I'm sorry, I don't know how I can help you. I just installed cpanm 1.7044 as a Devuan package (Debian derived Linux) and it installs pl fine with -l /some/dir. (It does create various useless x86_64-linux-gnu-thread-multi subdirs, but that may be their problem and only cosmetic.) I can however confirm that reinstalling does overwrite the script – annoying but again not the end of the world.

Maybe you can find a similarly minimal package as pl is, for you and me to compare? Cpanm is quite the opposite, having so many dependencies.

Or you could open an issue against cpanm, saying that it works on Linux, but not Mac. If you add the output you get from cpanm -v App::pl, they'll probably know right away what's wrong. Or they might have access to a Mac, to find out…

Thank you. This did in fact install with cpanm after your update, I thought it hadn't worked because repeating the install command re-installed it. A similar package to compare with might be Ack.

In other news, there is already an installed program called pl:

$ man pl

NAME
     pl – ASCII property list utility

SYNOPSIS
     pl [--input file] [--output file]

DESCRIPTION
     pl can be used to check the syntax of old-style ASCII property li
+st files.
     ...
[download]

I'm not sure what the best practice is for dealing with name clashes like this. Perhaps giving it a non-clashing name and leaving it up to the user to make a shorter alias ...