I feel like I’m overdue for learning she’ll scripting properly. I’ve hacked around for years google as I go.
What resources would you suggest for decent training material?
What resources would you suggest for decent training material?
(Usually available locally at 'info bash', I know you hate info don't @ me)
The one resource that I have bookmarked decades ago and would highly recommend to get the ball rolling are the TLDP pages on bash:
https://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html
https://tldp.org/LDP/Bash-Beginners-Guide/html/index.html
https://tldp.org/LDP/abs/html/
Not certain if they’re up to date or error free but I really enjoy the style and tutorial/show by example nature of the TLDP
What I've done is, every time I came across something that didn't behave the way I expected, I tried to Google it and tinker around with it until I could understand exactly what is going on, so that I "got" the underlying feel for the language and didn't have to look up every consequence every time. e.g., the difference between [ ] and [[ ]], which is confusing at first, becomes more intuitive once you realize [ is a portable POSIX command whereas [[ is special Bash syntax, and once you grasp this, you can understand what its implications are. e.g., that Bash has no way to detect '=' as a special token inside [ ], and consequently you should worry about ambiguities. (This does assume a little background knowledge of parsing ambiguities; if you haven't taken a course related to programming languages, going through one might also be a worthwhile investment.)
Also, you have to be on the lookout for things that you would want to do in a different language, and learn how to do it in Bash, like creating functions & local variables. It's mostly a matter of being proactive about learning how to structure your code like you would in other languages. Often I see people try to keep things "simple" by just copy/pasting code so that they don't have to organize things at a higher level. You wouldn't do that in other languages; don't do that in Bash.
Some pitfalls you really just do have to learn the hard way; there's no other way I can think of. The key here is to spend the extra minutes necessary to actually learn what broke when you come across it, instead of just tinkering with your code until it works. Like when you realize that (set -e; false && false; echo hi) prints 'hi' despite the fact that (set -e; false; echo hi) does not (this is absolutely bonkers), dig in and figure out what's going on so you don't shoot yourself in the foot the next time. You can't avoid it the first time, but you can at least make sure to avoid it in the future.
Also, always try to think of unintended consequences when you learn how to do something in Bash. Like when you learn how `trap 'rm -f file.bak' EXIT` lets you clean up a file, ask yourself what happens if someone has already set a trap? Ask yourself how to dynamically generate and pass a file name to that command safely? Ask yourself in what scope/context the command is evaluated? Spend some time figuring these out either online or by tinkering manually, then remember your solution for later (maybe write it down). Possibly the most costly mistake you can make is to assume something will work in exactly the same way you expect in every other language, because chances are pretty darn good it won't. Even pipelines (which you probably already use) are tricky if you start thinking about them... e.g., what happens if the first command terminates prematurely? What happens if you assign to a variable? etc.
Some sites I can recommend for some things:
- https://pubs.opengroup.org/onlinepubs/9699919799/utilities/s...
- https://tldp.org/LDP/abs/html/index.html
- https://mywiki.wooledge.org/BashPitfalls
The POSIX pages (OpenGroup, first link) are useful for understanding what you can rely on; I'd use that as a command reference whenever it's possible. In some cases they're overly pessimistic (e.g., you can probably rely on 'local' despite it not being POSIX), but generally they're good starting points.
tldp is where I still look up some things, like the heredoc syntax. I've probably looked that up 20 times and I still don't remember it well enough for some reason.
And it might be fun to just browse through the BashPitfalls page once you have some comfort with shell scripting just to get an idea of what can go wrong, but I wouldn't really recommend it as a learning guide, and you definitely shouldn't expect to memorize all of it.