const GLib = imports.gi.GLib; let regex = new GLib.Regex(pattern: String, compile_options: GLib.RegexCompileFlags, match_options: GLib.RegexMatchFlags);
The g_regex_*() functions implement regular expression pattern matching using syntax and semantics similar to Perl regular expression.
Some functions accept a @start_position argument, setting it differs from just passing over a shortened string and setting #G_REGEX_MATCH_NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion. For example, consider the pattern "\Biss\B" which finds occurrences of "iss" in the middle of words. ("\B" matches only if the current position in the subject is not a word boundary.) When applied to the string "Mississipi" from the fourth byte, namely "issipi", it does not match, because "\B" is always false at the start of the subject, which is deemed to be a word boundary. However, if the entire string is passed , but with @start_position set to 4, it finds the second occurrence of "iss" because it is able to look behind the starting point to discover that it is preceded by a letter.
Note that, unless you set the #G_REGEX_RAW flag, all the strings passed to these functions must be encoded in UTF-8. The lengths and the positions inside the strings are in bytes and not in characters, so, for instance, "\xc3\xa0" (i.e. "à") is two bytes long but it is treated as a single character. If you set #G_REGEX_RAW the strings can be non-valid UTF-8 strings and a byte is treated as a character, so "\xc3\xa0" is two bytes and two characters long.
When matching a pattern, "\n" matches only against a "\n" character in the string, and "\r" matches only a "\r" character. To match any newline sequence use "\R". This particular group matches either the two-character sequence CR + LF ("\r\n"), or one of the single characters LF (linefeed, U+000A, "\n"), VT vertical tab, U+000B, "\v"), FF (formfeed, U+000C, "\f"), CR (carriage return, U+000D, "\r"), NEL (next line, U+0085), LS (line separator, U+2028), or PS (paragraph separator, U+2029).
The behaviour of the dot, circumflex, and dollar metacharacters are affected by newline characters, the default is to recognize any newline character (the same characters recognized by "\R"). This can be changed with #G_REGEX_NEWLINE_CR, #G_REGEX_NEWLINE_LF and #G_REGEX_NEWLINE_CRLF compile options, and with #G_REGEX_MATCH_NEWLINE_ANY, #G_REGEX_MATCH_NEWLINE_CR, #G_REGEX_MATCH_NEWLINE_LF and #G_REGEX_MATCH_NEWLINE_CRLF match options. These settings are also relevant when compiling a pattern if #G_REGEX_EXTENDED is set, and an unescaped "#" outside a character class is encountered. This indicates a comment that lasts until after the next newline.
Creating and manipulating the samestructure from different threads is not a problem as does not modify its internal state between creation and destruction, on the other hand is not threadsafe.
The regular expressions low-level functionalities are obtained through the excellent [PCRE](http://www.pcre.org/) library written by Philip Hazel.