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So true. Every time I have to look up how to write a bash for loop. Where does the semicolon go? Where is the newline? Is it terminated with
done? Or withend? The worst part with bash is that when you do it wrong, most of the time there is no error but something completely wrong happens.It all makes sense when you think about the way it will be parsed. I prefer to use newlines instead of semicolons to show the blocks more clearly.
for file in *.txt do cat "$file" doneThe
doanddoneserve as the loop block delimiters. Such as{and}in many other languages. The shell parser couldn't know where stuff starts/ends.Edit: I agree that the
then/fi,do/donecase/esacare very inconsistent.Also to fail early and raise errors on uninitialized variables, I recommend to add this to the beginning of your bash scripts:
set -euo pipefailOr only this for regular sh scripts:
set -eu-e: Exit on error-u: Error on access to undefined variable-o pipefail: Abort pipeline early if any part of it fails.There is also
-xthat can be very useful for debugging as it shows a trace of every command and result as it is executed.set -euo pipefailFun fact, if you’re forced to write against POSIX shell, you aren’t allowed to use these options, since they’re not a thing, which is (part of) the reason why for example Google doesn’t allow any shell language but bash, lol.
Btw, all three set options given above are included in POSIX since 2024: https://pubs.opengroup.org/onlinepubs/9799919799/
Ooh, you’re totally right!! I forgot about that since it’s not in the older versions.
I can only remember this because I initially didn't learn about
xargs--- so any time I need to loop over something I tend to usefor var in $(cmd)instead ofcmd | xargs. It's more verbose but somewhat more flexible IMHO.So I run loops a lot on the command line, not just in shell scripts.