Question

I m trying to understand what the following does.

^([^=]+)(?:(?:\\=)(.+))?$

Any ideas?

This is being used here. Obviously it s command line parser but i m trying to understand the syntax so i can actually run the program. This is from commandline-jmxclient , they have no documents on setting JMX properties but in their source code, there is such an option, so i just want to understand how i can invoke that method.

  Matcher m = Client.CMD_LINE_ARGS_PATTERN.matcher(command);
  if ((m == null) || (!m.matches())) {
    throw new ParseException("Failed parse of " + command, 0);
  }

  this.cmd = m.group(1);
  if ((m.group(2) != null) && (m.group(2).length() > 0))
    this.args = m.group(2).split(",");
  else
    this.args = null;

Answer 1

Well the explanation would be this :

"
^           # Assert position at the beginning of the string
(           # Match the regular expression below and capture its match into backreference number 1
   [^=]        # Match any character that is NOT a “=”
      +           # Between one and unlimited times, as many times as possible, giving back as needed (greedy)
)
(?:         # Match the regular expression below
   (?:         # Match the regular expression below
      =           # Match the character “=” literally
   )
   (           # Match the regular expression below and capture its match into backreference number 2
      .           # Match any single character that is not a line break character
         +           # Between one and unlimited times, as many times as possible, giving back as needed (greedy)
   )
)?          # Between zero and one times, as many times as possible, giving back as needed (greedy)
$           # Assert position at the end of the string (or before the line break at the end of the string, if any)
"

It will capture everything before = to backreference 1 and everything after it to backrefrence 2.

e.g.

33333098320498
adhajdh =3232-40923-04924-0924

For the first string everything is capture into $1.

For the second one :

adhajdh  <---------- captured to $1
3232-40923-04924-0924 <----- captured to $2