myshell/cmd_bg.go

package main

import (
	"fmt"
	"os"
	"strconv"
	"syscall"
)

// 后台执行job
func cmd_bg(fields []string, stdin *os.File, stdout *os.File, stderr *os.File) {
	if len(fields) == 1 { // 如果没有指定job，则选编号最小的
		if len(jobs) == 0 { // 如果没有job
			panic("bg: no current job") // 则提示错误
		}

		for i := range jobs {
			fields = append(fields, "%"+strconv.Itoa(i))
			break
		}
	}

	for _, jid := range fields[1:] { // 遍历参数
		id, err := strconv.Atoi(jid[1:]) // 字符串转数字
		if err != nil {
			panic("bg: job not found: " + jid)
		}

		_, ok := jobs[id] // 是否有指定编号的job
		if !ok {
			panic("bg: %" + jid[1:] + ": no such job")
		}

		if jobs[id].state == "running" { // job已经在后台执行
			panic("bg: job already in background")
		}
		jobs[id].state = "running"                             // 修改状态
		jobs[id].cmd.Process.Signal(syscall.SIGCONT)           // 向进程发送SIGCONT信号，继续执行
		os.Setenv("!", strconv.Itoa(jobs[id].cmd.Process.Pid)) // 更新最近一次后台进程的pid
		fmt.Fprintf(stdout, "[%d]    %d continued\t%s\n", id, jobs[id].cmd.Process.Pid, jobs[id].work)
	}
}