my $str = 'this is some text 1989 blah';
my $year;
$year = $1
    if( $str =~ /\b((?:19|20)\d\d)\b/ );

##</code><code>##

sub find_year {
    my( $str ) = @_;
    my $year;
    $year = $1
        if( $str =~ /\b((?:19|20)\d\d)\b/ );
    return $year
}