【深入理解计算机系统csapp lab】shell lab

最新推荐文章于 2024-01-29 11:19:04 发布

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最新推荐文章于 2024-01-29 11:19:04 发布 · 779 阅读

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CC 4.0 BY-SA版权

本文详细介绍了在深入理解计算机系统（CSAPP）课程中进行的Shell实验室，涵盖了Shell脚本编程、进程创建与通信、文件I/O等核心概念，旨在提升读者对操作系统层面的理解。

/*
 * eval - Evaluate the command line that the user has just typed in
 *
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.  
*/
void eval(char *cmdline)
{
   
   
    char *argv[MAXARGS];
    char buf[MAXLINE];
    int bg;
    pid_t pid;


    sigset_t mask_child,mask_all,prev_all;
    sigfillset(&mask_all);
    sigemptyset(&mask_child);
    sigaddset(&mask_child,SIGCHLD);

    strcpy(buf,cmdline);
    bg=parseline(buf,argv);
    if(argv[0]==NULL)
        return;

    if(!builtin_cmd(argv)){
   
   
	sigprocmask(SIG_BLOCK, &mask_child, &prev_all);
        if((pid=fork())<0){
   
   
            sigprocmask(SIG_SETMASK, &prev_all, NULL);
            fprintf(stderr,"fork error: %s\n",strerror(errno));
            exit(0);
        }
	else if(pid==0){
   
     //child
	    setpgid(0,0);//last hint,很重要！！！
	    sigprocmask(SIG_SETMASK, &prev_all, NULL);
            if(execve(argv[0],argv,environ)<0){
   
   

                printf("%s: Command not found.\n",argv[0]);
                exit(0);		
            }
        }
        //parent
	
	sigprocmask(SIG_BLOCK, &mask_all, NULL);
	addjob(jobs,pid,bg?BG:FG,cmdline);
        sigprocmask(SIG_SETMASK, &prev_all, NULL