filter_cmd_stdout.go

package main

import (
	"bufio"
	"context"
	"fmt"
	"os"
	"os/exec"
	"os/signal"
	"regexp"
)

func main() {
	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
	defer cancel()

	cmd := exec.CommandContext(ctx, "lsof", "-i", ":443")
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		panic(err)
	}
	err = cmd.Start()
	if err != nil {
		panic(err)
	}
	ex := regexp.MustCompile("->(.*):")
	b := bufio.NewReader(stdout)
	for {
		buf, err := b.ReadBytes('\n')
		if err != nil {
			break
		}
		matches := ex.FindAllSubmatch(buf, -1)
		for _, match := range matches {
			if len(match) == 0 {
				continue
			}
			_, _ = fmt.Fprintf(os.Stdout, "%s\n", match[1])
		}
	}
	err = cmd.Wait()
	if err != nil {
		panic(err)
	}
}