/* Unnamed pipes. */
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>

#define BUFSIZE      2048
#define EVEN_BUFSIZE 1024
#define massert( cond, msg )           \
   if( cond ) {                        \
      perror(msg);                     \
      exit(-1);                        \
   }

#define WC     "/usr/bin/wc"

/*
 * 1. pipe: r & w.
 * 2. fork
 * 3. Parent closes `r`, child closes `w`
 * 4. Parent reads a file and writes even letters.
 * 5. On file end parent sends EOF ( -1 ) and close read descriptor.
 */


int main( int argc, char* argv[] ) {
   
   pid_t chd_pid;
   int pfd[2]; 
   
   massert( pipe(pfd) < 0, "pipe");
   
   chd_pid = fork();
   if( chd_pid > 0 ) {
      /* Parent. */
      int fd, ret;
      char buf[BUFSIZE], even_buf[EVEN_BUFSIZE]; 

      close( pfd[0] );

      /* If no file, read stdin. Bad and not taskcompatible idea? */
      if( argc > 1 ) {
         massert((fd = open( argv[1], O_RDONLY )) < 0, "open");
      } else {
         fd = STDIN_FILENO;
      }

      while(( ret = read( fd, buf, BUFSIZE)) > 0 ) {
         int i, j;
         for( i = 1, j = 0; i < ret; i+=2 ) {
            even_buf[j++] = buf[i];
         }
         write( pfd[1], even_buf, j);
      }
      /* The end of PIPED connection. */
      close( pfd[1] );
      /* Good tone.*/
      close( fd ); /* Don't care of case with stdin? */
      wait( NULL );
   } else if( chd_pid == 0 ) {
      /* Child.*/
      close( pfd[1] );
      massert(dup2( pfd[0], STDIN_FILENO ) < 0, "dup2");
      massert(execl( WC, WC, "--", (char*)0 ) < 0, "execl");
      close(pfd[0]);
      exit(0);      
   } else {
      /* Error. */
      perror("fork");
      _exit(-1);
   } 
   /* Do some clever things. */
   /* Nope. */
   return 0;
}