Finding multiple groups in Java regex for simple option parser

Question

I need to modify this regex to find multiple group matches:

(?:--)(?<key>[^\\s=]+)(?:(?<assign> *[ =] *)(?! --)(?<value>"[^"]*"|\\S+))?

In Java:

"(?:--)(?<key>[^\\\\s=]+)(?:(?<assign> *[ =] *)(?! --)(?<value>\\"[^\\"]*\\"|\\\\S+))?"

This matches the following correctly:

• --key=value
• --key=--value
• --key value
• --flag
• --key="--value"
• --key "--value"
• --key=value --foo=bar
• --key=value --foo=bar --flag

But it fails if --flag comes before any other options:

• --key=value --flag --foo=bar

I've been trying to modify the negative lookahead between the assign and value capture groups without success so far. The value captured for flag ends up being --foo=bar instead of null .

Any expert recommendations on how to solve this?

Answer 1

I managed to fix the regex. The website https://regexr.com/ was invaluable.

The fixed regex is:

(?<prefix>--)(?<key>[^\\s=]+)(?:(?! --)(?<assign> *[ =] *)(?! --)(?<value>"[^"]*"|\\S+))?

Here's the Java class and unit test:

https://gist.github.com/kirklund/845baf340a1999a57db9e59e6ba40ce0