Command line wizardry, part two: Variables and loops in Bash

By | September 20, 2021

Enlarge / Getting the hang of iteratively building commands interactively is all it really takes to become a command line wizard. (credit: Bashar Shglila / Getty Images)

In our first tutorial on command line wizardry, we covered simple redirection and the basics of sed, awk, and grep. Today, we’re going to introduce the concepts of simple variable substitution and loops—again, with a specific focus on the Bash command line itself, rather than Bash scripting.

If you need to write a script for repeated use—particularly one with significant logical branching and evaluation—I strongly recommend a “real language” instead of Bash. Luckily, there are plenty of options. I’m personally a big fan of Perl, in part because it’s available on pretty much any *nix system you’ll ever encounter. Others might reasonably choose, say, Python or Go instead, and I wouldn’t judge.

The real point is that we’re focusing on the command line itself. Everything below is something you can easily learn to think in and use in real time with a little practice.

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