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kiri
Asked: 2013-10-12 00:52:15 +0800 CST

How do I execute a program with default variables?

  • 772

How can I execute a program (specifically a bash alias) with the default environment variables?

Consider this example:

export test="something I dont want to exist"

alias _xterm='xterm -fn 7x13 -fa "Ubuntu Mono:size=12:antialias=false"'

_xterm

In the spawned xterm instance, the variable $test shouldn't be set.

bash

2 Answers

  1. Best Answer

    You could execute your command in an empty environment:

    env -i _xterm

    A quick test harness:

    $ export TMUX=3
$ bash -c 'echo $TMUX'
3
$ env -i bash -c 'echo $TMUX'
# nothing echos

    Preserving $DISPLAY, $USER, etc:

    $ env -i bash -c 'echo $DISPLAY'
# nothing
$ env -i DISPLAY=$DISPLAY bash -c 'echo $DISPLAY'
:0

    Or you could explicitly exclude just some variables with the env -u option:

    $ export TMUX=3
$ env -u TMUX bash -c 'echo $TMUX'
# nothing
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  2. The names of default environment variables are written with capital letters. Now, assuming that you will define new environment variables with tiny letters (as it is in your example test), instead to use a simple alias _xterm, you can use a function _xterm where you have to unset the new environment variables and keep only the default environment variables for the new shell instance:

    _xterm () {
    for var in $(env | cut -d"=" -f1)
    do
        if [[ ! "$var" =~ [^a-z] ]]; then
            unset $var   #or env -u $var
        fi
    done
    xterm -fn 7x13 -fa "Ubuntu Mono:size=12:antialias=false"
}

    Like this, your new environment variables are not available in the new shell instance, but when you comeback to the old shell instance you can still use them.

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