Korn shell variables

Variables are set with the operator as in Bourne shell. No space is allowed around the = operator. Variables may have attributes assigned by typeset with the following syntax:

Korn Shell typeset syntax
typeset -attrib(s) variable=[value]	assign attribute and optional value
typeset +attrib(s) variable	remove attribute
typeset	list all vars and attributes
typeset -attrib	list all vars with -attrib type
typeset +attrib	list only vars with +attrib type
List of typeset Supported Attributes
-f	the name refers to a function
-H	system to hostname file mapping
-i	integer
-l	lower case
-L	left justify, remove leading spaces
-LZ	left justify, remove leading zeroes
-r	read only (cannot be removed)
-R	right justify
-RZ	right justify with leading zeroes
-t	tag named parameter
-u	upper case
-x	export

Any variable can be assigned the output of a command or of a file with the syntax:

var=$(command)	Korn specific
var=`command`	Bourne compatible
var=$(< file)	Korn specific
var=`cat file`	Bourne compatible

Variables are removed by the unset builtin. To define a variable that executes a script file using Ksh syntax, do the following:

> ksh
$ cv=$(<kls)
$ echo $cv
ls -al
$
$ $cv
total 5
drwxr-xr-x   3 john     users       8192 Mar 10 10:48 .
drwxr-x--x  17 john     users       8192 Mar  9 16:05 ..
-rw-r--r--   1 john     users        299 Mar  9 11:25 a.a
-rwxr-xr-x   1 john     users        261 Mar 10 08:44 cread
-rw-r--r--   1 john     users         37 Jun 18  1998 er

Ksh Special variables are:

Korn Shell Special Variables
#	number of positional parameters
?	exit status
$	process ID
- (dash)	current options
_ (underscore)	the last argument of the previous command
!	process ID of last background
ERRNO	error no. of last failed system call
LINENO	the line no. of the current script line in execution
OLDPWD	previous cd directory
OPTARG	last option processed by getopts
OPTIND	index of last option processed by getopts
PPID	parent PID
PWD	current directory
RANDOM	random funcion
REPLY	menu item no. in response to select Ksh command
SECONDS	seconds since shell invocation
CDPATH	search path for cd command
COLUMNS	edit window width
EDITOR	editor management
ENV	generate path name in tracked alias and functions
FCEDIT	default editor for history processing command fc
FPATH	search path for functions
IFS	internal field separator
HISTFILE	store command history file
HISTSIZE	history buffer size
HOME	home directory
LANG	system locale
LC_COLLATE	collating sequence
LC_CTYPE	character classification
LC_MESSAGES	language for system messages
LC_MONETARY	monetary format
LC_NUMERIC	numeric format
LC_TIME	date and time format
LINES	column length
LOGNAME	login name
MAIL	mail notify
MAILCHECK	mail notify interval
MAILPATH	mail notify
NLSPATH	search path for messages
PATH	searc path for commands
PS1	primary promt
PS2	secondary prompt
PS3	selection prompt (default #?)
PS4	trace prompt (default +)
SHELL	shell in use
TMOUT	command timeout to terminate shell
VISUAL	editor option

Variables are protected by braces:

$ print Current options/ERRNO: ${-}, $ERRNO
Current options/ERRNO: ism, 10

Metacharacters are printed when prefixed by \.

Korn Shell Variable Usage and Setting Rules
varlen=${#var}	variable length
var=${var1:-value}	var=var1 if var1 set, var=value if var1.not.set or empty
var=${var1-value}	var=var1 if var1 set, var=value only if var1.not.set
var=${var1:=var2}	var=$var1 if var1 set and not empty, else = $var2
var=${var1=var2}	var=$var1 if var1 set even if empty, else = $var2
var=${var1:+var2}	var=$var2 if var1 set and not empty, else var not set
var=${var1:+var2}	var=$var2 if var1 set even if empty, else var not set
var=${var1#var2}	var=var1 with smallest part of left matched var2 deleted
var=${var1##var2}	var=var1 with largest part of left matched var2 deleted
var=${var1%var2}	var=var1 with smallest part of right matched var2 deleted
var=${var1%%var2}	var=var1 with largest part of right matched var2 deleted
var=${var1:?}	var=var1 if var1 set else error message
var=${var1:?var2}	var=var1 if var1 set else var=var2 and exit

Korn shell can handle arrays as C shell but with a different syntax.

Korn Shell Array Syntax
arr[0]=val0 arr[1]=val1 ...	init array in any order
set -A arr val0 val1 ...	alternate init for ordered array
typeset arr[0]=val0 arr[1]=val1 ...	alternate init array in any order
${arr}, $arr	array element zero
${arr[n]}	array element n
${arr[n+2]	array element n+2
${arr[$i]}	array element $i
${arr[*]}, ${arr[@]}	all elements of array
${#arr[*]}, ${#arr[@]}	number of array elements
${#arr[n]}	length of array element n

Example of array usage:

#!/bin/ksh
#-----------karray: arrays with Korn shell
#
echo Proc $0: arrays in Korn shell
echo
set -A rgb red green blue yellow magenta cyan
print rgb is a ${#rgb[*]} items color array with values:
print ${rgb[*]}
print 4-th item is ${rgb[1+3]} ${#rgb[4]}-bytes long
#
#----------end script------------------

The set +A statement allows partial redefinition of ordered array elements. Consider the following:

$ set -A rgb red green blue yellow magenta cyan
$ print ${rgb[*]}
red green blue yellow magenta cyan

If you use -A to change only the first item of array rgb, the array is truncated. If you use +A, the first items are changed keeping the remaining ones:

$ set -A rgb red green blue
$ print ${rgb[*]}
red green blue
$ set -A rgb red green blue yellow magenta cyan
$ set +A rgb rosso
$ print ${rgb[*]}
rosso green blue yellow magenta cyan

In Korn shell quotes have the same usage as in Bourne shell.

single quotes ' 		 hide meaning of special characters, do not perform


variable substitution within quoted string

double quotes " 		 preserve embedded spaces and newlines, set vars to 
		 NULL, display single quotes, perform variable   substitution

back quotes ` 		 assign command output to vars