i didnt care about how i wrote my bash scripts, coz i know theyd ultimately be used just by myself. but for the past few day, i've been working on this project, mk-blog which uses some bash scripts, there are chances that others might look at them. besides in work they're asking me maintain a server. so why not learn the standards. but i couldn't find anything good online (i'm gonna blame my search engine lol). so...
i'd appreciate redirections to (official or community) bash coding standards
If your bash script gets longer than 200 lines (including argument handling), use Python. I have to support bash APPLICATIONS at work and it's a fucking nightmare to maintain.
I would then assume those scripts weren't written properly to begin with.
But yes, shell scripts should be used (normally) to automate some simple tasks (file copying, backups...) or as an wrapper to exec some other program. I've written several shell scripts to automate things on my personal machines.
However shell script can be complex program while at the same time being (somewhat) easy to maintain:
functions, use functions, alot
comment every function and describe what it expects in stdin or as an arguments
also comment what it outputs or sets
This way at least I don't break my scripts, when I need to modify a function or some way extend my scripts. Keeping the UNIX philosophy inside shell scripts: let one function do one thing well.
And of course: YMMV. People have wastly different coding standards when it comes to personal little(?) projects.
Don't know about everyone else, but here are some of mine:
Stick to posix compliance shell code, wherever possible
Please wrap your variables with { }. Just please.
Global variables being exported in all caps
Local variables in lower case
$() instead of ` `
Comment anything complicated, comment what section, comment usage
Include usage output if options are not recognized
Use case instead of if / elif, where possible
80 characters or less per line, where possible
HERE docs in designated section, marked by comment blocks
Comment your functions immediately above it's definition
Add comment "#End of function Xyz" at line immediately below a function, with replacing Xyz with name of that function
2 space indentation
Multi-line strings: First line open with quote and first line of string, followed by a backslash , subsequent lines properly indented and backslashed. Last line, properly indented and close quoted.
Break up multiple piping of commands with |\ and a new line where it makes sense to look nice, assisting readability
Echo what the script is doing once in a while if the user will be waiting for a while
Please don't do shar archives, or byte located binary extractions, make a script and a separate tarball - Helps a ton if we have to change it, like say... swapping out a bundled java runtime built for x86_64 with one for aarch64
If the script will run for a very long time, check for tmux or screen and also the TMOUT variable... Give a warning to the user their connection might time out before the script is done if they don't unset TMOUT, and try using tmux or screen to allow the script to continue in the background, even if you do get disconnected
Make use of logger
I try to organize a script this way: 1. Shebang, 2. Initial variable definitions, 3. Functions, 4. runtime execution code, which might be best outside of a function, and calling functions. 5. Clean-up (remove pid and lock files, tmp files, etc etc.)
utilize awk if you need to process (=more complex than just grepping) large amounts of text.
make your awk code conform to at least busybox awk for compability
I once did a sh script that needed (because I wanted a challenge?) to be compatible with vanilla Android shell too.
So I needed to test it with regular bash, busybox and mksh+toybox. That was 'fun'.
I've had some initial plans to spllit the code out from that project and develop a "shell" library that would ease building shell scripts that are compatible with different systems...
But I bet someone else has already done that.
There is no single Bash standard to follow, only a few guidelines. One way you can check for some basic errors and formatting would be using an editor with support for Bash (in best case with a builtin LSP). At the end, you have to find your style and coding standards or adapt what others do if you want work with them or edit their files.
Otherwise there is a well known tool for checking Bash files: https://www.shellcheck.net/ You can use it online and as a downloaded program on your local machine. After using shellcheck for a bit I got used to some of its conventions and recommendations, such as always wrapping variables like in ${variable} and some other things.
Related is the Bash Reference Manual from GNU: https://www.gnu.org/software/bash/manual/bash.html Off course this is not a guide on how to style or program, but it helps in understanding how GNU does things.