How to convert "-?" from Perl Regex to c# regex

Question

I couldn't find any documentation on this symbol. What does "-?" mean when it precedes a parenthetical expression?

Update - The example I saw is the integer and float regex constraints on the WebIDL specification. Here is a direct link to the grammar appendix: http://dev.w3.org/2006/webapi/WebIDL/#idl-grammar

It's an optional -, it is written the same way (meaning the same thing) both regex flavors. — Qtax
– Qtax, Commented Mar 29, 2012 at 7:32

ikegami · Accepted Answer · 2012-03-29 03:00:03Z

3

It's pretty standard for «-?» to mean "match the character «-» zero or one times".

$ perl -E'
   say "$_: ", /^aaa-?bbb\z/ ? "match" : "no match"
      for qw( aaabbb aaa-bbb aaa--bbb );
'
aaabbb: match
aaa-bbb: match
aaa--bbb: no match

I'd be extremely surprised if it didn't work the same way in C#.

answered Mar 29, 2012 at 3:00

ikegami

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3 Comments

smartcaveman Over a year ago

There is similar behavior with a ? in C#. However, the ? has to be a quantifier appearing at the end of a pattern. The Perl context that I saw had the entire pattern prefixed with -?.

smartcaveman Over a year ago

I could see that making sense for the regex, I was looking at (even as a prefix). Do you have any supporting documentation?

Josh Y. Over a year ago

Well, the regexes you linked are supposed to match numbers; numbers may or may not be negative; a negative number starts with a -. So it makes sense to start the pattern with -? to handle that. It's not a "prefix", it's normal regex.

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