Ruby expression

(?:)

It is a valid ruby regular expression, could anyone tell me what it means?

Thanks

From stackoverflow

• It will not capture the part of the matching string in a backreference (i.e \1).

  eric2323223 : @gpojd, How should I understand the '?' and ':' here?

  gpojd : For example, (\d+) will capture consecutive digits in a backreference like \1. If you want to group part of the regex, but do not want to capture them, you would use (?:\d+). Needlessly capturing the data can decrease performance.

• This is an empty, non-capturing group. It has no meaning in this case and can be dropped.

• Like others have said, it's used as the non-capturing syntax for a regex, but, it's also valid ruby syntax outside of a regex.

  In ruby ?: is the integer value for the colon character:

  % irb
  irb> ?:
  => 58
  irb ":"[0]
  => 58
  

  Adding parenthesis doesn't change the value: (?:) == ?:

  When you add spaces (? :), it's the ternary operator, which is essentially shorthand for if/then/else in ruby, so the statement ( bool ? truish : falsy ) is equivalent to

  if bool then 
    truish 
  else 
    falsy 
  end
  

  Chuck : ?: evaluates to '?' in Ruby 1.9.