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  1. #include <stdio.h>
  2. #include <unistd.h>
  3. #include <sys/types.h>
  4. #include <stdlib.h>
  5.  
  6. void pipeline( char * ar[], int pos, int in_fd);
  7. void error_exit(const char*);
  8. static int child = 0; /* whether it is a child process relative to main() */
  9.  
  10. int main(int argc, char * argv[]) {
  11.   if(argc < 2){
  12.     printf("Usage: %s option (option) ...\n", argv[0]);
  13.     exit(1);
  14.   }
  15.   pipeline(argv, 1, STDIN_FILENO);
  16.   return 0;
  17. }
  18.  
  19. void error_exit(const char *kom){
  20.    perror(kom);
  21.    (child ? _exit : exit)(EXIT_FAILURE);
  22. }
  23.  
  24. void pipeline(char *ar[], int pos, int in_fd){
  25.    if(ar[pos+1] == NULL){ /*last command */
  26.      if(in_fd != STDIN_FILENO){
  27.         if(dup2(in_fd, STDIN_FILENO) != -1)
  28.           close(in_fd); /*successfully redirected*/
  29.         else error_exit("dup2");
  30.      }
  31.      execlp(ar[pos], ar[pos], NULL);
  32.      error_exit("execlp last");
  33.    }
  34.    else{
  35.      int fd[2];
  36.      pid_t childpid;
  37.  
  38.      if ((pipe(fd) == -1) || ((childpid = fork()) == -1)) {
  39.         error_exit("Failed to setup pipeline");
  40.      }
  41.      if (childpid == 0){					/* child executes current command */
  42.         child = 1;
  43.         close(fd[0]);                                  
  44.         if (dup2(in_fd, STDIN_FILENO) == -1)           /*read from in_fd */
  45.            perror("Failed to redirect stdin");         
  46.         if (dup2(fd[1], STDOUT_FILENO) == -1)			/*write to fd[1]*/
  47.            perror("Failed to redirect stdout");
  48.         else if ((close(fd[1]) == -1) || (close(in_fd) == - 1))
  49.            perror("Failed to close extra pipe descriptors");
  50.         else {
  51.            execlp(ar[pos], ar[pos], NULL);
  52.            error_exit("Failed to execlp");
  53.         }
  54.      } 
  55.      close(fd[1]);		/* parent executes the rest of commands */
  56.      close(in_fd);
  57.      pipeline(ar, pos+1, fd[0]);
  58.    }
  59. }
  60.  
  61.  
Runtime error #stdin #stdout 0s 2292KB
comments (?)
stdin
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Standard input is empty
stdout
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Usage: ./prog option (option) ...
https://ideone.com/fedrB8
language:
C (gcc 8.3)
created:
10 years ago
visibility:
secret

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