#!/bin/bash

cut -f3 -d":" /etc/passwd | sort -n | uniq -c | while read x; do
    [ -z "$x" ] && break
    set - $x
    if [ $1 -gt 1 ]; then
        users=$(awk -F: '($3 == n) { print $1 }' n=$2 /etc/passwd | xargs)
        echo "Duplicate UID ($2): $users"
    fi
done
