#!/usr/bin/perl

while (<DATA>)
{
        #($pre, $ranges) = split /=/, $_, 2;
        ($pre, $ranges, $value) = $_ =~ /^(.+?)=([^ ]+) (.+)$/;

        $del = "=";
        @keys = $pre;
        for $mult (split /:/, $ranges)
        {
                @keys = map { $a=$_; map { "$a$del$_" } split /,/, $mult } @keys;
                $del = ':';
        }
        #@hash{@keys} = ('value2') x @keys;
        @hash{@keys} = ($value) x @keys;
}

use Data::Dump 'dd'; dd \%hash;

__DATA__
Prefix1=A,B:c,d value1
Prefix2=A:b,c:1,2 value2
Prefix3=A:*:1,2 value3