http://www.perlmonks.org?node_id=192299


in reply to Do nothing? or Do something important in a very obscure way?

/x?/ means match x zero or one times, but prefer 1...
i.e. Match it if you can

/x??/ means match x zero or one times, but prefer 0...
i.e. Match it if you have to

For instance: 

% perl -le '"wxy" =~ /(wx?)/;   print $1'
1:wx
% perl -le '"wxy" =~ /(wx??)/;  print $1'
1:w

% perl -le '"wxy" =~ /(wx?y)/;  print $1'
1:wxy
% perl -le '"wxy" =~ /(wx??y)/; print $1'
1:wxy

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The notation is a little confusing because the two question marks in a row mean different things. /x?/ is really just syntatic sugar for /x{0,1}/. The second question mark turns on min matching. When you look at it this way, the difference between /x{0,1}/ and /x{0,1}?/ should be more clear.

-Blake

In Section Meditations