I would like it to match:
aaaaaa
bb
c
but not:
aaabaaa
cd
...
views:
187answers:
4
+5
A:
Using back references:
(.)(\1)*
Read: match any character followed by that same character 0 or more times.
Depending on the regexp engine and your needs, you might want to anchor the regex to only match the whole string, not substrings.
sepp2k
2010-07-15 18:01:07
Trying Java, but System.out.println("1111111".matches("(.)(\1)*")); prints false
Julio Faerman
2010-07-15 18:12:13
@Julio: You need to double escape in java, i.e. use `\\1` instead of `\1`.
sepp2k
2010-07-15 18:13:44
Great, thanks a lot
Julio Faerman
2010-07-15 18:15:54
+13
A:
Assuming the regex engine supports back-references,
^(.)\1*$
In Java it would be
theString.matches("(.)\\1*")
KennyTM
2010-07-15 18:01:25
Trying java, but System.out.println("1111111".matches("^(.)\1*$")); prints false.
Julio Faerman
2010-07-15 18:11:14
@Kenny: In java `^` and `$` mean beginning and end of line, not string. Also regex matches are anchored by default. So just "(.)\\1*" will work.
sepp2k
2010-07-15 18:17:41
@sepp2k: by default, `^` and `$` match the beginning and end of the String, not line. When the `(?m)` flag is enabled, they match the beginning and end of a line. But when using `String.matches(...)`, `^` and `$` are not needed: by default, `matches(...)` will match the entire input string.
Bart Kiers
2010-07-15 18:53:48
@Bart: The [javadocs for Pattern](http://download.oracle.com/docs/cd/E17476_01/javase/1.5.0/docs/api/java/util/regex/Pattern.html) say "^ The beginning of a line" and "$ The end of a line"
sepp2k
2010-07-15 18:57:34
@sepp2k, well, then the JavaDoc is wrong. Try it yourself: `System.out.println("a\nb".matches("^a$\nb$"));` prints `false`, while `System.out.println("a\nb".matches("(?m)^a$\nb$"));` prints `true`.
Bart Kiers
2010-07-15 19:05:30
@sepp2k, from the JavaDoc as well: *"By default, the regular expressions ^ and $ ignore line terminators and only match at the beginning and the end, respectively, of the entire input sequence."*
Bart Kiers
2010-07-15 19:07:25
@sepp2k, it never occurred to me that `^` and `$` are described as you just mentioned: rather confusing from Sun, err, Oracle! :)
Bart Kiers
2010-07-15 19:14:30
A:
Just for contributing to this question, you can use the BackRefence:
(\w+)\s+\1
It checks repeated words separated by whitespace.
Denis Macedo
2010-07-15 18:49:58