What is a word boundary in regex, does \b match hyphen '-'?

regex word-boundary
peter.murray.rust picture peter.murray.rust · Aug 24, 2009 · Viewed 159.2k times · Source

I'm trying to use regexes to match space-separated numbers. I can't find a precise definition of \b ("word boundary"). I had assumed that -12 would be an "integer word" (matched by \b\-?\d+\b) but it appears that this does not work. I'd be grateful to know of ways of .

[I am using Java regexes in Java 1.6]

Example:

Pattern pattern = Pattern.compile("\\s*\\b\\-?\\d+\\s*");
String plus = " 12 ";
System.out.println(""+pattern.matcher(plus).matches());

String minus = " -12 ";
System.out.println(""+pattern.matcher(minus).matches());

pattern = Pattern.compile("\\s*\\-?\\d+\\s*");
System.out.println(""+pattern.matcher(minus).matches());

This returns:

true
false
true

Answer

brianary picture brianary · Aug 24, 2009

A word boundary, in most regex dialects, is a position between \w and \W (non-word char), or at the beginning or end of a string if it begins or ends (respectively) with a word character ([0-9A-Za-z_]).

So, in the string "-12", it would match before the 1 or after the 2. The dash is not a word character.

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