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# dollar-X

    echo -n "Would you like to play a game? "
    read x

    x=`echo $x | sed 's/[^-a-z0-9]//g'`

    if [ -f /usr/games/$x ] ; then
    	tput clear
    	exec /usr/games/$x
    else
    	echo How about a nice game of
    	ls /usr/games
    	exec cat <<QUOTE
    A strange game.
    The only winning move is
    not to play.
    QUOTE
    fi
    exit 0

What's all this dollar-X stuff?

Obviously nothing to do with money.

But look how it's used with /usr/games -- we can speculate that it's the filename it's trying to run as a game.

It's just a noun.

It can change, so it's called a variable.

Lots of languages use dollar signs to indicate variables. (Shells, Perl, PHP.)