CODEWITHSUNDEEP
javascriptregex
Justin Blank
Justin Blank

Reputation: 1878

Javascript regex with optional groups matches the empty string

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?

Upvotes: 1

Views: 3096

Answers (3)

anubhava
anubhava

Reputation: 784998

As per your comment $$ will always be there. If that's the case then you can simply use:

/\$\$([bBWw]?c?m?\d*)/

Upvotes: 0

mathematical.coffee
mathematical.coffee

Reputation: 56905

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.

Upvotes: 3

hackartist
hackartist

Reputation: 5264

Sure tell it to look for the string inside of the $$ and the space using lookahead and lookbehind.

Upvotes: 0

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