Regex

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 :re module documentation.

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.

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.

Types

t()

Specs

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

Functions

compile(source, options \\ "")

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}}

compile!(source, options \\ "")

Specs

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

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

escape(string)

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"

match?(regex, string)

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

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

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

names(regex)

Specs

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

Returns a list of names in the regex.

Examples

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

opts(regex)

Specs

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

Returns the regex options as a string.

Examples

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

re_pattern(regex)

Specs

re_pattern(t()) :: term()

Returns the underlying re_pattern in the regular expression.

recompile(regex)

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.

recompile!(regex)

Specs

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

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

regex?(term)

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

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

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"

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

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}]

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

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}]]

source(regex)

Specs

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

Returns the regex source as a binary.

Examples

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

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

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"]

version()

Specs

version() :: term()

Returns the version of the underlying Regex engine.