1 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <sys/stat.h>
#include <fcntl.h>

void exec(char **args){
    pid_t  pid;
    int status;
    if ((pid = fork()) < 0) {    
    printf("*** ERROR: forking child process failed\n");
    exit(1);
}

else if (pid == 0) {      

    if(execvp(args[0],args)<0)//{
        //printf("argv[0]=%s argv[1]=%s",args[0],args[1]);
        printf("**error in exec\n");
    }

    else {                                  
        while (wait(&status) != pid);
    }
}

void exec2(char **args, char *file){
    printf("file =%s\n",file);
    int fd;
    pid_t pid;
    int status;
    if ((pid = fork()) < 0) {    
printf("*** ERROR: forking child process failed\n");
        exit(1);
    }

    else if (pid == 0) {   
    fd = open(file, O_RDWR | O_CREAT, (mode_t)0600);
    close(1);
    dup2(fd, 1);
    if(execvp(args[0],args)<0){
        printf("**error in exec");
    }

else {  
        printf("\nhere\n");
        close(fd);                                
        while (wait(&status) != pid){
            fflush(stdout) ;
        }
    }
}
    close (fd);
}


void main(){
    char *command;
    char inp[512];
    char *filepath;
    size_t size=0;
    char *substr;
    char *args[512];
    command = (char *) malloc(sizeof(char *) * 512);
    int flag=0;
    int redirect=0;
    int i=0;
    while (1){
        printf("$ ");
        command = fgets(inp, 512/*sizeof(char *)*/, stdin);

        command[strlen(command)-1]='\0';

        if (strchr(command,'>')){
            redirect=1;
            strtok_r(command,">",&filepath);
        }

        size_t siz=4;
        //printf("command=%s\n",command);
        int i=0;
        while(1){
            //printf("i=%d\n",i);
            char *tok = strtok_r(command," ",&substr);
            if (tok==NULL){
                break;
            }
        args[i++] = tok;
/*          printf("tok=%s\n",tok);
            printf("len tok = %d\n",(int)strlen(tok));
            printf("command=%s\n",command);
            printf("substr=%s\n",substr);     
   */           command = substr;
        }

        //printf("args[0]=%s",args[0]);
        if (!strncasecmp(args[0],"exit",siz) || !strncasecmp(args[0],"quit",siz))
        {
            printf("\nBye\n");
            exit(0);
        }

        else if(strcmp(args[0],"cd")==0){
            chdir(args[1]);
            //printf("chdir")   ;
            //system("pwd");
    } 

    else if (redirect==1){
        exec2(args,filepath);
    }

    else exec(args);
}
}

好的，这是我的 shell 代码。当我运行它时，我输入 ls 并给出正确的输出。然后我输入 ls -l 然后再次输入 ls 并给出 ls: cannot access : No such file or directory 同样当我使用 cd 时， ls 不提供输出并且 pwd 说“忽略未使用的参数” ALso cat 不起作用。虽然 mkdir、ps 和 ls -l 有效。

4

1 回答 1

3

不要关闭stdout！

在 之后fork和之前这样做exec：

if (child) {
  int fd = open(file, O_RDWR | O_CREAT, (mode_t)0600);
  close(1);
  dup2(fd, 1);
  if(execvp(args[0],args)<0){
    printf("**error in exec");
  }
}
于 2012-11-12T14:25:54.863 回答