多管道實施。不工作

Question

我正在爲我的外殼實現多管道。代碼的問題在於它不會將我最後一條命令的輸出打印到我的標準輸出中。有人可以幫忙嗎？ executePipedCommands函數接受指向命令列表頭的指針

我插入例如ls | more | grep s到我的命令列表。

struct cmd_t { 
int nargs, maxargs;  
char **args;   
struct cmd_t *next; 
}; 
typedef struct cmd_t *Cmd; 
void executePipedCommands(Cmd command) { 

    int numPipes = -1; 
    Cmd temp = command; 
    int status; 
    int i = 0; 
    pid_t pid; 

    while(command!= NULL) 
    { 
     numPipes ++; 
     command = command->next; 
    } 
    printf("number of pipes : %d",numPipes); 


    int pipefds[2*numPipes]; 

    for(i = 0; i < (numPipes); i++){ 
     if(pipe(pipefds + i*2) < 0) { 
      perror("couldn't pipe"); 
      exit(EXIT_FAILURE); 
     } 
    } 


    int j = 0; 
    while(command) 
    { 
     pid = fork(); 
     if(pid == 0) 
     { 

      //if not last command 
      if(command->next) 
      { 
       if(dup2(pipefds[j + 1], 1) < 0) 
       { 
        perror("dup2"); 
        exit(EXIT_FAILURE); 
       } 
      } 

      //if not first command&& j!= 2*numPipes 
      if(j != 0) 
      { 
       if(dup2(pipefds[j-2], 0) < 0) 
       { 
        perror(" dup2");///j-2 0 j+1 1 
        exit(EXIT_FAILURE); 

       } 
      } 


      for(i = 0; i < 2*numPipes; i++) 
      { 
        close(pipefds[i]); 
      } 

      if(execvp(*command->args, command->args) < 0) 
      { 
        perror(*command->args); 
        exit(EXIT_FAILURE); 
      } 
     } 
     else if(pid < 0) 
     { 
      perror("error"); 
      exit(EXIT_FAILURE); 
     } 

     command = command->next; 
     j+=2; 
    } 
    /**Parent closes the pipes and wait for children*/ 

    for(i = 0; i < 2 * numPipes; i++){ 
     close(pipefds[i]); 
    } 

    for(i = 0; i < numPipes + 1; i++) 
     wait(&status); 

} 

Answer 1

您的代碼通過鏈表步驟，開始command，當它到達終點，以計算所需管道的數量停止。不幸的是，您不會將列表重新設置爲起點，因此您無法逐步執行列表以執行命令，因爲您已經處於最後。

你大概意思寫：

int numPipes = -1; 
Cmd temp = command; 

while (temp != NULL) 
{ 
    numPipes++; 
    temp = temp->next; 
} 
printf("number of pipes: %d\n", numPipes); 

變量temp是其他未使用。或者你可以寫：

int numPipes = -1; 
Cmd temp = command; 

while (command != NULL) 
{ 
    numPipes++; 
    command = command->next; 
} 
printf("number of pipes: %d\n", numPipes); 

command = temp;