pipe.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define oops(m, x) {perror(m); exit(x);}

int main(int ac, char **av)
{
    int thepipe[2], newfd, pid;
    if ( ac != 3 ) {
        fprintf(stderr, "useage: pipe cmd1 cmd2\n");
        exit(1);
    }
    if( pipe(thepipe) == -1 )
        oops("Can`t get a pipe", 1);

    if( (pid = fork()) == -1 ) {
        oops("Can`t fork", 2);
    }

    if( pid > 0 ) {
        close(thepipe[1]);

        if( dup2(thepipe[0], 0) == -1 ) 
            oops("could not redirect stdin", 3);
        
        close(thepipe[0]);
        execlp(av[2], av[2], NULL);
        oops(av[2], 4);
    }
    close(thepipe[0]);
    
    if( dup2(thepipe[1], 1) == -1 )
        oops("could not redirect stdout", 4);
    close(thepipe[1]);
    execlp(av[1], av[1], NULL);
    oops(av[1], 5);
}