hi,

If I understand your question, you want to match the line that has HYPHEN towards end of the lines. If so, the below script does that

use warnings;
use strict;

while ( defined( my $line = <DATA> ) ) {
    chomp $line;
    print $line, $/ if  $line =~ m/\-[0-9a-z]{3}/;
}

__DATA__
 DOC_001_123

DOC_002_214

DOC_001-548

DOC_001-987
[download]

Output

DOC_001-548
DOC_001-987
[download]

UPDATE:
You really can see, how your Regex matches, using

use re 'debug';
[download]

in your script or you can get explanation of a regular expression using YAPE::Regex::Explain