This checks for zero or more of any character followed by 2 occurances of either ?:~.+

The (?: ... ) construction is 'pure grouping.' So (?:~.+){2} matches, but does not assign to a variable, a tilde ~ followed by one or more chars twice.... basically checking for 2 tildes. Somebody else could write this more elegantly, I'm sure.

Here's an example querystring. I'll use the names that shotgunefx suggested.

?item~1~name=boobtube&item~1~qty=1&item~1~code=mysqlpk&item~2~name=loo
+sifer&item~2~qty=1&item~2~code=666&ship~firstname=Han ...
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Since now we're dealing with fields with 2 and 3 ids, we need to adjust the code some.

# Always
use warnings;
use strict;

use CGI;
my $q = CGI::new; 

my %lineitem;
my %ship;

# process params
#
for my $param ( $q->param ) {
    my @id = split(/~/,$param);

    # a SWITCH would work nicely, but I'll try
    # not to confuse the example

    if ( $id[0] eq 'item' ) {
        $lineitem{$id[1]}{$id[2]} = $q->param($param);
    }
    if ( $id[0] eq 'ship' ) {
        $ship{$id[1]} = $q->param($param);
    }
}

# process lineitems
#
print "Please confirm order of<br/> ";
for my $item ( keys %lineitem ) {
    print $lineitem{$item}{qty},
          $lineitem{$item}{name};
    print "<br/>";
}

print "<br/>being shipped to $ship{firstname}<br/>";
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Is this a better example?

(Edit: minor spelling and grammer fixes)
(Edit: replaced my ($id1,$id2,$id3) = with my @id =)