Shell scripting is notoriously full of pitfalls, unintuitive behavior and poor error messages. Here are some things you might have experienced:

find -exec fails on commands that are perfectly valid

0==1 is apparently true

Comparisons are always false, and write files while failing

Variable values are available inside loops, but reset afterwards

Looping over filenames with spaces fails, and quoting doesn’t help

ShellCheck is my latest project. It will check shell scripts for all of the above, and also tries to give helpful tips and suggestions for otherwise working ones. You can paste your script and have it checked it online, or you can downloaded it and run it locally.

Other things it checks for includes reading from and redirecting to a file in the same pipeline, useless uses of cat, apparent variable use that won’t expand, too much or too little quoting in [[ ]], not quoting globs passed to find, and instead of just saying “syntax error near unexpected token `fi'”, it points to the relevant if statement and suggests that you might be missing a ‘then’.

It’s still in the early stages, but has now reached the point where it can be useful. The online version has a feedback button (in the top right of your annotated script), so feel free to try it out and submit suggestions!