my %data =
    map split(/=/, $_, 2),
    grep /^[abc]=/,
    split ' ';

print "$_ is $data{$_}\n"
    for keys %data;
[download]

Or the more flexible:

my %data = /([^=\s]+)=(\S*)/g;

print "$_ is $data{$_}\n"
    for
        grep /^[abc]\z/,
        keys %data;
[download]

Update: Added alternative.