my ($READ, $WRITE);
pipe ($READ, $WRITE);

my $child1 = fork ();
unless ($child1) {
    *STDOUT = $WRITE;
    exec ('cat', $0);
}

my $child2 = fork ();
unless ($child2) {
    *STDIN = $READ;
    exec ('grep', 'grep');
}

waitpid ($child1, 0);
waitpid ($child2, 0);