Regular expression like string == string

What would开发者_如何学Python be regular expression for for example 'aa' to match only 'aa'

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Try this:

^aa$

The ^ and $ are anchors for the start and end of the line. If you have a multiline string you might also want to try:

\Aaa\Z

Which you need depends on what regular expression engine you are using and on whether or not there can be newlines in your string.

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If you want to match any doubled character:

/(.)\1/

If you want to match any repeated character:

/(.)\1+/

If you want to match only repeated letters:

/(\w)\1/

...etc...

If you explain your problem better, we can better help...

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Why would you use a regex for this?

string s = "aa";

bool match = (s == "aa");