Something

#!/bin/bash

echo "This script will create a player account for you"
echo "Please enter your desired username or press control-C to abort"

NAME=""
USERS=`wc -l /etc/passwd`

if (( $USERS < 28 )); then
    until [ ! $NAME == "" ]; do
            read NAME
            id "$NAME" > /dev/null 2>&1 && echo "Username already taken, choose another one." && NAME=""
    done
    
    /var/lib/adom/server/adom_adduser.sh "$NAME"

else
    echo "Sorry, user limit reached. No new users may be created"
    sleep 3
fi