Question

I’m trying to take a string that looks something like

"[go]$$Bcm11 Prisoners:"

and match the Bcm11 portion. Every single portion of it is optional (except technically, if the m appears, the , so I’m using the regex:

/([bBWw])?(c?)m?([0-9]*)/

Unfortunately, this cheerfully matches the empty string. Removing a ‘?’ or ‘*’ gets the right behavior, but makes that component non-optional.

Is there any way to force this regex to match a non-empty string when it’s available?

Answer 1

Use a lookahead (?=...) to make sure there’s something in the string.
This makes sure that at least one of your allowable characters is present.

/(?=[BbWwcm0-9])([bBWw])?(c?)m?([0-9]*)/

The performance would be much improved, however, if you could add a ^, $, or even \b to your regex. For example,

/\b(?=[BbWwcm0-9])([bBWw])?(c?)m?([0-9]*)\b/

which makes sure your match at least grabs the entire word and not just (say) the B.