regex - Regular expression to allow spaces between words

Question

I want a regular expression that prevents symbols and only allows letters and numbers. The regex below works great, but it doesn't allow for spaces between words.

^[a-zA-Z0-9_]*$

For example, when using this regular expression "HelloWorld" is fine, but "Hello World" does not match.

How can I tweak it to allow spaces?

Answer 1

tl;dr

Just add a space in your character class.

^[a-zA-Z0-9_ ]*$

 

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Now, if you want to be strict...

The above isn't exactly correct. Due to the fact that * means zero or more, it would match all of the following cases that one would not usually mean to match:

• An empty string, "".
• A string comprised entirely of spaces, "      ".
• A string that leads and / or trails with spaces, "   Hello World  ".
• A string that contains multiple spaces in between words, "Hello   World".

Originally I didn't think such details were worth going into, as OP was asking such a basic question that it seemed strictness wasn't a concern. Now that the question's gained some popularity however, I want to say...

...use @stema's answer.

Which, in my flavor (without using w) translates to:

^[a-zA-Z0-9_]+( [a-zA-Z0-9_]+)*$

(Please upvote @stema regardless.)

Some things to note about this (and @stema's) answer:

• If you want to allow multiple spaces between words (say, if you'd like to allow accidental double-spaces, or if you're working with copy-pasted text from a PDF), then add a + after the space:

  ^w+( +w+)*$
  

• If you want to allow tabs and newlines (whitespace characters), then replace the space with a s+:

  ^w+(s+w+)*$
  

  Here I suggest the + by default because, for example, Windows linebreaks consist of two whitespace characters in sequence, , so you'll need the + to catch both.

Still not working?

Check what dialect of regular expressions you're using.^* In languages like Java you'll have to escape your backslashes, i.e. \w and \s. In older or more basic languages and utilities, like sed, w and s aren't defined, so write them out with character classes, e.g. [a-zA-Z0-9_] and [f p ], respectively.

 

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^{* I know this question is tagged vb.net, but based on 25,000+ views, I'm guessing it's not only those folks who are coming across this question. Currently it's the first hit on google for the search phrase, regular expression space word.}