Last night, I was trying to figure out where a particular environment variable had come from, and went searching¹ for a way to figure that out. I was delighted, as I often am, to find that fish makes it incredibly easy. If you want to know where and how SOME_ENVIRONMENT_VARIABLE was set, you just type:

$ set --show SOME_ENVIRONMENT_VARIABLE

Fish will helpfully print out something like this (assuming SOME_ENVIRONMENT_VARIABLE was set to the string cool-beans, and was set with set -Ux SOME_ENVIRONMENT_VARIABLE cool-beans):

$SOME_ENVIRONMENT_VARIABLE: set in universal scope, exported, with 1 elements
$SOME_ENVIRONMENT_VARIABLE[1]: |cool-beans|

This is one of those things that feels obvious once you first see it in action, and yet…

As far as I know — and I’d be happy to be informed otherwise, and will update this if someone tells me otherwise — there’s no good way to do this in bash or zsh! Indeed, fish only got this capability a few years ago (in 3.6.0). You can read more in the fish docs.