How to match repeated patterns?

Question

I would like to match:

some.name.separated.by.dots 

But I don't have any idea how.

I can match a single part like this

 \w+\. 

How can I say "repeat that"

Answer 1

Try the following:

\w+(?:\.\w+)+ 

The + after (?: ... ) tell it to match what is inside the parenthesis one or more times.

Note that \w only matches ASCII characters, so a word like café wouldn't be matches by \w+, let alone words/text containing Unicode.

EDIT

The difference between [...] and (?:...) is that [...] always matches a single character. It is called a "character set" or "character class". So, [abc] does not match the string "abc", but matches one of the characters a, b or c.

The fact that \w+[\.\w+]* also matches your string is because [\.\w+] matches a . or a character from \w, which is then repeated zero or more time by the * after it. But, \w+[\.\w+]* will therefor also match strings like aaaaa or aaa............

The (?:...) is, as I already mentioned, simply used to group characters (and possible repeat those groups).

More info on character sets: http://www.regular-expressions.info/charclass.html

More info on groups: http://www.regular-expressions.info/brackets.html

EDIT II

Here's an example in Java (seeing you post mostly Java answers):

import java.util.regex.Matcher; import java.util.regex.Pattern;  public class Main {     public static void main(String[] args) {         String text = "some.text.here only but not Some other " +                  "there some.name.separated.by.dots and.we are done!";         Pattern p = Pattern.compile("\\w+(?:\\.\\w+)+");         Matcher m = p.matcher(text);         while(m.find()) {             System.out.println(m.group());         }     } } 

which will produce:

some.text.here some.name.separated.by.dots and.we 

Note that m.group(0) and m.group() are equivalent: meaning "the entire match".