How can I write the regex "All characters are the same"?

Question

I would like it to match:

aaaaaa bb c 

but not:

 aaabaaa cd 

...

Answer 1

Assuming the regex engine supports backlinks,

 ^(.)\1*$ 

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In Java, it will be

 theString.matches("(.)\\1*") 

Answer 2

Using backlinks:

 (.)(\1)* 

Count: match any character followed by the same character 0 or more times.

Depending on the regexp mechanism and your needs, you can bind the regex only to the whole string, not substrings.

Answer 3

If you want to capture what you match, this is ^((.)\2*)$

Answer 4

Just to contribute to this question, you can use BackRefence:

(\ W +) \ S + \ 1

It checks for repeated words separated by spaces.