-l

Convert all letters to lowercase.

-r

Make variable read-only.

-u

Convert all letters to uppercase.

-x

Export variable, i.e., put in environment so it is passed to subshells.

Contents

Invocation OptionsBack to top Table of Contents.

Built-in Commands and KeywordsBack to top Table of Contents.

Built-in Shell VariablesBack to top Table of Contents.

set -o OptionsBack to top Table of Contents.

Basic Korn Shell OperatorsBack to top Table of Contents.

SubstitutionsBack to top Table of Contents.

Regular Expression OperatorsBack to top Table of Contents.

Double OperatorsBack to top Table of Contents.

String Comparison OperatorsBack to top Table of Contents.

Test OperatorsBack to top Table of Contents.

Arithmetic and Relational OperatorsBack to top Table of Contents.

Typeset OptionsBack to top Table of Contents.

Invocation Options
Back to top Table of Contents.

Built-in Commands and Keywords
Back to top Table of Contents.

Built-in Shell Variables
Back to top Table of Contents.

set -o Options
Back to top Table of Contents.

Basic Korn Shell Operators
Back to top Table of Contents.

Substitutions
Back to top Table of Contents.

Regular Expression Operators
Back to top Table of Contents.

Double Operators
Back to top Table of Contents.

String Comparison Operators
Back to top Table of Contents.

Test Operators
Back to top Table of Contents.

Arithmetic and Relational Operators
Back to top Table of Contents.

Typeset Options
Back to top Table of Contents.