In such case, you have to know where the end is to determine, where the last `_' is...

I'll assume that the filename ends with .pdf:

if ($filename =~ /^(.*)_(.*)\.pdf$/) {
    # do something with $1 and $2 here
}
[download]

Because of the Perl "longest-first" matching, the underscore will match the last underscore in the filename.

I liked the split method recommended above.
Can you use the OR in the split command to pattern match at the time of the split?

There is a new wrinkle in the mix as well.
There are filenames without "_": 12345.pdf

All comments are welcomed!

I liked the split method recommended above.

Unfortunately it doesn't work with multiple underscores.

If you want to stick with regexp, then try this:

if (/^(.*?)(?:_([^_]*))?\.pdf$/) {
    # do something with $1 and $2
}
[download]

I liked the split method recommended above.

ty

Can you use the OR in the split command to pattern match at the time of the split?

You want the version number to be the last element of the list that split returns, so you could reverse the list, grab the last element, slurp the rest into an array, reverse that array back the right way round again and join the elements with underscores.

There are filenames without "_": 12345.pdf

Yuk, make an @unversioned array and push them into that if you only get one element from split?

#!/usr/bin/perl
use strict;
use warnings;

my @data = qw/12345.pdf
              12345_-v1.pdf  12345_Av1.pdf    
              123456_-v1.pdf 123456_Av1.pdf 123456_Bv1.pdf   
              g05495_1_-v1.pdf 
              zprt0019548_wiper_die-nc_-1.pdf zprt0019548_wiper_die-nc
+_-2.pdf 
              zprt0016809_fg_tooling_A2.pdf   zprt0016809_fg_tooling_A
+3.pdf/;
my %hash;
my @unversioned;

for my $f (sort @data) {
  my ($version,@key) = reverse split /_/,$f;
  my $key = join "_",reverse @key;
  if($key) {
    $hash{$key} = $version;
  }
  else {
    push @unversioned,$version;
  }
}

for my $key (keys %hash) {
  print $key . '_' . $hash{$key} . "\n";
}
print join "\n",@unversioned,q{};
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