regex - MongoDB uXXXX issue

Question

In my collection following query returns some result:

db.c.find({t:/a/})

But below query (and any other regex that has uXXXX) returns no result:

db.c.find({t:/u0041/})

What is wrong?

Answer 1

The reason for this is that according to the documentation

MongoDB uses PCRE for regular expressions.

However the PCRE documentation says

The following Perl escape sequences are not supported: l, u, L, U, and N when followed by a character name or Unicode value. (N on its own, matching a non-newline character, is supported.) In fact these are implemented by Perl's general string-handling and are not part of its pattern matching engine. If any of these are encountered by PCRE, an error is generated by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, U and u are interpreted as JavaScript interprets them.

That said, this SO question may be of some help.