This isn't perl but it's a reasonably comprehensive test for X. You could just go straight to xdpyinfo but then you have to wait for it to time out if no x server is present. It's bash syntax and was provided to me by an instructor on a training course (thanks Boyd!), conversion to perl left as an exercise for the reader :)

declare displayhost=${DISPLAY%:*}
declare pingcmd

case $OSTYPE in
  solaris*) pingcmd="ping $displayhost 1";;
  linux*) pingcmd="ping -c 1 $displayhost";;
  *) : ;;
  # TODO insert other flavors of ping here
esac

# If displayhost is blank DISPLAY is probably ":0" so we 
# shouldn't ping
[[ -z "$displayhost" ]] && pingcmd=""

if ! ( $pingcmd && xdpyinfo ) >/dev/null 2>&1; then
  # Either we can't ping the machine or xdpyinfo failed.
  # Either way, X is probably not going to work!
  unset _running_X
fi
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--
Do not seek to follow in the footsteps of the wise. Seek what they sought. -Basho