Regular expressions

lighttpd2 uses the “Perl-compatible regular expressions” implementation from GLib, see their Regular expression syntax documentation.

The config format has different ways to provide strings (you can quote with either ' or "; the character used to quote has to be escaped with \ if used inside the string).
The simple (standard) way "text" has the following escape rules:

• "\n" is a newline, "\r" a carriage return, "\t" a tab stop
• "\\" is one \, "\"" is one double quote " and "\'" a single quote '
• escaping single/double quote is optional if the symbol is not used to terminate the string, i.e. '\"' = '"' and "\'" = "'"
• "\xNN": NN must be hexadecimal characters, and the string is replaced with the decoded 8-bit value as a single byte
• All other \ occurences are not removed from the string.

This way is the preferred one for regular expressions; only to actually match a \ you have to do additional escaping ("\\\\"; "\x5C" = "\\" is not working), and \\ is usually not doing what you wanted (matching a digit: "\\d" = "\d"). All other escape rules are compatible with what pcre is doing.

The second way is to place an e before the string like this: e"text". It has the same rules like the normal string, but does not allow unknown escape sequences (the last rule above). To match a digit with pcre this way you’d have to write e"\\d" instead of "\d".