use strict; # Always
use IO::File; # I like to localize filehandles.

sub CountPatternInFile
{
    my ( $filename, $pattern, $stop_pattern ) = @_;
    my $fh = IO::File->new( $filename ) or die $!;
    my $count = 0;
    while( <$fh> )
    {
        $count += s/($pattern)/$1/g
        last if m/$stop_pattern/;
    }
    close $fh or die $!;
    return $count;
}