#!/usr/bin/perl -w
use strict;

$_ = qq(a "test phrase" +for -"this" +"reg ex");

my (@allkeys, @keys, @keysneed, @keysavoid);

# break string in parts
push @allkeys, $1 while /([+-]?(".*?"|'.*?'|\S*))/g;

# filter accoording to first character
@keys = grep /^[^+-]/, @allkeys;
@keysneed = grep /^\+/, @allkeys;
@keysavoid = grep /^\-/, @allkeys;

# remove + and -
s/^.// for @keysneed, @keysavoid;

# remove bracketing quotes
s/^(["'])(.*)\1$/$2/ for @keysneed, @keysavoid, @keys;

print map "$_\n", '', @keys, '', @keysneed, '', @keysavoid, '';
__END__
OUTPUT:

a
test phrase

for
reg ex

this
[download]

Took a bit of fiddling, I couldn't get it right with ["'] for some reason. :-/

Alternatively, you could always listen to merlyn and refer to CPAN :-)