Bash tab completion not working following = character

Question

I've looked at a lot of bash tab completion questions and haven't yet found one that answers this one.

I'm on a linux system (GNU bash, version 4.2.46(2)-release (x86_64-redhat-linux-gnu)) and normally tab completion works just fine.

However, when I go to use tab completion for an environment variable or command-line option, it fails. For example,

ls /v<TAB> -> ls /var/
export FOO=/v<TAB> -> export FOO=/v (bell plays)

When I do this on my Mac (GNU bash, version 5.0.16(1)-release (x86_64-apple-darwin18.7.0)) tab completion of the environment variable value works fine.

On both machines, $COMP_WORDBREAKS is "'><=;|&(:.

Someone (I don't know where this came from) suggested that

shopt -u progcomp

might help, and it does fix the problem! However, I don't need to unset that option Mac-side and I'm worried it might cause other strange side effects.

Is that a normal thing to unset? Is there anything else I can do to figure this out?

Answer 1

shopt -u progcomp disables programmable completion, i.e. scripts that may provide e.g. per-program completion. They might provide features like only completing files that match *.tar or such when the command line starts with tar, etc. Those scripts usually come with your distribution, or not, in the case of the Mac.

It's fine to disable progcomp if the bugs and misfeatures caused by those scripts seem more annoying than the actual features are useful (and for me, that's about 100 % of the time).