Look up file type based on extension offered on the command line

use strict;
use warnings;
use Win32::TieRegistry 0.20 (Delimiter=>"/");

sub get_file_association ($) {
   my $x= shift;
   my $reg= $Registry->{"HKEY_CLASSES_ROOT/$x//"}  or return;
   # this usually refers to another entry.
   $reg &&= $Registry->{"HKEY_CLASSES_ROOT/$reg//"} if $x =~ /^\./;
   return $reg;
   }

    
# print get_file_association ('.chm');  example usage (include the dot
+)
foreach (@ARGV) {
   print $_, '=>', (get_file_association($_) || "NOT KNOWN"), "\n";
   }
[download]

Throw-away program to find all extensions for type 'intermediate file'

#!perl -w
use strict;
use Win32::TieRegistry ( FixSzNulls => 1 );

my $Classes= $Registry->{"Classes\\"};
my @keynames= $Classes->SubKeyNames();

my @list0= grep { lc($Classes->{"$_\\"}->GetValue('')) eq 'intermediat
+e file' }  @keynames;
my (@list1, @list2);
foreach (@list0) {
   if (/^\./) {  push @list2, $_; }
   else { push @list1, $_; }
   }
my $matchexp= join ("|", map{"^\Q$_\E\$"}(@list1));
$matchexp= qr($matchexp);

push @list2, grep { /^\./ && lc($Classes->{"$_\\"}->GetValue('')) =~ /
+$matchexp/ } @keynames;

print join ("\n", @list2);
[download]

assoc('.pl', 'd:\perl\bin\perl.exe');
# so you can run programs like this:
run_cmd('c:\stuff\script.pl');
[download]

use vars qw/%extensions/;

# keep known extensions here.
%extensions = ();

sub assoc {
    my ($extension, $prog) = @_;
    $extensions{$extension} = $prog;
}

sub run_cmd {
    my $cmd = shift;
    my $ext = "";

    if ($cmd =~ /(\.\w+)$/) {
       $ext = $1;
    }

    # prepend interpreter for known extension
    if ($ext and exists $extensions{$ext}) {
        $cmd = "$extensions{$ext} $cmd";
    }

    return `$cmd`;
}
[download]

This loose code won't support arguments like myscript.pl --args, but that can be left as an exercise in string parsing.

I hope this is what you were asking!

Update: John M. Dlugosz's response above is probably more what you're looking for, upon reinspection of your question.