How can i write the regex “All characters are the same”?

问题

I would like it to match:

aaaaaa
bb
c

but not:

aaabaaa
cd

...

回答1:

Assuming the regex engine supports back-references,

^(.)\1*$

---

In Java it would be

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

回答2:

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.

回答3:

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

回答4:

Just for contributing to this question, you can use the BackRefence:

(\w+)\s+\1

It checks repeated words separated by whitespace.

来源：https://stackoverflow.com/questions/3258444/how-can-i-write-the-regex-all-characters-are-the-same