LiveFire Labs' UNIX Tip, Trick, or Shell Script of the Week

Korn Shell Arrays - Assigning and Accessing Values - Part I

Another type of variable supported by the Korn shell is the array. Briefly, an array contains a collection of values (elements) that may be accessed individually or as a group. Although newer versions of the Korn shell support more than one type of array, this tip will only apply to indexed arrays.

When assigning or accessing array elements, a subscript is used to indicate each element's position within the array. The subscript is enclosed by brackets after the array name:

arrayname[subscript]

The first element in an array uses a subscript of 0, and the last element position (subscript value) is dependent on what version of the Korn shell you are using.  Review your system's Korn shell (ksh) man page to identify this value.

In this first example, the colors red, green, and blue are assigned to the first three positions of an array named colors:

$ colors[0]=RED
$ colors[1]=GREEN
$ colors[2]=BLUE

Alternatively, you can perform the same assignments using a single command:

$ set -A colors RED GREEN BLUE

Adding a dollar sign and an opening brace to the front of the general syntax and a closing brace on the end allows you to access individual array elements:

${arrayname[subscript]}

Using the array we defined above, let's access (print) each array element one by one:

$ print ${colors[0]}
RED
$ print ${colors[1]}
GREEN
$ print ${colors[2]}
BLUE
$

If you access an array without specifying a subscript, 0 will be used:

$ print ${colors[]}
RED
$

The while construct can be used to loop through each position in the array:

$ i=0
$ while [ $i -lt 3 ]
> do
> print ${colors[$i]}
> (( i=i+1 ))
> done
RED
GREEN
BLUE
$

Notice that a variable (i) was used for the subscript value each time through the loop.