use strict;
use warnings;

open (FILE, "a.txt");
my $text = "";
while (<FILE>) {
     $text .= $_;
}

close (FILE);

while (my ($one, $two) = extract ($text)) {
     $text = $one . $two;
}

sub extract {
     my ($text) = @_;

     if ($text =~ /(.*?)whatever(.*)/is) {
          return ($1, $2);
     }

     return ();
}