通過分支進程通過管道傳遞變量來執行Shell命令

Question

這是一種無法實現的特殊場景。我想了解我「在做什麼錯誤

情景：
1.叉一個子進程 2.子進程應執行shell命令（例如貓排序文件） 3。外殼命令的參數從父進程通過配管（用於G例如文件輸入。貓排序）

我寫以下程序但它顯示的文件名，而不是打印出文件內容。但它掛着出到屏幕上

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

int main(){ 

    int pipefd[2]; 
    pipe(pipefd); 

    //create a pipe before you fork a child process 
    pid_t cpid = fork(); 
    if(cpid < 0){ 
    perror("Fork"); 
    } 
    else if(cpid == 0){ 
    printf("This is child process\n"); 

    close(pipefd[1]); 
    close(0); 

    dup2(pipefd[0],0); 

    execlp("sort", "sort", NULL); 

    exit(0); 

    } 
    else{ 
    printf("This is parent process\n"); 
    close(pipefd[0]); 

    char *sort_array[] = {"hello", "amigos", "gracias", "hola"}; 
    for (int i=0; i<4; i++){ 
     write(pipefd[1],sort_array[i],strlen(sort_array[i])); 
     write(pipefd[1], "\n",1); 
    } 


    int cstatus; 
    wait(&cstatus); 

    } 


} 

給予任何輸出更新：
原來的例子是無效的。我更新了排序命令。
我想對內容進行排序。但屏幕掛，沒有任何輸出

Answer 1

當您使用dup你模擬子進程stdin與管道的輸入，所以當你執行sort沒有它是從stdin讀取任何參數，它讀取，直到它看到EOF，所以你必須寫信給管然後關閉它。

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

int main(){ 

    int pipefd[2]; 
    //create a pipe before you fork a child process 
    pipe(pipefd); 

    pid_t cpid = fork(); 
    if(cpid < 0){ 
     perror("Fork"); 
    } else if(cpid == 0) { 
     printf("This is child process\n"); 

     close(pipefd[1]); 
     close(0); 

     dup2(pipefd[0],0); 

     execlp("sort", "sort", NULL); 

     exit(0); 

    } else { 
     printf("This is parent process\n"); 
     close(pipefd[0]); 

     char *sort_array[] = {"hello", "amigos", "gracias", "hola"}; 
     for (int i=0; i<4; i++){ 
      write(pipefd[1],sort_array[i],strlen(sort_array[i])); 
      write(pipefd[1], "\n",1); 
     } 
     close(pipefd[1]); 


     int cstatus; 
     wait(&cstatus); 

    } 
} 

Answer 2

pipe(pipefd); // N.B. failed to check the return value, potential error 

//create a pipe before you fork a child process 
pid_t cpid = fork(); 
if (cpid < 0) // `if` is a language keyword, not a function, space after 
{    // opening brace on next line makes reading code easier 
    perror("Fork"); 
} 
else if (cpid == 0) 
{ 
    printf("This is child process\n"); 

    close(pipefd[1]); // closing "write" end of pipe in child 
    close(0);   // closing stdin in child 

    dup2(pipefd[0],0); // returned handle is not stored, see https://linux.die.net/man/3/dup2 

    execlp("cat", "cat", NULL); // function prototype is int execlp(const char *file, const char *arg, ...); 
           // what are you trying to accomplish? 

    exit(0); 
} 
else 
{ 
    printf("This is parent process\n"); 
    close(pipefd[0]); // close "read" end of pipe in parent process 

    write(pipefd[1], "s.txt", 5); // write text into pipe 

    int cstatus; 
    wait(&cstatus); // wait for ??? something 
} 

你在哪裏想到他的名字被傳遞到管道被打開並寫入到輸出文件？