Struct Regex

pub struct Regex { /* private fields */ }

A compiled regular expression.

Implementations

impl Regex

pub fn new(re: &str) -> Result<Regex>

Parse and compile a regex with default options, see RegexBuilder.

Returns an Error if the pattern could not be parsed.

pub fn as_str(&self) -> &str

Returns the original string of this regex.

pub fn is_match(&self, text: &str) -> Result<bool>

Check if the regex matches the input text.

Example

Test if some text contains the same word twice:

let re = Regex::new(r"(\w+) \1").unwrap();
assert!(re.is_match("mirror mirror on the wall").unwrap());

pub fn find_iter<'r, 't>(&'r self, text: &'t str) -> Matches<'r, 't>

Returns an iterator for each successive non-overlapping match in text.

If you have capturing groups in your regex that you want to extract, use the Regex::captures_iter() method.

Example

Find all words followed by an exclamation point:

let re = Regex::new(r"\w+(?=!)").unwrap();
let mut matches = re.find_iter("so fancy! even with! iterators!");
assert_eq!(matches.next().unwrap().unwrap().as_str(), "fancy");
assert_eq!(matches.next().unwrap().unwrap().as_str(), "with");
assert_eq!(matches.next().unwrap().unwrap().as_str(), "iterators");
assert!(matches.next().is_none());

pub fn find<'t>(&self, text: &'t str) -> Result<Option<Match<'t>>>

Find the first match in the input text.

If you have capturing groups in your regex that you want to extract, use the Regex::captures() method.

Example

Find a word that is followed by an exclamation point:

let re = Regex::new(r"\w+(?=!)").unwrap();
assert_eq!(re.find("so fancy!").unwrap().unwrap().as_str(), "fancy");

pub fn find_from_pos<'t>( &self, text: &'t str, pos: usize, ) -> Result<Option<Match<'t>>>

Returns the first match in text, starting from the specified byte position pos.

Examples

Finding match starting at a position:

let re = Regex::new(r"(?m:^)(\d+)").unwrap();
let text = "1 test 123\n2 foo";
let mat = re.find_from_pos(text, 7).unwrap().unwrap();

assert_eq!(mat.start(), 11);
assert_eq!(mat.end(), 12);

Note that in some cases this is not the same as using the find method and passing a slice of the string, see Regex::captures_from_pos() for details.

pub fn captures_iter<'r, 't>(&'r self, text: &'t str) -> CaptureMatches<'r, 't>

Returns an iterator over all the non-overlapping capture groups matched in text.

Examples

Finding all matches and capturing parts of each:

let re = Regex::new(r"(\d{4})-(\d{2})").unwrap();
let text = "It was between 2018-04 and 2020-01";
let mut all_captures = re.captures_iter(text);

let first = all_captures.next().unwrap().unwrap();
assert_eq!(first.get(1).unwrap().as_str(), "2018");
assert_eq!(first.get(2).unwrap().as_str(), "04");
assert_eq!(first.get(0).unwrap().as_str(), "2018-04");

let second = all_captures.next().unwrap().unwrap();
assert_eq!(second.get(1).unwrap().as_str(), "2020");
assert_eq!(second.get(2).unwrap().as_str(), "01");
assert_eq!(second.get(0).unwrap().as_str(), "2020-01");

assert!(all_captures.next().is_none());

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

Returns the capture groups for the first match in text.

If no match is found, then Ok(None) is returned.

Examples

Finding matches and capturing parts of the match:

let re = Regex::new(r"(\d{4})-(\d{2})-(\d{2})").unwrap();
let text = "The date was 2018-04-07";
let captures = re.captures(text).unwrap().unwrap();

assert_eq!(captures.get(1).unwrap().as_str(), "2018");
assert_eq!(captures.get(2).unwrap().as_str(), "04");
assert_eq!(captures.get(3).unwrap().as_str(), "07");
assert_eq!(captures.get(0).unwrap().as_str(), "2018-04-07");

pub fn captures_from_pos<'t>( &self, text: &'t str, pos: usize, ) -> Result<Option<Captures<'t>>>

Returns the capture groups for the first match in text, starting from the specified byte position pos.

Examples

Finding captures starting at a position:

let re = Regex::new(r"(?m:^)(\d+)").unwrap();
let text = "1 test 123\n2 foo";
let captures = re.captures_from_pos(text, 7).unwrap().unwrap();

let group = captures.get(1).unwrap();
assert_eq!(group.as_str(), "2");
assert_eq!(group.start(), 11);
assert_eq!(group.end(), 12);

Note that in some cases this is not the same as using the captures method and passing a slice of the string, see the capture that we get when we do this:

let re = Regex::new(r"(?m:^)(\d+)").unwrap();
let text = "1 test 123\n2 foo";
let captures = re.captures(&text[7..]).unwrap().unwrap();
assert_eq!(captures.get(1).unwrap().as_str(), "123");

This matched the number “123” because it’s at the beginning of the text of the string slice.

pub fn captures_len(&self) -> usize

Returns the number of captures, including the implicit capture of the entire expression.

pub fn capture_names(&self) -> CaptureNames<'_>

Returns an iterator over the capture names.

pub fn replace<'t, R: Replacer>(&self, text: &'t str, rep: R) -> Cow<'t, str>

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.

Replacement string syntax

All instances of $name in the replacement text is replaced with the corresponding capture group name.

name may be an integer corresponding to the index of the capture group (counted by order of opening parenthesis where 0 is the entire match) or it can be a name (consisting of letters, digits or underscores) corresponding to a named capture group.

If name isn’t a valid capture group (whether the name doesn’t exist or isn’t a valid index), then it is replaced with the empty string.

The longest possible name is used. e.g., $1a looks up the capture group named 1a and not the capture group at index 1. To exert more precise control over the name, use braces, e.g., ${1}a.

To write a literal $ use $$.

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 capturing group matches easily:

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

Sometimes the replacement string requires use of curly braces to delineate a capture group replacement and surrounding literal text. For example, if we wanted to join two words together with an underscore:

let re = Regex::new(r"(?P<first>\w+)\s+(?P<second>\w+)").unwrap();
let result = re.replace("deep fried", "${first}_$second");
assert_eq!(result, "deep_fried");

Without the curly braces, the capture group name first_ would be used, and since it doesn’t exist, it would be replaced with the empty string.

Finally, sometimes you just want to replace a literal string with no regard for capturing group expansion. This can be done by wrapping a byte string with NoExpand:

use fancy_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");

pub fn replace_all<'t, R: Replacer>( &self, text: &'t str, rep: R, ) -> Cow<'t, str>

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 capturing group matches in the replacement string.

pub fn replacen<'t, R: Replacer>( &self, text: &'t str, limit: usize, rep: R, ) -> Cow<'t, str>

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 capturing group matches in the replacement string.

Trait Implementations

impl Clone for Regex

fn clone(&self) -> Regex

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Regex

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Shows the original regular expression.

impl Display for Regex

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Shows the original regular expression

impl FromStr for Regex

fn from_str(s: &str) -> Result<Regex>

Attempts to parse a string into a regular expression

type Err = Error

The associated error which can be returned from parsing.