Perl support in Liquidprompt

A long long time ago I fell over Liquidprompt and I used it for a long time, running on my own fork, which had support for perlbrew implemented by me, nothing like scratching your own itch.

Back in the day I sent a pull request to the original author, but it was never merged, I had some dialogue with the new maintainer, but never got around to porting the code to the latest version of Liquidprompt.

Now that I decided to join the 24 PRs, I decided to give it another go.

So here it is, a PR with a new implementation of Perlbrew support to the latest version of Liquidprompt and as a bonus, I also added support for plenv and alternative to Perlbrew for handling your Perl installations.

One interesting part I want to highlight is this Bash thing. I had to get GitHub co-pilot to explain it to me.

plenv resembles rbenv so I could basically reuse the implementation of rbenv. The two emit a somewhat similar string:

rbenv version
3.2.2 (set by /Users/jonasbn/.rbenv/version)

plenv
5.10.1 (set by /Users/jonasbn/.plenv/version)

And these can be handled by a Bash contruct like this:

"${plenv_ver%%" (set"*}"

Perlbrew however emits version strings like so:

perlbrew use
Currently using perl-5.38.0

So I needed to get my head around: %% and I needed something along those lines, but removing part of the string, isolating the version string.

I found this Bash documentation and a marvellous question with a some goood examples which could be used to speed up the implementation, since it could be done on the command line using Bash.

The operator is called: ## and it is used for removing a prefix pattern, where %% is used for removing a suffix pattern.

And in Bash you can do something along the following to test your code faster:

perlbrew_perl_ver="Currently using perl-5.38.0" && echo "${perlbrew_perl_ver##}"

I did that and kept adding to the pattern until I got the result I wanted and I ended up with this implementation:

"${perlbrew_perl_ver##*perl-}"

From the documentation for: %% used for plenv and rbenv:

${parameter%%word}
Remove matching suffix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern matches a trailing portion of the expanded value of parameter, then the result of the expansion is the expanded value of parameter with the shortest matching pattern (the ''%'' case) or the longest matching pattern (the ''%%'' case) deleted. If parameter is @ or *, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list.

And for ## used in my own implementation for perlbrew:

${parameter##word}
Remove matching prefix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern matches the beginning of the value of parameter, then the result of the expansion is the expanded value of parameter with the shortest matching pattern (the ''#'' case) or the longest matching pattern (the ''##'' case) deleted. If parameter is @ or *, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list.

This was quite a journey down a rabbit hole, but I got it too work eventually.

Additional resources

• Liquidprompt on github
• Perlbrew on github
• Perlbrew on CPAN
• Perlbrew website perlbrew.pl