Get a free port in a Makefile

get_free_port.sh

#!/bin/bash

# Provided by https://superuser.com/a/1293762/622572

comm -23 <(seq 10000 65535) <(ss -tan | awk '{print $4}' | cut -d':' -f2 | grep "[0-9]\{1,5\}" | sort | uniq) | shuf | head -n 1

Makefile

$(eval PORT = $(shell ./get_free_port.sh))

testbidule:
        @echo "I found a free port number : " $(PORT)