Bash Scripting: Control Structures

In Bash scripting, control structures allow you to make decisions based on conditions and perform different actions depending on the result. There are two types of control structures: the if statement and the case statement.

The if statement

The if statement is used to test a condition and perform different actions depending on whether the condition is true or false.

Here is the basic syntax of the if statement:

Let's break down the different parts of this syntax:

• if: This keyword starts the if statement.
• [ condition ]: This is the condition that we want to test. Note that there is a space after the opening bracket and before the closing bracket.
• then: This keyword indicates that we are about to execute a command if the condition is true.
• # do something if the condition is true: This is the command that will be executed if the condition is true.
• else: This keyword indicates that we are about to execute a command if the condition is false.
• # do something else if the condition is false: This is the command that will be executed if the condition is false.
• fi: This keyword ends the if statement.

Here is an example that shows how the if statement can be used:

This script checks if the /etc directory exists and if it is a directory. If it is, then it prints out the message " /etc is a directory". If it is not, then it prints out the message " /etc is not a directory".

The case statement

The case statement is used to test a value against a list of possible patterns and perform different actions depending on which pattern matches.

Here is the basic syntax of the case statement:

Let's break down the different parts of this syntax:

• case: This keyword starts the case statement.
• $variable: This is the value that we want to test against the list of patterns.
• in: This keyword indicates that we are about to list the patterns.
• pattern1): This is the first pattern that we want to test. Note that the pattern ends with a closing parenthesis.
• # do something if $variable matches pattern1: This is the command that will be executed if the value of $variable matches pattern1.
• ;;: This keyword ends the command for this pattern and starts the next pattern.
• pattern2): This is the second pattern that we want to test.
• # do something if $variable matches pattern2: This is the command that will be executed if the value of $variable matches pattern2.
• ;;: This keyword ends the command for this pattern and starts the next pattern.