Linux Shell Scripting Cookbook - Third Edition

How to do it...

Here are some methods used for comparisons and performing tests:

• Use an if condition:

        if condition; 
        then 
            commands; 
        fi

• Use else if and else:

        if condition;  
        then 
            commands; 
        else if condition; then 
            commands; 
        else 
            commands; 
        fi 

Nesting is possible with if and else. The if conditions can be lengthy; to make them shorter we can use logical operators:

[ condition ] && action; # action executes if the condition is true

[ condition ] || action; # action executes if the condition is false

&& is the logical AND operation and || is the logical OR operation. This is a very helpful trick while writing Bash scripts. Performing mathematical comparisons: usually, conditions are enclosed in square brackets []. Note that there is a space ...