How to use regular expressions with helm-projectile-grep?

Question

I would like to find all strings in files matching the pattern foo_*_bar. I know that one can use \s to match empty characters. What's the pattern for zero or more characters? Could not find it by searching the web.

Answer 1

After some experimentation, I discovered that the following works foo_[[:alnum:]]*_bar. [[:alnum:]] matches alphanumeric characters and * matches the preceding item zero or more times, i.e. without * the string foo__bar does not match the pattern.