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

/* defines for pipe use */
#define READEND  0
#define WRITEEND 1

void copy()
{
	for (;;) {
		char ch;
		if (read( STDIN_FILENO, &ch, 1 ) == 0) break;
		if (ch == ' ') write( STDOUT_FILENO, "_", 1 );
		write( STDOUT_FILENO, &ch, 1 );
	}
}

main()
{
	int mypipe[2];
	pipe( mypipe );
	if (fork()) { /* parent */
		close( mypipe[WRITEEND] );
		dup2( mypipe[READEND], STDIN_FILENO );
		close( mypipe[READEND] );
		copy();
		(void) wait( NULL );
	} else { /* child */
		close( mypipe[READEND] );
		dup2( mypipe[WRITEEND], STDOUT_FILENO );
		close( mypipe[WRITEEND] );
		copy();
		exit( EXIT_SUCCESS );
	}
}