regular expressions - same for all languages?

The basics are mostly the same but there are some discrepancies between which engine powers the language, PHP and JavaScript differ since PHP uses PCRE (Perl Compatible Regular Expressions).

PHP also has the POSIX-compatible regex engine (ereg_* functions), but that is deprecated.

If you don't already use it, I suggest you try RegexBuddy. It can convert between several Regex engines.

You can find alternatives for RegexBuddy on Mac here.

You might want to start out by looking here. That's my Bible when I do regexping!

Now, regex should be the same everywhere, at least the fundamentals, however there are cases where it differs from compiler to compiler (or interpreter if you will).

Those could be how you search for a specific pattern, let's take \w as an example, that's: any alphanumeric or underscore character in c# but the pattern in javascript might be different.

When you come to a special case like this, you might want to revise the above provided link.

Regular expression synax varies slightly between languages but for the most part the details are the same. Some regex implementations support slightly different variations on how they process as well as what certain special character sequences mean.

Google is your best friend. Google for regex in the language of your choice.