Linux Shell Scripting Cookbook - Second Edition

Comparisons and tests

Flow control in a program is handled by comparison and test statements. Bash also comes with several options to perform tests that are compatible with the Unix system-level features. We can use if, if else, and logical operators to perform tests and certain comparison operators to compare data items. There is also a command called test available to perform tests. Let us see how to use these.

How to do it...

We will have a look at all the different methods used for comparisons and performing tests:

• Using an if condition:

  if condition;
  then
      commands;
  fi

• Using else if and else:

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

  Note

  Nesting is also possible with if and else. The if conditions can be lengthy, ...