use Modern::Perl '2014';

my $first  = qr/STRING/;
my $second = qr/MAGIC/;
my $first_pos;
my $second_pos;

while (<DATA>) {
    $first_pos  = $. if /$first/;
    $second_pos = $. if /$second/;
}

if ( $first_pos and $second_pos > $first_pos ) {
    say "Success! STRING at $first_pos followed by MAGIC at $second_pos";
}
else {
    say "Failure! (STRING: $first_pos - MAGIC: $second_pos)";
}

__DATA__
First line
second line
here is the STRING
empty text
the STRING again!
followed by the  MAGIC word
more emptiness
Oh no! the first STRING again
sadness
did we look in vain?
Ah, MAGIC success