Summary

This post shows how to customize $PATH, an environment variable, in Fish shell.

How-to

Here shows how to add to $PATH, for example.

1. Set Temporarily

All what to do is run this command:

$ set -x PATH <some-path> $PATH

Well, set's -x (or --export) means it "causes the specified shell variable to be exported to child processes (making it an "environment variable")".

2. Set Permanently

2-1. config.fish

Fish shell has $HOME/.config/fish/config.fish as .profile to other shells. Append this line to the bottom of it:

  ...
+ set PATH <some-path> $PATH

2-2. fish_user_paths

There is another and more "fisher" way. Use its fish_user_paths, a universal variable of Fish shell.
Open your terminal and run this command:

$ set -U fish_user_paths <some-path> $fish_user_paths

-U (or --universal) means it "causes the specified shell variable to be given a universal scope".

Be careful not to write it in config.fish, which is called every time Fish shell starts.