Practical application of [Linux pipelines and IPC] Pipelines 2

#include  <unistd.h> #include  <stdio.h> #include  <stdlib.h> #include  <sys /types.h> #include  <limits.h> #include  <string.h> #include  <sys/wait.h># include <error.h> #define  DEF_PAGER  "/bin/more"    //defining handler functions #define  maxline  4096   //line maximum number of characters Int main (int argc, char *argv[]) {   int     n;  int     fd[2];  pid_t    pid;  char    *pager, *argv0;  char     line[MAXLINE];  FILE    *fp;  if  (argc != 2 )   //If the parameter is incorrect   {    printf ("Please enter the correct command: <pathname>\n");     exit (1);  }  if  ((Fp = fopen (argv[1],  "R"))  ==  NULL)   //If read-onlyError opening argv[1]   {    printf ("Cannot open file%s",  argv[1]);     Exit (1);  }  if  (pipe (FD)  < 0)   //Create pipeline failure   {  &NBSP;&NBSP;&NBSP;PRINTF ("Create pipe failed \ n");     exit (0);  }  if  (PID  = fork ())  < 0)   //Create child process failed   {    printf (" Create child process failed \ n ");     exit (0);  }  else if  (pid > 0)   {                                //Parent Process      close (Fd[0]);            //Close Read file descriptor      //Argv[1] sent through the pipeline     while  (fgets (LINE,&NBSP;MAXLINE,&NBSP;FP)   != null)      {      n = strlen (line);       if   (Write (fd[1], line, n)  != n)       {         printf ("Write pipeline failed \ n");         exit (1);       }    }    if  (Ferror (FP))    //If the file descriptor is faulted     {        printf ("fgets  Failure \ \ ");         exit (1);    }     close (Fd[1]);   //    if  (Waitpid (pid, NULL, 0)   < 0)     {        printf ("Waitpid failure \ n");         exit (1);     }    exit ( 0);   }  else  //Sub-process   {    close (fd[1]);    if  (fd[ 0] != stdin_fileno)     {      if  (Dup2 (fd[0],  stdin_fileno)  != stdin_fileno)       {         printf ("Dup2 to standard input failed \ n");         exit (1);       }      close (Fd[0]);    /* don ' Parameters of the T need this after dup2 */    }    //exec function     if  ((pager = getenv ("pager")  == null)      {      pager = DEF_PAGER;    }     if  ((ARGV0&NBSP;=&NBSP;STRRCHR (pager,  '/'))  != null)     {       argv0++;    }    else    {       argv0 = pager;    }    if   (Execl (pager, argv0,  (char *) 0)  < 0)     {       printf ("Call Execl failed%s",  pager);       exit (1);     }  }  exit (0);}

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Practical application of [Linux pipelines and IPC] Pipelines 2