# Struct regex::Regex [−] [src]

    pub struct Regex(_);

A compiled regular expression for matching Unicode strings.

It is represented as either a sequence of bytecode instructions (dynamic) or as a specialized Rust function (native). It can be used to search, split or replace text. All searching is done with an implicit `.*?` at the beginning and end of an expression. To force an expression to match the whole string (or a prefix or a suffix), you must use an anchor like `^` or `$` (or `\A` and `\z`).

While this crate will handle Unicode strings (whether in the regular expression or in the search text), all positions returned are byte indices. Every byte index is guaranteed to be at a Unicode code point boundary.

The lifetimes `'r` and `'t` in this crate correspond to the lifetime of a compiled regular expression and text to search, respectively.

The only methods that allocate new strings are the string replacement methods. All other methods (searching and splitting) return borrowed pointers into the string given.

# Examples

Find the location of a US phone number:

    let re = Regex::new("[0-9]{3}-[0-9]{3}-[0-9]{4}").unwrap();
    assert_eq!(re.find("phone: 111-222-3333"), Some((7, 19)));

# Using the `std::str::StrExt` methods with `Regex`

> Note: This section requires that this crate is currently compiled with the `pattern` Cargo feature enabled.

Since `Regex` implements `Pattern`, you can use regexes with methods defined on `std::str::StrExt`. For example, `is_match`, `find`, `find_iter` and `split` can be replaced with `StrExt::contains`, `StrExt::find`, `StrExt::match_indices` and `StrExt::split`.

Here are some examples:

    let re = Regex::new(r"\d+").unwrap();
    let haystack = "a111b222c";

    assert!(haystack.contains(&re));
    assert_eq!(haystack.find(&re), Some(1));
    assert_eq!(haystack.match_indices(&re).collect::<Vec<_>>(),
               vec![(1, 4), (5, 8)]);
    assert_eq!(haystack.split(&re).collect::<Vec<_>>(), vec!["a", "b", "c"]);

## Methods

### `impl Regex`

#### `fn new(re: &str) -> Result<Regex, Error>`

Compiles a regular expression. Once compiled, it can be used repeatedly to search, split or replace text in a string.

If an invalid expression is given, then an error is returned.

#### `fn with_size_limit(size: usize, re: &str) -> Result<Regex, Error>`

Compiles a regular expression with the given size limit.

The size limit is applied to the size of the compiled data structure. If the data structure exceeds the size given, then an error is returned.

#### `fn is_match(&self, text: &str) -> bool`

Returns true if and only if the regex matches the string given.

It is recommended to use this method if all you need to do is test a match, since the underlying matching engine may be able to do less work.

# Example

Test if some text contains at least one word with exactly 13 Unicode word characters:

    let text = "I categorically deny having triskaidekaphobia.";
    assert!(Regex::new(r"\b\w{13}\b").unwrap().is_match(text));

#### `fn find(&self, text: &str) -> Option<(usize, usize)>`

Returns the start and end byte range of the leftmost-first match in `text`. If no match exists, then `None` is returned.

Note that this should only be used if you want to discover the position of the match. Testing the existence of a match is faster if you use `is_match`.

# Example

Find the start and end location of the first word with exactly 13 Unicode word characters:

    let text = "I categorically deny having triskaidekaphobia.";
    let pos = Regex::new(r"\b\w{13}\b").unwrap().find(text);
    assert_eq!(pos, Some((2, 15)));

#### `fn find_iter<'r, 't>(&'r self, text: &'t str) -> FindMatches<'r, 't>`

Returns an iterator for each successive non-overlapping match in `text`, returning the start and end byte indices with respect to `text`.

# Example

Find the start and end location of every word with exactly 13 Unicode word characters:

    let text = "Retroactively relinquishing remunerations is reprehensible.";
    for pos in Regex::new(r"\b\w{13}\b").unwrap().find_iter(text) {
        println!("{:?}", pos);
    }
    // Output:
    // (0, 13)
    // (14, 27)
    // (28, 41)
    // (45, 58)

#### `fn captures<'t>(&self, text: &'t str) -> Option<Captures<'t>>`

Returns the capture groups corresponding to the leftmost-first match in `text`. Capture group `0` always corresponds to the entire match. If no match is found, then `None` is returned.

You should only use `captures` if you need access to submatches. Otherwise, `find` is faster for discovering the location of the overall match.

# Examples

Say you have some text with movie names and their release years, like "'Citizen Kane' (1941)". It'd be nice if we could search for text looking like that, while also extracting the movie name and its release year separately.

    let re = Regex::new(r"'([^']+)'\s+\((\d{4})\)").unwrap();
    let text = "Not my favorite movie: 'Citizen Kane' (1941).";
    let caps = re.captures(text).unwrap();
    assert_eq!(caps.at(1), Some("Citizen Kane"));
    assert_eq!(caps.at(2), Some("1941"));
    assert_eq!(caps.at(0), Some("'Citizen Kane' (1941)"));
    // You can also access the groups by index using the Index notation.
    // Note that this will panic on an invalid index.
    assert_eq!(&caps[1], "Citizen Kane");
    assert_eq!(&caps[2], "1941");
    assert_eq!(&caps[0], "'Citizen Kane' (1941)");

Note that the full match is at capture group `0`. Each subsequent capture group is indexed by the order of its opening `(`.

We can make this example a bit clearer by using named capture groups:

    let re = Regex::new(r"'(?P<title>[^']+)'\s+\((?P<year>\d{4})\)")
                   .unwrap();
    let text = "Not my favorite movie: 'Citizen Kane' (1941).";
    let caps = re.captures(text).unwrap();
    assert_eq!(caps.name("title"), Some("Citizen Kane"));
    assert_eq!(caps.name("year"), Some("1941"));
    assert_eq!(caps.at(0), Some("'Citizen Kane' (1941)"));
    // You can also access the groups by name using the Index notation.
    // Note that this will panic on an invalid group name.
    assert_eq!(&caps["title"], "Citizen Kane");
    assert_eq!(&caps["year"], "1941");
    assert_eq!(&caps[0], "'Citizen Kane' (1941)");

Here we name the capture groups, which we can access with the `name` method or the `Index` notation with a `&str`. Note that the named capture groups are still accessible with `at` or the `Index` notation with a `usize`.

The `0`th capture group is always unnamed, so it must always be accessed with `at(0)` or `[0]`.

#### `fn captures_iter<'r, 't>(&'r self, text: &'t str) -> FindCaptures<'r, 't>`

Returns an iterator over all the non-overlapping capture groups matched in `text`. This is operationally the same as `find_iter`, except it yields information about submatches.

# Example

We can use this to find all movie titles and their release years in some text, where the movie is formatted like "'Title' (xxxx)":

    let re = Regex::new(r"'(?P<title>[^']+)'\s+\((?P<year>\d{4})\)")
                   .unwrap();
    let text = "'Citizen Kane' (1941), 'The Wizard of Oz' (1939), 'M' (1931).";
    for caps in re.captures_iter(text) {
        println!("Movie: {:?}, Released: {:?}",
                 caps.name("title"), caps.name("year"));
    }
    // Output:
    // Movie: Citizen Kane, Released: 1941
    // Movie: The Wizard of Oz, Released: 1939
    // Movie: M, Released: 1931

#### `fn split<'r, 't>(&'r self, text: &'t str) -> RegexSplits<'r, 't>`

Returns an iterator of substrings of `text` delimited by a match of the regular expression. Namely, each element of the iterator corresponds to text that isn't matched by the regular expression.

This method will not copy the text given.

# Example

To split a string delimited by arbitrary amounts of spaces or tabs:

    let re = Regex::new(r"[ \t]+").unwrap();
    let fields: Vec<&str> = re.split("a b \t  c\td    e").collect();
    assert_eq!(fields, vec!["a", "b", "c", "d", "e"]);

#### `fn splitn<'r, 't>(&'r self, text: &'t str, limit: usize) -> RegexSplitsN<'r, 't>`

Returns an iterator of at most `limit` substrings of `text` delimited by a match of the regular expression. (A `limit` of `0` will return no substrings.) Namely, each element of the iterator corresponds to text that isn't matched by the regular expression. The remainder of the string that is not split will be the last element in the iterator.

This method will not copy the text given.

# Example

Get the first two words in some text:

    let re = Regex::new(r"\W+").unwrap();
    let fields: Vec<&str> = re.splitn("Hey! How are you?", 3).collect();
    assert_eq!(fields, vec!("Hey", "How", "are you?"));

#### `fn replace<R: Replacer>(&self, text: &str, rep: R) -> String`

Replaces the leftmost-first match with the replacement provided. The replacement can be a regular string (where `$N` and `$name` are expanded to match capture groups) or a function that takes the matches' `Captures` and returns the replaced string.

If no match is found, then a copy of the string is returned unchanged.

# Examples

Note that this function is polymorphic with respect to the replacement. In typical usage, this can just be a normal string:

    let re = Regex::new("[^01]+").unwrap();
    assert_eq!(re.replace("1078910", ""), "1010");

But anything satisfying the `Replacer` trait will work. For example, a closure of type `|&Captures| -> String` provides direct access to the captures corresponding to a match. This allows one to access submatches easily:

    let re = Regex::new(r"([^,\s]+),\s+(\S+)").unwrap();
    let result = re.replace("Springsteen, Bruce", |caps: &Captures| {
        format!("{} {}", caps.at(2).unwrap_or(""), caps.at(1).unwrap_or(""))
    });
    assert_eq!(result, "Bruce Springsteen");

But this is a bit cumbersome to use all the time. Instead, a simple syntax is supported that expands `$name` into the corresponding capture group. Here's the last example, but using this expansion technique with named capture groups:

    let re = Regex::new(r"(?P<last>[^,\s]+),\s+(?P<first>\S+)").unwrap();
    let result = re.replace("Springsteen, Bruce", "$first $last");
    assert_eq!(result, "Bruce Springsteen");

Note that using `$2` instead of `$first` or `$1` instead of `$last` would produce the same result. To write a literal `$` use `$$`.

Finally, sometimes you just want to replace a literal string with no submatch expansion. This can be done by wrapping a string with `NoExpand`:

    use regex::NoExpand;

    let re = Regex::new(r"(?P<last>[^,\s]+),\s+(\S+)").unwrap();
    let result = re.replace("Springsteen, Bruce", NoExpand("$2 $last"));
    assert_eq!(result, "$2 $last");

#### `fn replace_all<R: Replacer>(&self, text: &str, rep: R) -> String`

Replaces all non-overlapping matches in `text` with the replacement provided. This is the same as calling `replacen` with `limit` set to `0`.

See the documentation for `replace` for details on how to access submatches in the replacement string.

#### `fn replacen<R: Replacer>(&self, text: &str, limit: usize, rep: R) -> String`

Replaces at most `limit` non-overlapping matches in `text` with the replacement provided. If `limit` is 0, then all non-overlapping matches are replaced.

See the documentation for `replace` for details on how to access submatches in the replacement string.

#### `fn shortest_match(&self, text: &str) -> Option<usize>`

Returns the end location of a match in the text given.

This method may have the same performance characteristics as `is_match`, except it provides an end location for a match. In particular, the location returned may be shorter than the proper end of the leftmost-first match.

# Example

Typically, `a+` would match the entire first sequence of `a` in some text, but `shortest_match` can give up as soon as it sees the first `a`.

    let text = "aaaaa";
    let pos = Regex::new(r"a+").unwrap().shortest_match(text);
    assert_eq!(pos, Some(1));

#### `fn as_str(&self) -> &str`

Returns the original string of this regex.

#### `fn capture_names(&self) -> CaptureNames`

Returns an iterator over the capture names.

#### `fn captures_len(&self) -> usize`

Returns the number of captures.

## Trait Implementations

### `impl Display for Regex`

#### `fn fmt(&self, f: &mut Formatter) -> Result`

Shows the original regular expression.

### `impl Debug for Regex`

#### `fn fmt(&self, f: &mut Formatter) -> Result`

Shows the original regular expression.

### `impl PartialEq for Regex`

Equality comparison is based on the original string. It is possible that different regular expressions have the same matching behavior, but are still compared unequal. For example, `\d+` and `\d\d*` match the same set of strings, but are not considered equal.

#### `fn eq(&self, other: &Regex) -> bool`

#### `fn ne(&self, other: &Rhs) -> bool` 1.0.0

### `impl Eq for Regex`

### `impl FromStr for Regex`

#### `type Err = Error`

#### `fn from_str(s: &str) -> Result<Regex, Error>`

Attempts to parse a string into a regular expression

### Derived Implementations

### `impl Clone for Regex`

#### `fn clone(&self) -> Regex`

#### `fn clone_from(&mut self, source: &Self)`1.0.0

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