Unix shell的輸入重定向不起作用

Question

我發現了同樣的問題，但沒有答案。

在構建我自己的unix shell中，我的輸出重定向工作正常，但是當我嘗試輸入時，它不會執行任何操作。如果你能幫我弄清楚這個問題會很好。 這是我的執行函數代碼：

void execute (char **args) 
{ 
    int pid, status; 
    pid = fork(); 

    if (pid < 0) 
    { 
     perror ("Error forking!"); 
     return; 
    } 


    else if (pid > 0) 
    { 
     fflush(0); 
     while (wait (&status) != pid) 
     continue; 
    } 


    else if (pid == 0) 
    { 

     int i,in=0,out=0; 
     char input[BUF_SIZE],output[BUF_SIZE]; 

     for(i=0;args[i]!=NULL;i++) 
     { 
     if(strcmp(args[i],"<")==0) 
     {   
      args[i]=NULL; 
      strcpy(input,args[i+1]); 
      in=2;   
     }    

     if(strcmp(args[i],">")==0) 
     {  
      args[i]=NULL; 
      strcpy(output,args[i+1]); 
      out=2; 
     }   
     } 


     if(in) 
     { 
     int fd0; 
     if ((fd0 = open(input, O_RDONLY, 0)) < 0) 
     { 
      perror("Couldn't open input file"); 
      exit(0); 
     }   

     dup2(fd0, 0); 

     close(fd0); 
     } 


     if (out) 
     { 
     int fd1; 
     if ((fd1 = creat(output , 0644)) < 0) 
     { 
      perror("Couldn't open the output file"); 
      exit(0); 
     }   

     dup2(fd1, 1); 
     close(fd1); 
     } 

     execvp (*args, args); 
     perror("execvp"); 
     _exit(1); 
    } 

這裏是我的全部代碼：

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

#define ARGSIZE 20 
#define BUF_SIZE 1024 

void execute (char **args); 
void cd (char *directory); 
int killpid (char *pitstr, int sig); 

int main (void) 
{ 
    char line[BUF_SIZE] = {0}; 
    char *args[ARGSIZE] = {NULL}; 
    char *token; 
    int i, argIndex = 0; 

    while (1) 
    { 

     argIndex = 0; 

     for (i = 0; i < ARGSIZE; i++) 
      args[i] = NULL; 

     printf ("shell> "); 

     if (fgets (line, BUF_SIZE, stdin) == NULL) 
     { 
      printf ("EOF received\n"); 
      return 0; 
     } 

     if (*line == '\n') 
     continue; 

     token = strtok (line, " \n"); 

     while (token != NULL) 
     { 
      args[argIndex] = token; 
      token = strtok (NULL, " \n"); 
      argIndex++; 
     } 

     if (!argIndex) 
      continue; 

     if (strcmp (args[0], "quit") == 0 || strcmp (args[0], "exit") == 0) 
      break; 

     if ((strcmp (args[0], "cd") == 0)) 
      cd (args[1]); 
     else if ((strcmp (args[0], "kill") == 0)) 
     { 
      if (args[1]) 
       killpid (args[1], SIGTERM); 
     } 


     else 
      execute (args); 

    } 
    return 0; 
} 

void execute (char **args) 
{ 
    int pid, status; 
    pid = fork(); 

    if (pid < 0) 
    { 
     perror ("Error forking!"); 
     return; 
    } 


    else if (pid > 0) 
    { 
     fflush(0); 
     while (wait (&status) != pid) 
      continue; 
    } 


    else if (pid == 0) 
    { 

     int i,in=0,out=0; 
     char input[BUF_SIZE],output[BUF_SIZE]; 

     for(i=0;args[i]!=NULL;i++) 
     { 
      if(strcmp(args[i],"<")==0) 
      {   
       args[i]=NULL; 
       strcpy(input,args[i+1]); 
       in=2;   
      }    

      if(strcmp(args[i],">")==0) 
      {  
       args[i]=NULL; 
       strcpy(output,args[i+1]); 
       out=2; 
      }   
     } 


     if(in) 
     { 
      int fd0; 
      if ((fd0 = open(input, O_RDONLY, 0)) < 0) 
      { 
       perror("Couldn't open input file"); 
       exit(0); 
      }   

      dup2(fd0, 0); 
      close(fd0); 
     } 


     if (out) 
     { 
      int fd1; 
      if ((fd1 = creat(output , 0644)) < 0) 
      { 
       perror("Couldn't open the output file"); 
       exit(0); 
      }   

      dup2(fd1, 1); 
      close(fd1); 
     } 

     execvp (*args, args); 
     perror("execvp"); 
     _exit(1); 
     } 

} 

void cd (char *directory) 
{ 
    char dir[BUF_SIZE] = {0}; 

    if (!directory) 
    { 
     directory = getenv ("HOME"); 

     if (chdir (directory)) 
      fprintf (stderr, "Failed to enter directory: %s\n", directory); 
     else 
      printf ("%s\n", directory); 

     return; 
    } 

    if (*directory == '~') 
    { 
     strcpy (dir, getenv ("HOME")); 
     strcat (dir, "/"); 
     strcat (dir, directory + 2); 

     if (chdir (dir)) 
      fprintf (stderr, "Failed to enter directory: %s\n", dir); 
     else 
      printf ("%s\n", dir); 

     return; 
    } 

    if (chdir (directory)) 
     fprintf (stderr, "Failed to enter directory: %s\n", directory); 
    else 
     printf ("%s\n", directory); 
} 

int killpid (char *pidstr, int sig) 
{ 
    pid_t pid = (pid_t)atoi (pidstr); 

    if (pid < 1) 
    { 
     fprintf (stderr, "warning: requested pid < 1, ignoring\n"); 
     return (int)pid; 
    } 

    printf (" killing pid '%d' with signal '%d'\n", (int)pid, sig); 
    return 0; 
} 

Answer 1

當你args數組中看到<這裏

if(strcmp(args[i],"<")==0) 

設置ARGS [我]到NULL

args[i]=NULL; 

但是，你把它傳遞給strcmp()

if(strcmp(args[i],">")==0) 

和您的孩子的過程會很樂意段錯誤。使用if-else -construct這裏：

if(strcmp(args[i],"<")==0) {   
    args[i]=NULL; 
    strcpy(input,args[i+1]); 
    in=2;   
} else if(strcmp(args[i],">")==0) {  
    args[i]=NULL; 
    strcpy(output,args[i+1]); 
    out=2; 
} 

這應該修復錯誤。

此外，這可能會派上用場，以檢測這種情況：

... 
while (wait (&status) != pid) 
    continue; 
if (WIFSIGNALED(status)) 
    printf("Killed by signal %d%s\n", 
      WTERMSIG(status), WCOREDUMP(status)?" (Core dumped)":"");