use strict;
use warnings;

my $str = "name:val with a :";
my %hash;

$hash{$_->[0]} = $_->[1] for [split /:/, $str, 2];

print map {"$_:$hash{$_}\n"} keys %hash;
[download]

Prints:

name:val with a :
[download]

but I'd not recommend it for production work. The two line variant is a lot less magical.

Note the third parameter to the split though.