Regex

Introduction #

Regular expressions for Elixir built on top of Erlang's re module.

As the re module, Regex is based on PCRE (Perl Compatible Regular Expressions). More information can be found in the re documentation.

Regular expressions in Elixir can be created using Regex.compile!/2 or using the special form with ~r:

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

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

A Regex is represented internally as the Regex struct. Therefore, %Regex{} can be used whenever there is a need to match on them.

Modifiers

The modifiers available when creating a Regex are:

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

  • caseless (i) - add 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 (r) - inverts the "greediness" of the regexp

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 allows 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 - do not return matching subpatterns at all

  • :all_names - captures all names in the Regex

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

Source

Types #

t

Functions #

compile(source, options \\ "")

(function)

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 sigil, or a list of options, as expected by the Erlang re docs.

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 \\ "")

(function)

Compiles the regular expression according to the given options. Fails with Regex.CompileError if the regex cannot be compiled.

escape(string)

(function)

Specs

Escapes a string to be literally matched in a regex.

Examples

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

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

match?(regex, string)

(function)

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 \\ [])

(function)

Returns the given captures as a map or nil if no captures are found. The option :return can be set to :index to get indexes back.

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)

(function)

Returns a list of names in the regex.

Examples

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

opts(regex)

(function)

Returns the regex options as a string.

Examples

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

re_pattern(regex)

(function)

Returns the underlying re_pattern in the regular expression.

regex?(regex)

(function)

Returns true if the given argument is a regex.

Examples

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

iex> Regex.regex?(0)
false

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

(function)

Receives a regex, a binary and a replacement, returns a new binary where the all matches are replaced by 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, where N is the capture. In case \0 is used, the whole match is inserted.

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/a(b|d)c/, "abcadc", fn _, x -> "[#{x}]" end)
"[b][d]"

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

(function)

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 - set to :index to return indexes. 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 \\ [])

(function)

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 - set to :index to return indexes. 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")
[]

source(regex)

(function)

Returns the regex source as a binary.

Examples

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

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

(function)

Splits the given target into the number of parts specified.

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, remove blank strings from the result.

  • :on - specifies which captures and order to split the string on. Check the moduledoc for Regex to see the possible capture values. Defaults to :first which means captures inside the Regex does not affect the split result.

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"]