Bash Quick Start Guide

Loops and Conditionals

In this chapter, we'll learn how to work with conditionals and then loops in Bash using the if, for, and while shell keywords. These allow us to execute commands conditionally and/or repeatedly, giving us control flow for our scripts.

We will cover:

• How to use the if keyword
• The use of and the difference between the [ builtin and the [[ keyword
• When to use Bash's (( arithmetic compound command
• How to match values with the case keyword
• How shell script for loops work
• Using Bash's alternative C-style for loops
• Using while loops
• The while read -r idiom for reading data line by line
• Choosing between for and while

Shell script's syntax for these structures is somewhat unique, largely for historical reasons and to fit into ...