GLib.Regex¶

record (struct)

A GRegex is a compiled form of a regular expression.

After instantiating a GRegex, you can use its methods to find matches in a string, replace matches within a string, or split the string at matches.

GRegex implements regular expression pattern matching using syntax and semantics (such as character classes, quantifiers, and capture groups) similar to Perl regular expression. See the PCRE documentation for details.

A typical scenario for regex pattern matching is to check if a string matches a pattern. The following statements implement this scenario.

const char *regex_pattern = ".*GLib.*";
const char *string_to_search = "You will love the GLib implementation of regex";
g_autoptr(GMatchInfo) match_info = NULL;
g_autoptr(GRegex) regex = NULL;

regex = g_regex_new (regex_pattern, G_REGEX_DEFAULT, G_REGEX_MATCH_DEFAULT, NULL);
g_assert (regex != NULL);

if (g_regex_match (regex, string_to_search, G_REGEX_MATCH_DEFAULT, &match_info))
  {
    int start_pos, end_pos;
    g_match_info_fetch_pos (match_info, 0, &start_pos, &end_pos);
    g_print ("Match successful! Overall pattern matches bytes %d to %d\n", start_pos, end_pos);
  }
else
  {
    g_print ("No match!\n");
  }

The constructor for GRegex includes two sets of bitmapped flags:

RegexCompileFlags—These flags control how GLib compiles the regex. There are options for case sensitivity, multiline, ignoring whitespace, etc.
RegexMatchFlags—These flags control GRegex’s matching behavior, such as anchoring and customizing definitions for newline characters.

Some regex patterns include backslash assertions, such as \d (digit) or \D (non-digit). The regex pattern must escape those backslashes. For example, the pattern "\\d\\D" matches a digit followed by a non-digit.

GLib’s implementation of pattern matching includes a start_position argument for some of the match, replace, and split methods. Specifying a start position provides flexibility when you want to ignore the first n characters of a string, but want to incorporate backslash assertions at character n - 1. For example, a database field contains inconsistent spelling for a job title: healthcare provider and health-care provider. The database manager wants to make the spelling consistent by adding a hyphen when it is missing. The following regex pattern tests for the string care preceded by a non-word boundary character (instead of a hyphen) and followed by a space.

const char *regex_pattern = "\\Bcare\\s";

An efficient way to match with this pattern is to start examining at start_position 6 in the string healthcare or health-care.

const char *regex_pattern = "\\Bcare\\s";
const char *string_to_search = "healthcare provider";
g_autoptr(GMatchInfo) match_info = NULL;
g_autoptr(GRegex) regex = NULL;

regex = g_regex_new (
  regex_pattern,
  G_REGEX_DEFAULT,
  G_REGEX_MATCH_DEFAULT,
  NULL);
g_assert (regex != NULL);

g_regex_match_full (
  regex,
  string_to_search,
  -1,
  6, // position of 'c' in the test string.
  G_REGEX_MATCH_DEFAULT,
  &match_info,
  NULL);

The method Regex.match_full (and other methods implementing start_pos) allow for lookback before the start position to determine if the previous character satisfies an assertion.

Unless you set the RegexCompileFlags.RAW as one of the GRegexCompileFlags, all the strings passed to GRegex methods 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.

Regarding line endings, \n matches a \n character, and \r matches a \r character. More generally, \R matches all typical line endings: CR + LF (\r\n), 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), and PS (paragraph separator, U+2029).

The behaviour of the dot, circumflex, and dollar metacharacters are affected by newline characters. By default, GRegex matches any newline character matched by \R. You can limit the matched newline characters by specifying the RegexMatchFlags.NEWLINE_CR, RegexMatchFlags.NEWLINE_LF, and RegexMatchFlags.NEWLINE_CRLF compile options, and with RegexMatchFlags.NEWLINE_ANY, RegexMatchFlags.NEWLINE_CR, RegexMatchFlags.NEWLINE_LF and RegexMatchFlags.NEWLINE_CRLF match options. These settings are also relevant when compiling a pattern if RegexCompileFlags.EXTENDED is set and an unescaped # outside a character class is encountered. This indicates a comment that lasts until after the next newline.

Because GRegex does not modify its internal state between creation and destruction, you can create and modify the same GRegex instance from different threads. In contrast, MatchInfo is not thread safe.

The regular expression low-level functionalities are obtained through the excellent PCRE library written by Philip Hazel.

Constructors¶

new¶

@classmethod
def new(cls, pattern: str, compile_options: RegexCompileFlags | int, match_options: RegexMatchFlags | int) -> Regex | None

Compiles the regular expression to an internal form, and does the initial setup of the Regex structure.

Parameters:

pattern — the regular expression
compile_options — compile options for the regular expression, or 0
match_options — match options for the regular expression, or 0

Methods¶

get_capture_count¶

def get_capture_count(self) -> int

Returns the number of capturing subpatterns in the pattern.

get_compile_flags¶

def get_compile_flags(self) -> RegexCompileFlags

Returns the compile options that regex was created with.

Depending on the version of PCRE that is used, this may or may not include flags set by option expressions such as (?i) found at the top-level within the compiled pattern.

get_has_cr_or_lf¶

def get_has_cr_or_lf(self) -> bool

Checks whether the pattern contains explicit CR or LF references.

get_match_flags¶

def get_match_flags(self) -> RegexMatchFlags

Returns the match options that regex was created with.

get_max_backref¶

def get_max_backref(self) -> int

Returns the number of the highest back reference in the pattern, or 0 if the pattern does not contain back references.

get_max_lookbehind¶

def get_max_lookbehind(self) -> int

Gets the number of characters in the longest lookbehind assertion in the pattern. This information is useful when doing multi-segment matching using the partial matching facilities.

get_pattern¶

def get_pattern(self) -> str

Gets the pattern string associated with regex, i.e. a copy of the string passed to Regex.new.

get_string_number¶

def get_string_number(self, name: str) -> int

Retrieves the number of the subexpression named name.

Parameters:

name — name of the subexpression

match_¶

def match_(self, string: str, match_options: RegexMatchFlags | int) -> tuple[bool, MatchInfo]

Scans for a match in string for the pattern in regex. The match_options are combined with the match options specified when the regex structure was created, letting you have more flexibility in reusing Regex structures.

Unless RegexCompileFlags.RAW is specified in the options, string must be valid UTF-8.

A MatchInfo structure, used to get information on the match, is stored in match_info if not None. Note that if match_info is not None then it is created even if the function returns False, i.e. you must free it regardless if regular expression actually matched.

To retrieve all the non-overlapping matches of the pattern in string you can use MatchInfo.next.

static void
print_uppercase_words (const gchar *string)
{
  // Print all uppercase-only words.
  GRegex *regex;
  GMatchInfo *match_info;

  regex = g_regex_new ("[A-Z]+", G_REGEX_DEFAULT, G_REGEX_MATCH_DEFAULT, NULL);
  g_regex_match (regex, string, 0, &match_info);
  while (g_match_info_matches (match_info))
    {
      gchar *word = g_match_info_fetch (match_info, 0);
      g_print ("Found: %s\n", word);
      g_free (word);
      g_match_info_next (match_info, NULL);
    }
  g_match_info_free (match_info);
  g_regex_unref (regex);
}

string is not copied and is used in MatchInfo internally. If you use any MatchInfo method (except MatchInfo.free) after freeing or modifying string then the behaviour is undefined.

Parameters:

string — the string to scan for matches
match_options — match options

match_all¶

def match_all(self, string: str, match_options: RegexMatchFlags | int) -> tuple[bool, MatchInfo]

Using the standard algorithm for regular expression matching only the longest match in the string is retrieved. This function uses a different algorithm so it can retrieve all the possible matches. For more documentation see Regex.match_all_full.

A MatchInfo structure, used to get information on the match, is stored in match_info if not None. Note that if match_info is not None then it is created even if the function returns False, i.e. you must free it regardless if regular expression actually matched.

string is not copied and is used in MatchInfo internally. If you use any MatchInfo method (except MatchInfo.free) after freeing or modifying string then the behaviour is undefined.

Parameters:

string — the string to scan for matches
match_options — match options

match_all_full¶

def match_all_full(self, string: list[str], start_position: int, match_options: RegexMatchFlags | int) -> tuple[bool, MatchInfo]

Using the standard algorithm for regular expression matching only the longest match in the string is retrieved, it is not possible to obtain all the available matches. For instance matching "<a> <c>" against the pattern "<.*>" you get "<a> <c>".

This function uses a different algorithm (called DFA, i.e. deterministic finite automaton), so it can retrieve all the possible matches, all starting at the same point in the string. For instance matching "<a> <c>" against the pattern "<.*>" you would obtain three matches: "<a> <c>", "<a> " and "<a>".

The number of matched strings is retrieved using MatchInfo.get_match_count. To obtain the matched strings and their position you can use, respectively, MatchInfo.fetch and MatchInfo.fetch_pos. Note that the strings are returned in reverse order of length; that is, the longest matching string is given first.

Note that the DFA algorithm is slower than the standard one and it is not able to capture substrings, so backreferences do not work.

Setting start_position differs from just passing over a shortened string and setting RegexMatchFlags.NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion, such as "\b".

Unless RegexCompileFlags.RAW is specified in the options, string must be valid UTF-8.

A MatchInfo structure, used to get information on the match, is stored in match_info if not None. Note that if match_info is not None then it is created even if the function returns False, i.e. you must free it regardless if regular expression actually matched.

string is not copied and is used in MatchInfo internally. If you use any MatchInfo method (except MatchInfo.free) after freeing or modifying string then the behaviour is undefined.

Parameters:

string — the string to scan for matches
start_position — starting index of the string to match, in bytes
match_options — match options

match_full¶

def match_full(self, string: list[str], start_position: int, match_options: RegexMatchFlags | int) -> tuple[bool, MatchInfo]

Scans for a match in string for the pattern in regex. The match_options are combined with the match options specified when the regex structure was created, letting you have more flexibility in reusing Regex structures.

Setting start_position differs from just passing over a shortened string and setting RegexMatchFlags.NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion, such as "\b".

Unless RegexCompileFlags.RAW is specified in the options, string must be valid UTF-8.

A MatchInfo structure, used to get information on the match, is stored in match_info if not None. Note that if match_info is not None then it is created even if the function returns False, i.e. you must free it regardless if regular expression actually matched.

string is not copied and is used in MatchInfo internally. If you use any MatchInfo method (except MatchInfo.free) after freeing or modifying string then the behaviour is undefined.

To retrieve all the non-overlapping matches of the pattern in string you can use MatchInfo.next.

static void
print_uppercase_words (const gchar *string)
{
  // Print all uppercase-only words.
  GRegex *regex;
  GMatchInfo *match_info;
  GError *error = NULL;

  regex = g_regex_new ("[A-Z]+", G_REGEX_DEFAULT, G_REGEX_MATCH_DEFAULT, NULL);
  g_regex_match_full (regex, string, -1, 0, 0, &match_info, &error);
  while (g_match_info_matches (match_info))
    {
      gchar *word = g_match_info_fetch (match_info, 0);
      g_print ("Found: %s\n", word);
      g_free (word);
      g_match_info_next (match_info, &error);
    }
  g_match_info_free (match_info);
  g_regex_unref (regex);
  if (error != NULL)
    {
      g_printerr ("Error while matching: %s\n", error->message);
      g_error_free (error);
    }
}

Parameters:

string — the string to scan for matches
start_position — starting index of the string to match, in bytes
match_options — match options

ref¶

def ref(self) -> Regex

Increases reference count of regex by 1.

replace¶

def replace(self, string: list[str], start_position: int, replacement: str, match_options: RegexMatchFlags | int) -> str

Replaces all occurrences of the pattern in regex with the replacement text. Backreferences of the form \number or \g<number> in the replacement text are interpolated by the number-th captured subexpression of the match, \g<name> refers to the captured subexpression with the given name. \0 refers to the complete match, but \0 followed by a number is the octal representation of a character. To include a literal \ in the replacement, write \\\\.

There are also escapes that changes the case of the following text:

\l: Convert to lower case the next character
\u: Convert to upper case the next character
\L: Convert to lower case till \E
\U: Convert to upper case till \E
\E: End case modification

If you do not need to use backreferences use Regex.replace_literal.

The replacement string must be UTF-8 encoded even if RegexCompileFlags.RAW was passed to Regex.new. If you want to use not UTF-8 encoded strings you can use Regex.replace_literal.

Setting start_position differs from just passing over a shortened string and setting RegexMatchFlags.NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion, such as "\b".

Parameters:

string — the string to perform matches against
start_position — starting index of the string to match, in bytes
replacement — text to replace each match with
match_options — options for the match

replace_eval¶

def replace_eval(self, string: list[str], start_position: int, match_options: RegexMatchFlags | int, eval: RegexEvalCallback) -> str

Replaces occurrences of the pattern in regex with the output of eval for that occurrence.

Setting start_position differs from just passing over a shortened string and setting RegexMatchFlags.NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion, such as "\b".

The following example uses Regex.replace_eval to replace multiple strings at once:

static gboolean
eval_cb (const GMatchInfo *info,
         GString          *res,
         gpointer          data)
{
  gchar *match;
  gchar *r;

   match = g_match_info_fetch (info, 0);
   r = g_hash_table_lookup ((GHashTable *)data, match);
   g_string_append (res, r);
   g_free (match);

   return FALSE;
}

...

GRegex *reg;
GHashTable *h;
gchar *res;

h = g_hash_table_new (g_str_hash, g_str_equal);

g_hash_table_insert (h, "1", "ONE");
g_hash_table_insert (h, "2", "TWO");
g_hash_table_insert (h, "3", "THREE");
g_hash_table_insert (h, "4", "FOUR");

reg = g_regex_new ("1|2|3|4", G_REGEX_DEFAULT, G_REGEX_MATCH_DEFAULT, NULL);
res = g_regex_replace_eval (reg, text, -1, 0, 0, eval_cb, h, NULL);
g_hash_table_destroy (h);

...

Parameters:

string — string to perform matches against
start_position — starting index of the string to match, in bytes
match_options — options for the match
eval — a function to call for each match

replace_literal¶

def replace_literal(self, string: list[str], start_position: int, replacement: str, match_options: RegexMatchFlags | int) -> str

Replaces all occurrences of the pattern in regex with the replacement text. replacement is replaced literally, to include backreferences use Regex.replace.

Setting start_position differs from just passing over a shortened string and setting RegexMatchFlags.NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion, such as "\b".

Parameters:

string — the string to perform matches against
start_position — starting index of the string to match, in bytes
replacement — text to replace each match with
match_options — options for the match

split¶

def split(self, string: str, match_options: RegexMatchFlags | int) -> list[str]

Breaks the string on the pattern, and returns an array of the tokens. If the pattern contains capturing parentheses, then the text for each of the substrings will also be returned. If the pattern does not match anywhere in the string, then the whole string is returned as the first token.

As a special case, the result of splitting the empty string "" is an empty vector, not a vector containing a single string. The reason for this special case is that being able to represent an empty vector is typically more useful than consistent handling of empty elements. If you do need to represent empty elements, you'll need to check for the empty string before calling this function.

A pattern that can match empty strings splits string into separate characters wherever it matches the empty string between characters. For example splitting "ab c" using as a separator "\s*", you will get "a", "b" and "c".

Parameters:

string — the string to split with the pattern
match_options — match time option flags

split_full¶

def split_full(self, string: list[str], start_position: int, match_options: RegexMatchFlags | int, max_tokens: int) -> list[str]

Breaks the string on the pattern, and returns an array of the tokens. If the pattern contains capturing parentheses, then the text for each of the substrings will also be returned. If the pattern does not match anywhere in the string, then the whole string is returned as the first token.

As a special case, the result of splitting the empty string "" is an empty vector, not a vector containing a single string. The reason for this special case is that being able to represent an empty vector is typically more useful than consistent handling of empty elements. If you do need to represent empty elements, you'll need to check for the empty string before calling this function.

A pattern that can match empty strings splits string into separate characters wherever it matches the empty string between characters. For example splitting "ab c" using as a separator "\s*", you will get "a", "b" and "c".

Setting start_position differs from just passing over a shortened string and setting RegexMatchFlags.NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion, such as "\b".

Parameters:

string — the string to split with the pattern
start_position — starting index of the string to match, in bytes
match_options — match time option flags
max_tokens — the maximum number of tokens to split string into. If this is less than 1, the string is split completely

unref¶

def unref(self) -> None

Decreases reference count of regex by 1. When reference count drops to zero, it frees all the memory associated with the regex structure.

Static functions¶

check_replacement¶

@staticmethod
def check_replacement(replacement: str) -> tuple[bool, bool]

Checks whether replacement is a valid replacement string (see Regex.replace), i.e. that all escape sequences in it are valid.

If has_references is not None then replacement is checked for pattern references. For instance, replacement text 'foo\n' does not contain references and may be evaluated without information about actual match, but '\0\1' (whole match followed by first subpattern) requires valid MatchInfo object.

Parameters:

replacement — the replacement string

error_quark¶

@staticmethod
def error_quark() -> Quark

escape_nul¶

@staticmethod
def escape_nul(string: str, length: int) -> str

Escapes the nul characters in string to "\x00". It can be used to compile a regex with embedded nul characters.

For completeness, length can be -1 for a nul-terminated string. In this case the output string will be of course equal to string.

Parameters:

string — the string to escape
length — the length of string

escape_string¶

@staticmethod
def escape_string(string: str, length: int) -> str

Escapes the special characters used for regular expressions in string, for instance "a.b*c" becomes "a.b*c". This function is useful to dynamically generate regular expressions.

string can contain nul characters that are replaced with "\0", in this case remember to specify the correct length of string in length.

Parameters:

string — the string to escape
length — the length of string, in bytes, or -1 if string is nul-terminated

match_simple¶

@staticmethod
def match_simple(pattern: str, string: str, compile_options: RegexCompileFlags | int, match_options: RegexMatchFlags | int) -> bool

Scans for a match in string for pattern.

This function is equivalent to Regex.match_ but it does not require to compile the pattern with Regex.new, avoiding some lines of code when you need just to do a match without extracting substrings, capture counts, and so on.

If this function is to be called on the same pattern more than once, it's more efficient to compile the pattern once with Regex.new and then use Regex.match_.

Parameters:

pattern — the regular expression
string — the string to scan for matches
compile_options — compile options for the regular expression, or 0
match_options — match options, or 0

split_simple¶

@staticmethod
def split_simple(pattern: str, string: str, compile_options: RegexCompileFlags | int, match_options: RegexMatchFlags | int) -> list[str]

Breaks the string on the pattern, and returns an array of the tokens. If the pattern contains capturing parentheses, then the text for each of the substrings will also be returned. If the pattern does not match anywhere in the string, then the whole string is returned as the first token.

This function is equivalent to Regex.split but it does not require to compile the pattern with Regex.new, avoiding some lines of code when you need just to do a split without extracting substrings, capture counts, and so on.

If this function is to be called on the same pattern more than once, it's more efficient to compile the pattern once with Regex.new and then use Regex.split.

As a special case, the result of splitting the empty string "" is an empty vector, not a vector containing a single string. The reason for this special case is that being able to represent an empty vector is typically more useful than consistent handling of empty elements. If you do need to represent empty elements, you'll need to check for the empty string before calling this function.

A pattern that can match empty strings splits string into separate characters wherever it matches the empty string between characters. For example splitting "ab c" using as a separator "\s*", you will get "a", "b" and "c".

Parameters:

pattern — the regular expression
string — the string to scan for matches
compile_options — compile options for the regular expression, or 0
match_options — match options, or 0