$s = q[key1=val1 key2=val2 key3=val3 key4="val4a val4b" key5="val5key=(0 1 2 3)" key6=(val6a val6b)];;

@a = split " (?=key)", $s;;

print for @a;;
key1=val1
key2=val2
key3=val3
key4="val4a val4b"
key5="val5key=(0 1 2 3)"
key6=(val6a val6b)