Here's my take on the problem. It has the advantage, IMHO, of being more easily adaptable to changing requirements because it is more modular.
Notes:
-
The regex uses \x22 in place of " (double-quote) to avoid Windoze command-line escape-ology.
-
A quoted string cannot contain any sort of double-quote, escaped or otherwise.
-
A parenthetic group cannot contain a ')' (right-paren).
(Sorry for the line-wrap.)
>perl -wMstrict -le
"my $s = 'key1=val1 key2=val2 key3=val3 key4=\"val4a val4b\" '
. 'key5=\"val5key=(0 1 2 3)\" key6=(val6a val6b)'
;
;;
my $key = qr{ [[:alpha:]] [[:alnum:]]+ }xms;
my $val = qr{ [[:alpha:]] [[:alnum:]]+ }xms;
my $d_quo = qr{ \x22 [^\x22]* \x22 }xms;
my $paren = qr{ [(] [^)]* [)] }xms;
;;
my $vals = qr{ $val | $d_quo | $paren }xms;
;;
my @opts = $s =~ m{ $key \s* = \s* $vals }xmsg;
;;
print qq{'$s'};
print qq{'$_'} for @opts;
"
'key1=val1 key2=val2 key3=val3 key4="val4a val4b" key5="val5key=(0 1 2
+ 3)" key6=(val6a val6b)'
'key1=val1'
'key2=val2'
'key3=val3'
'key4="val4a val4b"'
'key5="val5key=(0 1 2 3)"'
'key6=(val6a val6b)'
