Modifying PATH with fish shell

As stated in the official fish tutorial, you can modify the $fish_user_paths universal variable.

Run the following once from the command-line:

set -U fish_user_paths /usr/local/bin $fish_user_paths

This will prepend /usr/local/bin permanently to your path, and will affect the current session and all future instances too because the -U argument will make the variable universal.

From the fish documentation:

... (Note: you should NOT add this line to config.fish. If you do, the variable will get longer each time you run fish!)

fish_user_paths, a list of directories that are prepended to PATH. This can be a universal variable.

As of fish 3.2.0, released in March 2021, the canonical answer is:

fish_add_path /opt/mycoolthing/bin

Existing answer for fish < 3.2.0:

The recommended commands for modifying PATH from fish's maintainers are:

1. If you want to run the command once:

   set -Ua fish_user_paths /path

2. If you want to add a command to a startup script, this is idempotent:

    contains /path $fish_user_paths; or set -Ua fish_user_paths /path

Like all shells, fish inherits its PATH from the environment it is started in. How this is set for login shells differs between operating systems - on Linux, for example, /etc/login.defs controls the initial PATH set for all login shells. I don't know how this is set on OS X.

Next, like bash or csh, the initialisation files for the shell may alter the path. For fish on OS X, there is code in share/fish/config.fish to load paths from the standard OS X path configuration files /etc/paths and /etc/paths.d/*. There is alternative code to set a useful path on Solaris.

There is also code to pick up paths from the universal variable $fish_user_paths, which is the right way to add something to your PATH and have it reflected across all shells.