#!/bin/sh
# portfind -- find what is using a port, or find a free port
# Usage: portfind <port>      -- show what's on this port
#        portfind --free      -- find a random free port
#        portfind --free 8000 -- find free port starting from 8000
# Update: need to expand to include a port mapping of --free jumps to first before suggesting random free port. 
if [ "$1" = "--free" ]; then
    start="${2:-3000}"
    port="$start"
    while ss -tlnp "sport = :$port" 2>/dev/null | grep -q LISTEN; do
        port=$((port + 1))
    done
    echo "$port"
else
    port="$1"
    [ -z "$port" ] && { echo "Usage: portfind <port> | portfind --free [start]"; exit 1; }
    echo "=== TCP ==="
    ss -tlnp "sport = :$port" 2>/dev/null
    echo "=== UDP ==="
    ss -ulnp "sport = :$port" 2>/dev/null
fi