Bash Cookbook

Conditional logic using if, else, and elseif

The previous section introduced the concept that there are several reserved words and a number of characters that have an effect on the operation of Bash. The most basic, and probably most widely used conditional logic is with if and else statements. Let's use an example code snippet:

#!/bin/bashAGE=17if [ ${AGE} -lt 18 ]; then echo "You must be 18 or older to see this movie"fi

Notice the space after or before the square brackets in the if statement. Bash is particularly picky about the syntax of bracketing.

If we are evaluating the variable age using less than (<) or -lt (Bash offers a number of syntactical constructs for evaluating variables), we need to use an if statement. In our if statement, ...