Update: I'm no longer using this, I'm testing out using bass instead

The behavior is a bit different from source, as source runs the content of a script, while fs runs the script, pipes the output to a file, and then runs the output. So the script being run through fs must use echo export A=hello instead of using export A=hello.

Ideally, we want to use a pure source. We can do this instead by using the bass plugin. Setup:

fisher install edc/bass
alias fs="bass source"
funcsave fs

The alias stuff is just so we don't have to write the lengthy bass source mycommand when we want to source mycommand.

Fish source

Fish source ("fs") emulates source. It executes the output of a command in the current Fish shell.

Usage

Example:

We have a file some-command somewhere in the $PATH, and it contains this:

cd /

If you run this command from the directory /tmp

/tmp $ fs some-command

then your shell will now be in the root directory:

/ $

Just like source.

Why?

TL;DR: source in Fish shell ignores $PATH, but fs does not.

Fish's documentation states

fish will search the working directory to resolve relative paths but will not search PATH.

This is very unhandy, as being able to source the output of all commands in $PATH is very useful. fs solves this.

Alternative

Install the the bass plugin, and use bass source mycommand.

Installation

Using fisher

fisher install yngvark/fs

Directly

Put fs.fish into ~/.config/fish/functions:

wget https://raw.githubusercontent.com/yngvark/fish-source/main/functions/fs.fish -O ~/.config/fish/functions/fs.fish