shell1.c

模拟Shell的执行过程

#include	<sys/types.h>
#include	<sys/wait.h>
#include	<stdio.h>
#include <unistd.h>
#include <signal.h>

#define MAXLINE 128


int main(void)
{
	char	buf[MAXLINE];
	pid_t	pid;
	int		status;
        sigset_t  newmask_C,oldmask_C,newmask_Z,oldmask_Z,zeromask;
       
        sigemptyset(&zeromask);

        sigemptyset(&newmask_C);
        sigaddset(&newmask_C,SIGINT);

        sigemptyset(&newmask_Z);
        sigaddset(&newmask_Z,SIGTSTP);
        
        
        if(sigprocmask(SIG_BLOCK,&newmask_C,&oldmask_C)<0)
        {
               printf("SIG_BLOCK error\n");
               exit(-1);
        }
       
       
        if(sigprocmask(SIG_BLOCK,&newmask_Z,&oldmask_Z)<0)
        {
               printf("SIG_BLCOK error\n");
               exit(-1);
        } 

	printf("%% ");	/* print prompt (printf requires %% to print %) */
	while (fgets(buf, MAXLINE, stdin) != NULL) {
		buf[strlen(buf) - 1] = 0;/* replace newline with null */
                if(strcmp(buf,"quit")==0)
                   break;
		if ( (pid = fork()) < 0)
			printf("fork error");

		else if (pid == 0) {		/* child */
			execlp(buf, buf, (char *) 0);
			printf("The command %s doesn't exist\n", buf);
			exit(127);
		}

		/* parent */
		if ( (pid = waitpid(pid, &status, 0)) < 0)
			printf("waitpid error");
		printf("%% ");
	}

       if(sigsuspend(&zeromask)!=-1)
       {
              printf("sigsuspend error\n");
              exit(-1);
       }

       if(sigprocmask(SIG_SETMASK,&oldmask_C,NULL)<0)
       {
             printf("SIG_SETMASK error\n");
             exit(-1);
       }
       if(sigprocmask(SIG_SETMASK,&oldmask_Z,NULL)<0)
       {
             printf("SIG_SETMASK error\n");
             exit(-1);
       }
	exit(0);
}