i'm able to refine the problem...

Statement of the Problem: parse Medline/Pubmed file paths on a Unix system in order to finally pass the PMID from each path to a pmid2doi conversion website < http://www.pmid2doi.org/ > ... and output companion DOIs…

(1) parse this link and fetch the pmid; "/xxxxx/xxxxx/xxxxx/xxxxx/xxxxx/UNC00000000000042/00223468/v45i3/S0022346809003820";

(2) submit a query to http://www.pmid2doi.org/, fetch the return contents and parse the DOI value.

If you simply point your browser to: http://www.pmid2doi.org/rest/json/doi/18507872

then your browser will display the result in the form: {"pmid":18507872,"doi":"10.1186/gb-2008-9-5-r89"}

and then you need to parse this JSON format.

Examples of how to do that are at: http://beerpla.net/2008/03/27/parsing-json-in-perl-by-example-southparkstudioscom-south-park-episodes/

#!/usr/local/bin/perl

use strict;
use warnings;
use 5.010;
use LWP::Simple;

# Fetch line from <DATA>

while ( <DATA> ) {
    # PMID is an 8-digit string, surrounded by "/" and "/"
    my $pmid = $1 if ( /\/(\d{8})\// );

    # Query pmid in http://www.pmid2doi.org/
    my $ret = get("http://www.pmid2doi.org/rest/json/doi/$pmid");

    unless (defined $ret) {
        warn "Failed to get doi for '$pmid': $!\n";

        next;
    }
     
    # Parse query result, which would be like:
    # {"pmid":18507872,"doi":"10.1186/gb-2008-9-5-r89"}
    if ( $ret =~ /"doi":"(.*?)"}/ ) {
        my $doi = $1;
        # Output
        say $pmid, "\t=>\t", $doi;
    }
    else {
        say "doi not found in '$ret'";
    }
}

exit 0;

__DATA__
/xxxxx/xxxxx/xxxxx/xxxxx/xxxxx/UNC00000000000042/00223468/v45i3/S00223
+46809003820
[download]

i'd appreciate any critiques/insights -- thx!