Well, how about this:

sub print_up_to
{
    my( $handle, $string ) = @_;

    while( <$handle> ) {
       last if /$string/o;
       print;
    }
}

use FileHandle;
my $fh = FileHandle->new( 'foo' );
print_up_to( $fh, '^## START' );

## of course, you should be able to do this:
open( FOO, 'foo' );
print_up_to( \*FOO, '^## START' );
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