port

#!/bin/bash

# Show process info for what's listening on a given port

if [[ $1 == --help ]]; then
    echo "Usage: port [<port>]"
    echo ""
    echo "With no arguments, lists all used ports."
    echo "With a port number, shows the process listening on that port."
    exit 0
fi

if [[ -z $1 ]]; then
    pairs=$(lsof -nP -iTCP -sTCP:LISTEN 2>/dev/null | awk 'NR>1 {
        n = split($(NF-1), a, ":")
        print a[n], $2
    }' | sort -u -k1,1n)
    if [[ -z $pairs ]]; then
        echo "No ports in use"
        exit 0
    fi
    first=true
    while IFS=' ' read -r port pid; do
        if $first; then
            printf "%-7s " "PORT"
            ps -p "$pid" -o pid,user,command 2>/dev/null | head -1
            first=false
        fi
        info=$(ps -p "$pid" -o pid=,user=,command= 2>/dev/null)
        [[ -n $info ]] && printf "%-7s %s\n" "$port" "$info"
    done <<< "$pairs"
    exit 0
fi

port=$1
pids=$(lsof -n -ti ":$port" 2>/dev/null)

if [[ -z $pids ]]; then
    echo "Nothing listening on port $port"
    exit 0
fi

for pid in $pids; do
    ps -p "$pid" -o pid,user,command
done