regex - capture optional substring -

i'm trying match these lines:

x=1 b c y=5 bb aa x=2 aa ccc d x=3 ccc y=9 d ee ff 

the 'y=x' substring optional. may present in line or not. want capture x=x in group 1, , y=x in optional group 2.

i'm using regular expression:

^(x=[0-9]+?).+?(y=[0-9]+?)?.+?$ 

the whole line matched, i'm capturing first group. second group never captured if optional substring exists. problem between x= , y= lot of different words (with '=' character too).

any ideas how capture optional group 2?

actual example: http://regex101.com/r/rd4so4/1

updated

here's more efficient , cleaner option (that doesn't require alternation):

^(x=[0-9]+)(?:.+?(y=[0-9]+))?.+?$ 

demo

_{note removed lazy repetition [0-9] since shouldn't have issues matching many characters anyways.}

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explanation

the original expression wasn't working because regular expression match left right (and since using lazy repetition, assume understand concept regex "greedy"). though middle .+? lazy, y=[0-9]+ optional continue match way trailing/required .+?$. may not 1 expect, since there lazy repetition..but why stop optional segment when can backtrack , try match again.

mine worked because made middle .+? exist if y=[0-9]+ existed. y=[0-9]+ checked for, if not found okay since whole group still optional. still can end trailing .+?$.

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original

i'm racking brain more concise answer, used alternation make regex engine check y=[0-9]+? before matching everything:

^(x=[0-9]+)(?:.+?(y=[0-9]+).+?|.+?)$ 

demo