Finding duplicate users on CentOS

I’m using the following code to find the duplicate username. However, it gives an error.

#!/bin/bash
cat /etc/passwd | cut -f1 -d":" | /bin/sort -n | /usr/bin/uniq -c |
    while read x; do [ -z "${x}" ] && break set - $x
        if [ $1 -gt 1 ]; then
            uids=`/bin/gawk -F: '($1 == n) { print $3 }' n=$2 
            /etc/passwd | xargs`
            echo "Duplicate User Name ($2): ${uids}"
        fi
    done

I’m facing a syntax error near the token ‘done’ and numeric error. How can I fix this error?

Answer

$ cut -d: -f1 /etc/passwd | sort | uniq -d

This will extract the first field (the usernames) of the :-delimited /etc/passwd-file, sort the result and report any duplicates.

To also get the UID and the rest of the duplicated passwd entries:

cut -d: -f1 /etc/passwd | sort | uniq -d |
while read -r username; do
  grep "^$username:" /etc/passwd
done

To only get the duplicate usernames and their UID:

cut -d: -f1 /etc/passwd | sort | uniq -d |
while read -r username; do
  awk -F: -vu="$username" '$1 == u { print $1, $3 }' /etc/passwd
done

A short note on your script. The syntax looks mostly ok, but you need ; after break and there is a space after both (this may be a cut-and-paste error (now removed by an edit)). Also, I’d avoid giving full paths to standard utilities if there is no good reason for it, and the awk program does not require GNU awk so just awk will do.