Using Array Variables in Shell Scripting

Sometimes you want to store related information in a set of variables and be able to refer to the variables together.
In programming this is commonly done with an array variable. For example, the social security number of each travel agent needs to be stored in a set of variables. You could use a set of variables like this:

agent1=555-99-1212
agent2=555-99-1213
agent3=555-99-1214
agent4=555-99-1215

agent[1]=555-99-1212
agent[2]=555-99-1213
agent[3]=555-99-1214
agent[4]=555-99-1215

This may look very similar to the first set of variables, but for large numbers of variables, arrays are much more efficient. Later in this course you will learn to use a loop with a counter. The counter can be used as the index number to access each element in a large array. Here is an example of how the array element is referred to:

echo agent[$COUNTER]

With regular variables, you must use the full name of each variable, so a loop cannot be used. The regular variables we have been using are calledscalar^[1] variables.
This diagram illustrates the conceptual difference between regular (scalar) variables and array variables.

echo ${agent[@]}

Unfortunately, the Bourne shell does not support array variables. You will not often need them in shell scripts, but if you do, the ksh, tcsh, and bash shells all support array variables.
In the next lesson, we will wrap up this module.

[1] Scalar: A standard or simple variable, as opposed to a variable that contains multiple values (like an array) or one that contains additional information (such as a vector in mathematical terms).