#!/bin/bash

# userAudit: print invalid usernames
#! Safe iteration over /etc/passwd using while read -r

awk -F ":" '{print $1}' /etc/passwd | while read -r username; do
    firstChar="${username:0:1}"
    badChar=false

    # Check if username contains only letters
    for ((i=0; i<${#username}; i++)); do
        char="${username:i:1}"
        if ! [[ "$char" =~ [A-Za-z] ]]; then
            badChar=true
            break
        fi
    done

    # Flag invalid usernames
#! Corrected logic to properly flag invalid usernames:
#! check if the firstchar is NOT a letter
    if (( ${#username} > 20 )) || ! [[ "$firstChar" =~ [A-Za-z] ]] || $badChar ; then
#! Quotes around $username in echo for robustness.
        echo "$username"
    fi
done