shell.c

自己实现的简单的shell 自己实现的简单的shell 自己实现的简单的shell

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <fcntl.h>

#define MAXLINE 4096
#define MAXPIPE 16
#define MAXARG 8
#define MAX_IN_CMD 2

struct { 
     char *argv[MAXARG];
     char *in, *out;
} cmd[MAXPIPE+1];

extern int do_cd(char **argv);
extern int do_exit(char **argv);

typedef int (*func_t)(char *argv[]);
struct {
	char *cmd_name;
	func_t handler;
}incmd[MAX_IN_CMD] = {{"cd", do_cd}, {"exit", do_exit}};

int do_cd(char **argv)
{
	return chdir(argv[0]);
}

int do_exit(char **argv)
{
	exit(0);
}

int parse(char *buf, int cmdnum)
{
     int n = 0;
     char *p = buf;

     cmd[cmdnum].in = cmd[cmdnum].out = NULL;
     while (*p != '\0')
     {
          if (*p == ' ')
          {
               *p++ = '\0';
               continue;
          }
          if (*p == '<')
          {
               *p = '\0';
               while (*(++p) == ' ');
               cmd[cmdnum].in = p;
               if (*p++ == '\0')
                    return -1;
               continue;
          }
          if (*p == '>')
          {
               *p = '\0';
               while (*(++p) == ' ');
               cmd[cmdnum].out = p;
               if (*p++ == '\0')
                    return -1;
               continue;
          }
          if (*p != ' ' && ((p == buf) || *(p-1) == '\0'))
          {
               if (n < MAXARG - 1) {
                    cmd[cmdnum].argv[n++] = p++;
                    continue;
               } else
                    return -1;
          }
          p++;
     }
     if (n == 0)
          return -1;
     cmd[cmdnum].argv[n] = NULL;
     return 0;
}

int main(void)
{
     char buf[MAXLINE];
     pid_t pid;
     int fd, i, j, pfd[MAXPIPE][2], pipe_num, cmd_num;
     char* curcmd, *nextcmd;

     while (1) {
		 printf("mysh%% ");
		 if (!fgets(buf, MAXLINE, stdin))
			 exit(0);
		 if (buf[strlen(buf)-1]=='\n')
			 buf[strlen(buf)-1]='\0';
		 cmd_num = 0;
		 nextcmd = buf;
		 while (curcmd = strsep(&nextcmd, "|")) {
			 if (parse(curcmd, cmd_num++)<0) {
				 cmd_num--;
				 break;
			 }
			 if (cmd_num == MAXPIPE + 1)
				 break;
		 }
		 if (!cmd_num)
			 continue;
		 if(cmd_num == 1){
			for(i = 0; i < MAX_IN_CMD; i++){
				if(!strcmp(incmd[i].cmd_name, cmd[0].argv[0])){
					incmd[i].handler(&cmd[i].argv[1]);
					break;
				}
			}
			if(i < MAX_IN_CMD)
				continue;
		 }
		 pipe_num = cmd_num - 1;
				
		 for (i=0; i<pipe_num; i++)
			 if(pipe(pfd[i])){
				 perror("pipe");
				 exit(1);
			   }
		 for (i=0; i<cmd_num; i++)
			 if ((pid=fork())==0)
				 break;
		 if (pid==0) {
			 if (pipe_num) {
				 if (i==0) {
					 dup2(pfd[0][1], STDOUT_FILENO);
					 close(pfd[0][0]);
					 for (j=1; j<pipe_num; j++) {
						 close(pfd[j][0]);
						 close(pfd[j][1]);
					 }
				 } else if (i==pipe_num) {
					 dup2(pfd[i-1][0], STDIN_FILENO);
					 close(pfd[i-1][1]);
					 for (j=0; j<pipe_num-1; j++) {
						 close(pfd[j][0]);
						 close(pfd[j][1]);
					 }
				 } else {
					 dup2(pfd[i-1][0], STDIN_FILENO);
					 close(pfd[i-1][1]);
					 dup2(pfd[i][1], STDOUT_FILENO);
					 close(pfd[i][0]);
					 for (j=0; j<pipe_num; j++) 
						 if (j!=i || j!=i-1) {
					   close(pfd[j][0]);
					   close(pfd[j][1]);
					  }
				 }
			 }
			 if (cmd[i].in) {
				 fd = open(cmd[i].in, O_RDONLY);
				 if (fd != -1)
				 dup2(fd, STDIN_FILENO);
			 }
			 if (cmd[i].out) {
				 fd = open(cmd[i].out, O_WRONLY|O_CREAT|O_TRUNC, 0644);
				 if (fd != -1)
					 dup2(fd, STDOUT_FILENO);
			 }
			 execvp(cmd[i].argv[0], cmd[i].argv);
			 fprintf(stderr, "executing %s error.\n", cmd[i].argv[0]);
			 exit(127);
		 }

		 for (i=0; i<pipe_num; i++) {
			 close(pfd[i][0]);
			 close(pfd[i][1]);
		 }
		 for (i=0; i<cmd_num; i++)
			 wait(NULL);
	 }

	return 0;
}