#!/usr/bin/env bash
cat /etc/group | cut -f3 -d":" | sort -n | uniq -c | while read x ; do
  [ -z "${x}" ] && break
  set - $x
  if [ $1 -gt 1 ]; then
    groups=`awk -F: '($3 == n) { print $1 }' n=$2 /etc/group | xargs`
    echo "Duplicate GID ($2): ${groups}"
  fi
done
