Share environment variables between bash and fish

bash has special syntax for setting environment variables, while fish uses a builtin. I would suggest writing your .env file like so:

setenv VAR1 val1
setenv VAR2 val2

and then defining setenv appropriately in the respective shells. In bash (e.g. .bashrc):

function setenv() { export "$1=$2"; }
. ~/.env

In fish (e.g. config.fish):

function setenv; set -gx $argv; end
source ~/.env

Note that PATH will require some special handling, since it's an array in fish but a colon delimited string in bash. If you prefer to write setenv PATH "$HOME/bin:$PATH" in .env, you could write fish's setenv like so:

function setenv
    if [ $argv[1] = PATH ]
        # Replace colons and spaces with newlines
        set -gx PATH (echo $argv[2] | tr ': ' \n)
    else
        set -gx $argv
    end
 end

This will mishandle elements in PATH that contain spaces, colons, or newlines.

The awkwardness in PATH is due to mixing up colon-delimited strings with true arrays. The preferred way to append to PATH in fish is simply set PATH $PATH ~/bin.

Most Unix systems use PAM. The pam_env module reads a file very much like your .env.

On Linux, pam_env reads a system file /etc/environment and a user file ~/.pam_environment. On OS X (and other *BSD, which likewise use OpenPAM), it appears that pam_env only reads the system file, so you can't set variables per user this way, only for all users.

There is (now?) an easier way, per @Zanchey's answer here

Fish Shell: How to set multiple environment variables from a file using export

The digest though is:

Fish:

echo -e "foo=3\nfoobar=4" > .env; export (cat .env); env | grep foo

Bash:

echo -e "foo=3\nfoobar=4" > .env; export $(cat .env | xargs); env | grep foo

with the difference being $ and the use of xargs