Regarding your example from the debugger: Your question mark closes the whole construct. After prepending an 'x', the non-capturing parens no longer match at position 0, but since they are optional, they match the empty string - and within that empty string, the first capture is undefined. You can check that by adding the /g modifier to your regex. It should read:

x $foo =~/(?:a=([a-z]+)?)/;

The same would apply to your real pattern, too.

In reply to Re: Making a subpattern optional with ? causes subpattern match to fail. I am confused as to why. by haj
in thread Making a subpattern optional with ? causes subpattern match to fail. I am confused as to why. by msouth

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