Regular Expression to find sequences of lowercase letters joined with underscore

I can't seem to make my regular expression work.

I'd like to have some alpha text, no numbers, an underscore and then some more aplha text.

for example: blah_blah

I have an non-working example here

^[a-z][_][a-z]$

Thanks in advance people.

EDIT: I apologize, I'd like to enforce the use of all 开发者_Go百科lower case.

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^[a-z]+_[a-z]+$

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Try this:

[A-Za-z]+_[A-Za-z]+

Lowercase :

 [a-z]+_[a-z]+

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You just need:

[a-z]+_[a-z]+

or if it needs to be an entire line:

^[a-z]+_[a-z]+$

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Try:

^[a-z]+_[a-z]+$

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Depending on which flavor of regex you're using there are a different possibilities:

^[A-Za-z]+_[A-Za-z]+$
^\a+_\a+$
^[[:alpha:]]+_[[:alpha:]]+$

The first form being the most widely accepted.

Your example suggests you're looking for things exactly like "blah_foo" and don't want to extract it from strings like "Hey blah_foo you". If this is not the case, you should drop the "^" (match the beginning of the string) and "$" (match the end of the string)