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/ );
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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
}
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Ok, I've been trying to break things down with the info you have provided, intially with a simpler problem so I can work out whats going on. I'm trying to print the year from the title in a file called csv3 (which contains 1989 in the title) using the following code but it isn't printing anything, what am I doing wrong?

 #!/bin/perl

open CSV3, "<csv3" or die;

while (<CSV3>) {

  chomp;

my ($title) = $_ =~ /^.+?,\s*([^,]+?),/; #/ match the title         

    my %words;

    $words{$_}++ for split /\s+/, $title;    #/ get words             

    ## Collect unique words                                           
    #+                                             
    #    my @titlewords = keys(%words);                               
+           
my @titlewords = keys(%words);
#print "$title"


}



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

&find_year ($title);
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I would have thought the   &find_year ($title); would have taken the title and applied the subroutine to this string, picking out the 1989?

You call find_year(), but you never print its output. For testing, you could start with:

for my $title (
    "Let's party like it's 1999",
    "If 6 was 9",
    "If 6 was 9",
    "Summer of 69",
    "Disco 2000",
) {
    print $title , " => ", find_year($title), "\n";
}
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The code as posted doesn't contain an (uncommented) print or other output statement - so, what should it print?