Add a relative path to $PATH on fish startup

The best way I have found to persistently add a path to your $PATH is

set -U fish_user_paths $fish_user_paths ~/path/name

This prepends to $PATH. And since it’s persistent, the path stays in $PATH on shell restarts.

It’s more efficient than putting a command in your config.fish to modify your $PATH, because it only runs once compared to running on every shell restart.

The variable fish_user_paths is intended to be set by the user¹, as stated by ridiculousfish, the maintainer of fish.

Consider creating a fish function for convenience: ²

# ~/.config/fish/functions/add_to_path.fish
function add_to_path --description 'Persistently prepends paths to your PATH'
  set --universal fish_user_paths $fish_user_paths $argv
end

And use it as:

$ add_to_path foo bar  # Adds foo/ and bar/ to your PATH

Notes

1. On that page the author gives the example set -U fish_user_paths ~/bin. This overwrites fish_user_paths with a single value of ~/bin. To avoid losing existing paths set in fish_user_paths, be sure to include $fish_user_paths in addition to any new paths being added (as seen in my answer).

2. My dotfiles contain a slightly more advanced version that skips adding duplicates https://github.com/dideler/dotfiles/blob/master/.config/fish/functions/add_to_user_path.fish