Bash – Quick directory navigation in the bash shell

You can use the env command to start a process with a clean environment. Here is an example:

env -i /bin/myprog

If you still need to export some variables, you can do so in the call:

env -i MYVAR=foo /bin/myprog

The env command is required by POSIX.

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.