$x="[x=1 y=3 z=5]";
print join ":", $x=~/(\w+)=(\d+)/g;

##</code><code>##

print join ":", $x=~/\G          # start where prev match left off
                     (?:\A\[)?   # if start of string, expect [
                     (\w+)=(\d+) # our data
                     (?:\s(?!\z) # between pairs, expect \s
                       |\]\z)    # or if end of string, expect ]
                    /gcx;
# if whole string was parsed, pos will be defined and equal to length
print "error" unless pos($x) && pos($x) == length($x);