Rainsbrook

#!/bin/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