Regular Expression

Hello everybody,

With a regular expression, I must scan a line that begins with “user_pref(”.
I began with

Regex r = new Regex("user");

and no problem, it selected the first four characters.
The complication comes with the following one.
Here are a few attempts that failed, if anybody has a better idea …

Regex r1 = new Regex("user_");
Regex r2 = new Regex("user\x5F");
Regex r3 = new Regex("user\x05F");
Regex r4 = new Regex("user\u005F");
Regex r5 = new Regex("user.");
Regex r6 = new Regex("user.{1,1}");

Well, believe it or not, I have worked on that for one hour before asking the question and nothing worked, and as soon as I copied the code back from the forum, all was OK.
So, the question can be reformulated : does anybody has any clue about what happened ?