Not the most elegant:

use warnings;
use strict;

while (<DATA>) {
    chomp;
    if (/[^aeiou][aeiou]p$/i) {
        print "$_ match\n";
    }
    else {
        print "$_ no match\n";
    }
}

__DATA__
carp
step
tip
stoop
steep
asp
food
mop
up
[download]

prints:

carp no match
step match
tip match
stoop no match
steep no match
asp no match
food no match
mop match
up no match
[download]

As you can see, the 2-letter up does not match. Is that ok? UPDATE: I like AR's solution better because it does match for up.