sound policy on global variables for "distributed" DWIM function

[Emanuel Berg <embe8573@xxxxxxxxxxxxx>]

I have put together a DWIM function to take
screenshots (or dumps), and it can be invoked in
X just as well as in the console with the wrapper
detecting which one and acting accordingly.

My question is, you see that the data item ".png"
appears in *both* specialized functions (dump-vt and
dump-x), but it is likely that if I ever were to
abandon PNG for some other format, I'd want that for
dumps both of the VTs and X.

So, do I put that data a global variable (and what is
the best way to do that?), or do I have a function
return that value and thus have two invocations but
only one data item, or do I do something else?

What is the rule of thumb?

Other comments on the code are also appreciated :)

#! /bin/zsh

# This file: http://user.it.uu.se/~embe8573/conf/.zsh/dump

dump-vt () {
    local file=$1.png
    local vt=$2
    case $# in
        (1) fbgrab $file              ;;
        (2) sudo fbgrab -c $vt $file
            sudo chown $USER $file    ;;
    esac
}

dump-emacs () { dump-vt $1 1 } # because Emacs runs in tty1

dump-x () {
    local file=$1.png
    local window_name=$2
    local window_id=`wmctrl -l | grep -i $window_name | cut -d " " -f1`
    case $# in
        (1) sleep 10; xwd -root                         ;;
        (2) wmctrl -a $window_name; xwd -id $window_id  ;;
    esac | convert - $file
}

dump () {
    if [[ $DISPLAY ]]; then
        dump-x $@
    else
        dump-vt $@
    fi
}

-- 
underground experts united
http://user.it.uu.se/~embe8573