get next available listening TCP4 port in a range, works with linux netstat and gnu awk

get_port

#!/bin/bash

if [[ $# -ne 2 ]]; then
  echo "Usage: $0 start end"
  exit 1
fi

start=$1
end=$2


# | \ pipes output streaming to the next statement
# ipv4 tcp listening ports and ip's 
netstat -ntl -A inet | \

# strip it just down to the ports
awk -F '[ :]+'  'NR<3 {next} {print $5}' | \

# sort ports numerically
   sort -n | \

# return the first port in the range that's not currently in use
awk -v port=$start -v end=$end '$0<port {next} $0>end {print "port range exhausted"; exit 1} {if ($0==port) {port+=1}} END {print port}'

Can you do me one more favor? Can you make this thing function and an example on how to use it? Thanks so much.