Yes, I chose $year_left as the name for the variable holding the year number on the left side of the comparison, and $year_right for the right side of the comparison.

You can look at a string and guess if it contains a four digit year by using the following code for example:

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

The regular expression looks at whether the string contains at least one number with four digits that starts with 19 or 20, and sets $year to the first such number. You could put that code into a subroutine as follows to allow for easy reuse:

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

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