# Elixir v1.10.3 Regex View Source

Provides regular expressions for Elixir.

Regex is based on PCRE (Perl Compatible Regular Expressions) and built on top of Erlang's `:re` module. More information can be found in the module documentation`:re`.

Regular expressions in Elixir can be created using the sigils `~r` (see `Kernel.sigil_r/2`) or `~R` (see `Kernel.sigil_R/2`):

    # A simple regular expression that matches foo anywhere in the string
    ~r/foo/

    # A regular expression with case insensitive and Unicode options
    ~r/foo/iu

Regular expressions created via sigils are pre-compiled and stored in the `.beam` file. Notice this may be a problem if you are precompiling Elixir, see the "Precompilation" section for more information.

A Regex is represented internally as the `Regex` struct. Therefore, `%Regex{}` can be used whenever there is a need to match on them. Keep in mind it is not guaranteed two regular expressions from the same source are equal, for example:

    ~r/(?<foo>.)(?<bar>.)/ == ~r/(?<foo>.)(?<bar>.)/

may return `true` or `false` depending on your machine, endianness, available optimizations and others. You can, however, retrieve the source of a compiled regular expression by accessing the `source` field, and then compare those directly:

    ~r/(?<foo>.)(?<bar>.)/.source == ~r/(?<foo>.)(?<bar>.)/.source

## Modifiers

The modifiers available when creating a Regex are:

- `unicode` (u) - enables Unicode specific patterns like `\p` and change modifiers like `\w`, `\W`, `\s` and friends to also match on Unicode. It expects valid Unicode strings to be given on match

- `caseless` (i) - adds case insensitivity

- `dotall` (s) - causes dot to match newlines and also set newline to anycrlf; the new line setting can be overridden by setting `(*CR)` or `(*LF)` or `(*CRLF)` or `(*ANY)` according to `:re` documentation

- `multiline` (m) - causes `^` and `$` to mark the beginning and end of each line; use `\A` and `\z` to match the end or beginning of the string

- `extended` (x) - whitespace characters are ignored except when escaped and allow `#` to delimit comments

- `firstline` (f) - forces the unanchored pattern to match before or at the first newline, though the matched text may continue over the newline

- `ungreedy` (U) - inverts the "greediness" of the regexp (the previous `r` option is deprecated in favor of `U`)

The options not available are:

- `anchored` - not available, use `^` or `\A` instead
- `dollar_endonly` - not available, use `\z` instead
- `no_auto_capture` - not available, use `?:` instead
- `newline` - not available, use `(*CR)` or `(*LF)` or `(*CRLF)` or `(*ANYCRLF)` or `(*ANY)` at the beginning of the regexp according to the `:re` documentation

## Captures

Many functions in this module handle what to capture in a regex match via the `:capture` option. The supported values are:

- `:all` - all captured subpatterns including the complete matching string (this is the default)

- `:first` - only the first captured subpattern, which is always the complete matching part of the string; all explicitly captured subpatterns are discarded

- `:all_but_first` - all but the first matching subpattern, i.e. all explicitly captured subpatterns, but not the complete matching part of the string

- `:none` - does not return matching subpatterns at all

- `:all_names` - captures all named subpattern matches in the Regex as a list ordered alphabetically by the names of the subpatterns

- `list(binary)` - a list of named captures to capture

## Character classes

Regex supports several built in named character classes. These are used by enclosing the class name in `[: :]` inside a group. For example:

    iex> String.match?("123", ~r/^[[:alnum:]]+$/)
    true
    iex> String.match?("123 456", ~r/^[[:alnum:][:blank:]]+$/)
    true

The supported class names are:

- alnum - Letters and digits
- alpha - Letters
- ascii - Character codes 0-127
- blank - Space or tab only
- cntrl - Control characters
- digit - Decimal digits (same as \d)
- graph - Printing characters, excluding space
- lower - Lowercase letters
- print - Printing characters, including space
- punct - Printing characters, excluding letters, digits, and space
- space - Whitespace (the same as \s from PCRE 8.34)
- upper - Uppercase letters
- word - "Word" characters (same as \w)
- xdigit - Hexadecimal digits

Note the behaviour of those classes may change according to the Unicode and other modifiers:

    iex> String.match?("josé", ~r/^[[:lower:]]+$/)
    false
    iex> String.match?("josé", ~r/^[[:lower:]]+$/u)
    true

## Precompilation

Regular expressions built with sigil are precompiled and stored in `.beam` files. Precompiled regexes will be checked in runtime and may work slower between operating systems and OTP releases. This is rarely a problem, as most Elixir code shared during development is compiled on the target (such as dependencies, archives, and escripts) and, when running in production, the code must either be compiled on the target (via `mix compile` or similar) or released on the host (via `mix releases` or similar) with a matching OTP, operating system and architecture as the target.

If you know you are running on a different system than the current one and you are doing multiple matches with the regex, you can manually invoke `Regex.recompile/1` or `Regex.recompile!/1` to perform a runtime version check and recompile the regex if necessary.

# Link to this section Summary

## Types

t()

## Functions

compile(source, options \\ "")

Compiles the regular expression.

compile!(source, options \\ "")

Compiles the regular expression and raises `Regex.CompileError` in case of errors.

escape(string)

Escapes a string to be literally matched in a regex.

match?(regex, string)

Returns a boolean indicating whether there was a match or not.

named_captures(regex, string, options \\ [])

Returns the given captures as a map or `nil` if no captures are found.

names(regex)

Returns a list of names in the regex.

opts(regex)

Returns the regex options as a string.

re_pattern(regex)

Returns the underlying `re_pattern` in the regular expression.

recompile(regex)

Recompiles the existing regular expression if necessary.

recompile!(regex)

Recompiles the existing regular expression and raises `Regex.CompileError` in case of errors.

regex?(term)

Returns `true` if the given `term` is a regex. Otherwise returns `false`.

replace(regex, string, replacement, options \\ [])

Receives a regex, a binary and a replacement, returns a new binary where all matches are replaced by the replacement.

run(regex, string, options \\ [])

Runs the regular expression against the given string until the first match. It returns a list with all captures or `nil` if no match occurred.

scan(regex, string, options \\ [])

Same as `run/3`, but scans the target several times collecting all matches of the regular expression.

source(regex)

Returns the regex source as a binary.

split(regex, string, options \\ [])

Splits the given target based on the given pattern and in the given number of parts.

version()

Returns the version of the underlying Regex engine.

# Link to this section Types

Link to this type

# t()

View Source

## Specs

    t() :: %Regex{
      opts: binary(),
      re_pattern: term(),
      re_version: term(),
      source: binary()
    }

# Link to this section Functions

Link to this function

# compile(source, options \\ "")

View Source

## Specs

    compile(binary(), binary() | [term()]) :: {:ok, t()} | {:error, any()}

Compiles the regular expression.

The given options can either be a binary with the characters representing the same regex options given to the `~r` (see `Kernel.sigil_r/2`) sigil, or a list of options, as expected by the Erlang's `:re` module.

It returns `{:ok, regex}` in case of success, `{:error, reason}` otherwise.

## Examples

    iex> Regex.compile("foo")
    {:ok, ~r/foo/}

    iex> Regex.compile("*foo")
    {:error, {'nothing to repeat', 0}}

Link to this function

# compile!(source, options \\ "")

View Source

## Specs

    compile!(binary(), binary() | [term()]) :: t()

Compiles the regular expression and raises `Regex.CompileError` in case of errors.

Link to this function

# escape(string)

View Source

## Specs

    escape(String.t()) :: String.t()

Escapes a string to be literally matched in a regex.

## Examples

    iex> Regex.escape(".")
    "\\."

    iex> Regex.escape("\\what if")
    "\\\\what\\ if"

Link to this function

# match?(regex, string)

View Source

## Specs

    match?(t(), String.t()) :: boolean()

Returns a boolean indicating whether there was a match or not.

## Examples

    iex> Regex.match?(~r/foo/, "foo")
    true

    iex> Regex.match?(~r/foo/, "bar")
    false

Link to this function

# named_captures(regex, string, options \\ [])

View Source

## Specs

    named_captures(t(), String.t(), [term()]) :: map() | nil

Returns the given captures as a map or `nil` if no captures are found.

## Options

- `:return` - when set to `:index`, returns byte index and match length. Defaults to `:binary`.

## Examples

    iex> Regex.named_captures(~r/c(?<foo>d)/, "abcd")
    %{"foo" => "d"}

    iex> Regex.named_captures(~r/a(?<foo>b)c(?<bar>d)/, "abcd")
    %{"bar" => "d", "foo" => "b"}

    iex> Regex.named_captures(~r/a(?<foo>b)c(?<bar>d)/, "efgh")
    nil

Link to this function

# names(regex)

View Source

## Specs

    names(t()) :: [String.t()]

Returns a list of names in the regex.

## Examples

    iex> Regex.names(~r/(?<foo>bar)/)
    ["foo"]

Link to this function

# opts(regex)

View Source

## Specs

    opts(t()) :: String.t()

Returns the regex options as a string.

## Examples

    iex> Regex.opts(~r(foo)m)
    "m"

Link to this function

# re_pattern(regex)

View Source

## Specs

    re_pattern(t()) :: term()

Returns the underlying `re_pattern` in the regular expression.

Link to this function

# recompile(regex)

View Source (since 1.4.0)

## Specs

    recompile(t()) :: t()

Recompiles the existing regular expression if necessary.

This checks the version stored in the regular expression and recompiles the regex in case of version mismatch.

Link to this function

# recompile!(regex)

View Source (since 1.4.0)

## Specs

    recompile!(t()) :: t()

Recompiles the existing regular expression and raises `Regex.CompileError` in case of errors.

Link to this function

# regex?(term)

View Source

## Specs

    regex?(any()) :: boolean()

Returns `true` if the given `term` is a regex. Otherwise returns `false`.

## Examples

    iex> Regex.regex?(~r/foo/)
    true

    iex> Regex.regex?(0)
    false

Link to this function

# replace(regex, string, replacement, options \\ [])

View Source

## Specs

    replace(t(), String.t(), String.t() | (... -> String.t()), [term()]) ::
      String.t()

Receives a regex, a binary and a replacement, returns a new binary where all matches are replaced by the replacement.

The replacement can be either a string or a function. The string is used as a replacement for every match and it allows specific captures to be accessed via `\N` or `\g{N}`, where `N` is the capture. In case `\0` is used, the whole match is inserted. Note that in regexes the backslash needs to be escaped, hence in practice you'll need to use `\\N` and `\\g{N}`.

When the replacement is a function, the function may have arity N where each argument maps to a capture, with the first argument being the whole match. If the function expects more arguments than captures found, the remaining arguments will receive `""`.

## Options

- `:global` - when `false`, replaces only the first occurrence (defaults to `true`)

## Examples

    iex> Regex.replace(~r/d/, "abc", "d")
    "abc"

    iex> Regex.replace(~r/b/, "abc", "d")
    "adc"

    iex> Regex.replace(~r/b/, "abc", "[\\0]")
    "a[b]c"

    iex> Regex.replace(~r/a(b|d)c/, "abcadc", "[\\1]")
    "[b][d]"

    iex> Regex.replace(~r/\.(\d)$/, "500.5", ".\\g{1}0")
    "500.50"

    iex> Regex.replace(~r/a(b|d)c/, "abcadc", fn _, x -> "[#{x}]" end)
    "[b][d]"

    iex> Regex.replace(~r/a/, "abcadc", "A", global: false)
    "Abcadc"

Link to this function

# run(regex, string, options \\ [])

View Source

## Specs

    run(t(), binary(), [term()]) :: nil | [binary()] | [{integer(), integer()}]

Runs the regular expression against the given string until the first match. It returns a list with all captures or `nil` if no match occurred.

## Options

- `:return` - when set to `:index`, returns byte index and match length. Defaults to `:binary`.
- `:capture` - what to capture in the result. Check the moduledoc for `Regex` to see the possible capture values.

## Examples

    iex> Regex.run(~r/c(d)/, "abcd")
    ["cd", "d"]

    iex> Regex.run(~r/e/, "abcd")
    nil

    iex> Regex.run(~r/c(d)/, "abcd", return: :index)
    [{2, 2}, {3, 1}]

Link to this function

# scan(regex, string, options \\ [])

View Source

## Specs

    scan(t(), String.t(), [term()]) :: [[String.t()]]

Same as `run/3`, but scans the target several times collecting all matches of the regular expression.

A list of lists is returned, where each entry in the primary list represents a match and each entry in the secondary list represents the captured contents.

## Options

- `:return` - when set to `:index`, returns byte index and match length. Defaults to `:binary`.
- `:capture` - what to capture in the result. Check the moduledoc for `Regex` to see the possible capture values.

## Examples

    iex> Regex.scan(~r/c(d|e)/, "abcd abce")
    [["cd", "d"], ["ce", "e"]]

    iex> Regex.scan(~r/c(?:d|e)/, "abcd abce")
    [["cd"], ["ce"]]

    iex> Regex.scan(~r/e/, "abcd")
    []

    iex> Regex.scan(~r/\p{Sc}/u, "$, £, and €")
    [["$"], ["£"], ["€"]]

    iex> Regex.scan(~r/=+/, "=ü†ƒ8===", return: :index)
    [[{0, 1}], [{9, 3}]]

Link to this function

# source(regex)

View Source

## Specs

    source(t()) :: String.t()

Returns the regex source as a binary.

## Examples

    iex> Regex.source(~r(foo))
    "foo"

Link to this function

# split(regex, string, options \\ [])

View Source

## Specs

    split(t(), String.t(), [term()]) :: [String.t()]

Splits the given target based on the given pattern and in the given number of parts.

## Options

- `:parts` - when specified, splits the string into the given number of parts. If not specified, `:parts` defaults to `:infinity`, which will split the string into the maximum number of parts possible based on the given pattern.

- `:trim` - when `true`, removes empty strings (`""`) from the result. Defaults to `false`.

- `:on` - specifies which captures to split the string on, and in what order. Defaults to `:first` which means captures inside the regex do not affect the splitting process.

- `:include_captures` - when `true`, includes in the result the matches of the regular expression. The matches are not counted towards the maximum number of parts if combined with the `:parts` option. Defaults to `false`.

## Examples

    iex> Regex.split(~r{-}, "a-b-c")
    ["a", "b", "c"]

    iex> Regex.split(~r{-}, "a-b-c", parts: 2)
    ["a", "b-c"]

    iex> Regex.split(~r{-}, "abc")
    ["abc"]

    iex> Regex.split(~r{}, "abc")
    ["", "a", "b", "c", ""]

    iex> Regex.split(~r{a(?<second>b)c}, "abc")
    ["", ""]

    iex> Regex.split(~r{a(?<second>b)c}, "abc", on: [:second])
    ["a", "c"]

    iex> Regex.split(~r{(x)}, "Elixir", include_captures: true)
    ["Eli", "x", "ir"]

    iex> Regex.split(~r{a(?<second>b)c}, "abc", on: [:second], include_captures: true)
    ["a", "b", "c"]

Link to this function

# version()

View Source (since 1.4.0)

## Specs

    version() :: term()

Returns the version of the underlying Regex engine.