Enviroment variables using fish shell

Overview

Sometimes we need to export some value as an env var (eg. android sdk path). It is important to know how to do this well for smooth system administration.

Each shell has its own way to manage environment, I'm using fish shell.

In order to list current vars, standard env command is available.

Local env vars

We could run an app with custom enviroment vars, like this:

env LALA='foo bar' some_cmd

This does not always work, because env bypasses our shell.

In those situations, we could use set instead:

set -lx LALA='foo bar'; some_cmd

The -l switch means local scope, the variable is temporal.

Persistent env vars

When we need env vars to be persistent only across a session, we use global ones (-g switch):

set -gx LALA='foo bar'
some_cmd
other_cmd

Finally, we could use universal env vars, which are fully persistent across multiple sessions (-U switch).

For example, I used them in order to configure android sdk, like this:

set -U ANDROID_HOME /path/to/android/sdk

Universal env vars are persistent across reboots, you can inspect them using set -U cmd.

Path management

Changing the PATH env var is an special case. We cannot modify it directly, because it could be overwritten by the shell.

In order to overcome this situation, fish provides the fish_user_paths variable, which is automatically merged to PATH.

We could add some custom bin directory (e.g. node_modules bin dir), like this:

set -U fish_user_paths $fish_user_paths /path/to/node_modules/bin

In this way we preserve previously added paths, and the new dir is only appended to fish_user_paths.

The shell automatically adds the custom paths to the PATH var each time a session is started.