#!/bin/bash

## This script will find orphaned users in the system that don't
## belong to any groups.

# Call awk to isolate username and group id
awk -F ':' '{print $1, $4}' /etc/passwd |

# Pass that data to the loop
while read user gid ;

# Loop to compare EACH $gid to the entire /etc/group file at once
do
  if grep $gid /etc/group > /dev/null ; # silences grep
  then continue ; # if found, take no action
  else echo "$user does not belong to any known group" ;
  fi
done

## By using awk, a bit of memory is saved because no unused variables
## are declared for the read command.