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 its command-centered structure, and only partly resembles comparable features in other programming languages.
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