The if-then-fi Structure

The if-then-fi Structure

The if-then-fi structure is used to check a condition with the help of a test command. If the test returns a true value, then an action is performed. If the test returns a false value (not true), the action part of the program is not executed.

Synopsis :

if
      list A
then
      list B
fi

A summary of the execution of the if construct is as follows :
1. Command list A is executed.
2. If the return code of the last command in command list A is a 0 (TRUE), execute command list B, then continue with the first statement following the fi.
3. If the return code of the last command in command list A is not zero (FALSE), jump to fi and continue with the first statement following the fi.

Flow chart of if-then-fi Structure

Example of if-then-fi structure

The test command is commonly used to control the flow of control, but any command can be used, since all Linux system commands generate a return code