String

A String in Elixir is a UTF-8 encoded binary.

Codepoints and grapheme cluster

The functions in this module act according to the Unicode Standard, version 10.0.0.

As per the standard, a codepoint is a single Unicode Character, which may be represented by one or more bytes.

For example, the codepoint “é” is two bytes:

iex> byte_size("é")
2

However, this module returns the proper length:

iex> String.length("é")
1

Furthermore, this module also presents the concept of grapheme cluster (from now on referenced as graphemes). Graphemes can consist of multiple codepoints that may be perceived as a single character by readers. For example, “é” can be represented either as a single “e with acute” codepoint or as the letter “e” followed by a “combining acute accent” (two codepoints):

iex> string = "\u0065\u0301"
iex> byte_size(string)
3
iex> String.length(string)
1
iex> String.codepoints(string)
["e", "́"]
iex> String.graphemes(string)
["é"]

Although the example above is made of two characters, it is perceived by users as one.

Graphemes can also be two characters that are interpreted as one by some languages. For example, some languages may consider “ch” as a single character. However, since this information depends on the locale, it is not taken into account by this module.

In general, the functions in this module rely on the Unicode Standard, but do not contain any of the locale specific behaviour.

More information about graphemes can be found in the Unicode Standard Annex #29. The current Elixir version implements Extended Grapheme Cluster algorithm.

For converting a binary to a different encoding and for Unicode normalization mechanisms, see Erlang’s :unicode module.

String and binary operations

To act according to the Unicode Standard, many functions in this module run in linear time, as they need to traverse the whole string considering the proper Unicode codepoints.

For example, String.length/1 will take longer as the input grows. On the other hand, Kernel.byte_size/1 always runs in constant time (i.e. regardless of the input size).

This means often there are performance costs in using the functions in this module, compared to the more low-level operations that work directly with binaries:

Kernel.binary_part/3 - retrieves part of the binary
Kernel.bit_size/1 and Kernel.byte_size/1 - size related functions
Kernel.is_bitstring/1 and Kernel.is_binary/1 - type checking function
Plus a number of functions for working with binaries (bytes) in the :binary module

There are many situations where using the String module can be avoided in favor of binary functions or pattern matching. For example, imagine you have a string prefix and you want to remove this prefix from another string named full.

One may be tempted to write:

iex> take_prefix = fn full, prefix ->
...>   base = String.length(prefix)
...>   String.slice(full, base, String.length(full) - base)
...> end
iex> take_prefix.("Mr. John", "Mr. ")
"John"

Although the function above works, it performs poorly. To calculate the length of the string, we need to traverse it fully, so we traverse both prefix and full strings, then slice the full one, traversing it again.

A first attempt at improving it could be with ranges:

iex> take_prefix = fn full, prefix ->
...>   base = String.length(prefix)
...>   String.slice(full, base..-1)
...> end
iex> take_prefix.("Mr. John", "Mr. ")
"John"

While this is much better (we don’t traverse full twice), it could still be improved. In this case, since we want to extract a substring from a string, we can use Kernel.byte_size/1 and Kernel.binary_part/3 as there is no chance we will slice in the middle of a codepoint made of more than one byte:

iex> take_prefix = fn full, prefix ->
...>   base = byte_size(prefix)
...>   binary_part(full, base, byte_size(full) - base)
...> end
iex> take_prefix.("Mr. John", "Mr. ")
"John"

Or simply use pattern matching:

iex> take_prefix = fn full, prefix ->
...>   base = byte_size(prefix)
...>   <<_::binary-size(base), rest::binary>> = full
...>   rest
...> end
iex> take_prefix.("Mr. John", "Mr. ")
"John"

On the other hand, if you want to dynamically slice a string based on an integer value, then using String.slice/3 is the best option as it guarantees we won’t incorrectly split a valid codepoint into multiple bytes.

Integer codepoints

Although codepoints could be represented as integers, this module represents all codepoints as strings. For example:

iex> String.codepoints("olá")
["o", "l", "á"]

There are a couple of ways to retrieve a character integer codepoint. One may use the ? construct:

iex> ?o
111

iex> ?á
225

Or also via pattern matching:

iex> <<aacute::utf8>> = "á"
iex> aacute
225

As we have seen above, codepoints can be inserted into a string by their hexadecimal code:

"ol\u0061\u0301" #=>
"olá"

Self-synchronization

The UTF-8 encoding is self-synchronizing. This means that if malformed data (i.e., data that is not possible according to the definition of the encoding) is encountered, only one codepoint needs to be rejected.

This module relies on this behaviour to ignore such invalid characters. For example, length/1 will return a correct result even if an invalid codepoint is fed into it.

In other words, this module expects invalid data to be detected elsewhere, usually when retrieving data from the external source. For example, a driver that reads strings from a database will be responsible to check the validity of the encoding. String.chunk/2 can be used for breaking a string into valid and invalid parts.

Patterns

Many functions in this module work with patterns. For example, String.split/2 can split a string into multiple patterns given a pattern. This pattern can be a string, a list of strings or a compiled pattern:

iex> String.split("foo bar", " ")
["foo", "bar"]

iex> String.split("foo bar!", [" ", "!"])
["foo", "bar", ""]

iex> pattern = :binary.compile_pattern([" ", "!"])
iex> String.split("foo bar!", pattern)
["foo", "bar", ""]

The compiled pattern is useful when the same match will be done over and over again. Note though the compiled pattern cannot be stored in a module attribute as the pattern is generated at runtime and does not survive compile term.

Summary

Functions

at(string, position): Returns the grapheme at the position of the given UTF-8 string. If position is greater than string length, then it returns nil
capitalize(string, mode \\ :default): Converts the first character in the given string to uppercase and the remainder to lowercase according to mode
chunk(string, trait): Splits the string into chunks of characters that share a common trait
codepoints(string): Returns all codepoints in the string
contains?(string, contents): Checks if string contains any of the given contents
downcase(string, mode \\ :default): Converts all characters in the given string to lowercase according to mode
duplicate(subject, n): Returns a string subject duplicated n times
ends_with?(string, suffixes): Returns true if string ends with any of the suffixes given
equivalent?(string1, string2): Returns true if string1 is canonically equivalent to ‘string2’
first(string): Returns the first grapheme from a UTF-8 string, nil if the string is empty
graphemes(string): Returns Unicode graphemes in the string as per Extended Grapheme Cluster algorithm
jaro_distance(string1, string2): Returns a float value between 0 (equates to no similarity) and 1 (is an exact match) representing Jaro distance between string1 and string2
last(string): Returns the last grapheme from a UTF-8 string, nil if the string is empty
length(string): Returns the number of Unicode graphemes in a UTF-8 string
match?(string, regex): Checks if string matches the given regular expression
myers_difference(string1, string2): Returns a keyword list that represents an edit script
next_codepoint(string): Returns the next codepoint in a string
next_grapheme(binary): Returns the next grapheme in a string
next_grapheme_size(string): Returns the size of the next grapheme
normalize(string, form): Converts all characters in string to Unicode normalization form identified by form
pad_leading(string, count, padding \\ [" "]): Returns a new string padded with a leading filler which is made of elements from the padding
pad_trailing(string, count, padding \\ [" "]): Returns a new string padded with a trailing filler which is made of elements from the padding
printable?(string, counter \\ :infinity): Checks if a string contains only printable characters
replace(subject, pattern, replacement, options \\ []): Returns a new string created by replacing occurrences of pattern in subject with replacement
replace_leading(string, match, replacement): Replaces all leading occurrences of match by replacement of match in string
replace_prefix(string, match, replacement): Replaces prefix in string by replacement if it matches match
replace_suffix(string, match, replacement): Replaces suffix in string by replacement if it matches match
replace_trailing(string, match, replacement): Replaces all trailing occurrences of match by replacement in string
reverse(string): Reverses the graphemes in given string
slice(string, range): Returns a substring from the offset given by the start of the range to the offset given by the end of the range
slice(string, start, len): Returns a substring starting at the offset start, and of length len
split(binary): Divides a string into substrings at each Unicode whitespace occurrence with leading and trailing whitespace ignored. Groups of whitespace are treated as a single occurrence. Divisions do not occur on non-breaking whitespace
split(string, pattern, options \\ []): Divides a string into substrings based on a pattern
split_at(string, position): Splits a string into two at the specified offset. When the offset given is negative, location is counted from the end of the string
splitter(string, pattern, options \\ []): Returns an enumerable that splits a string on demand
starts_with?(string, prefix): Returns true if string starts with any of the prefixes given
to_atom(string): Converts a string to an atom
to_charlist(string): Converts a string into a charlist
to_existing_atom(string): Converts a string to an existing atom
to_float(string): Returns a float whose text representation is string
to_integer(string): Returns an integer whose text representation is string
to_integer(string, base): Returns an integer whose text representation is string in base base
trim(string): Returns a string where all leading and trailing Unicode whitespaces have been removed
trim(string, to_trim): Returns a string where all leading and trailing to_trims have been removed
trim_leading(string): Returns a string where all leading Unicode whitespaces have been removed
trim_leading(string, to_trim): Returns a string where all leading to_trims have been removed
trim_trailing(string): Returns a string where all trailing Unicode whitespaces has been removed
trim_trailing(string, to_trim): Returns a string where all trailing to_trims have been removed
upcase(string, mode \\ :default): Converts all characters in the given string to uppercase according to mode
valid?(string): Checks whether string contains only valid characters

Types

codepoint()

codepoint() :: t()

grapheme()

grapheme() :: t()

pattern()

pattern() :: t() | [t()] | :binary.cp()

t()

t() :: binary()

Functions

at(string, position)

at(t(), integer()) :: grapheme() | nil

Returns the grapheme at the position of the given UTF-8 string. If position is greater than string length, then it returns nil.

Examples

iex> String.at("elixir", 0)
"e"

iex> String.at("elixir", 1)
"l"

iex> String.at("elixir", 10)
nil

iex> String.at("elixir", -1)
"r"

iex> String.at("elixir", -10)
nil

capitalize(string, mode \\ :default)

capitalize(t(), :default | :ascii | :greek) :: t()

Converts the first character in the given string to uppercase and the remainder to lowercase according to mode.

mode may be :default, :ascii or :greek. The :default mode considers all non-conditional transformations outlined in the Unicode standard. :ascii lowercases only the letters A to Z. :greek includes the context sensitive mappings found in Greek.

Examples

iex> String.capitalize("abcd")
"Abcd"

iex> String.capitalize("ﬁn")
"Fin"

iex> String.capitalize("olá")
"Olá"

chunk(string, trait)

chunk(t(), :valid | :printable) :: [t()]

Splits the string into chunks of characters that share a common trait.

The trait can be one of two options:

:valid - the string is split into chunks of valid and invalid character sequences
:printable - the string is split into chunks of printable and non-printable character sequences

Returns a list of binaries each of which contains only one kind of characters.

If the given string is empty, an empty list is returned.

Examples

iex> String.chunk(<<?a, ?b, ?c, 0>>, :valid)
["abc\0"]

iex> String.chunk(<<?a, ?b, ?c, 0, 0xFFFF::utf16>>, :valid)
["abc\0", <<0xFFFF::utf16>>]

iex> String.chunk(<<?a, ?b, ?c, 0, 0x0FFFF::utf8>>, :printable)
["abc", <<0, 0x0FFFF::utf8>>]

codepoints(string)

codepoints(t()) :: [codepoint()]

Returns all codepoints in the string.

For details about codepoints and graphemes, see the String module documentation.

Examples

iex> String.codepoints("olá")
["o", "l", "á"]

iex> String.codepoints("оптими зации")
["о", "п", "т", "и", "м", "и", " ", "з", "а", "ц", "и", "и"]

iex> String.codepoints("ἅἪῼ")
["ἅ", "Ἢ", "ῼ"]

iex> String.codepoints("é")
["é"]

iex> String.codepoints("é")
["e", "́"]

contains?(string, contents)

contains?(t(), pattern()) :: boolean()

Checks if string contains any of the given contents.

contents can be either a single string or a list of strings.

Examples

iex> String.contains? "elixir of life", "of"
true
iex> String.contains? "elixir of life", ["life", "death"]
true
iex> String.contains? "elixir of life", ["death", "mercury"]
false

An empty string will always match:

iex> String.contains? "elixir of life", ""
true
iex> String.contains? "elixir of life", ["", "other"]
true

The argument can also be a precompiled pattern:

iex> pattern = :binary.compile_pattern(["life", "death"])
iex> String.contains? "elixir of life", pattern
true

Note this function can match within or across grapheme boundaries. For example, take the grapheme “é” which is made of the characters “e” and the acute accent. The following returns true:

iex> String.contains?(String.normalize("é", :nfd), "e")
true

However, if “é” is represented by the single character “e with acute” accent, then it will return false:

iex> String.contains?(String.normalize("é", :nfc), "e")
false

downcase(string, mode \\ :default)

downcase(t(), :default | :ascii | :greek) :: t()

Converts all characters in the given string to lowercase according to mode.

Examples

iex> String.downcase("ABCD")
"abcd"

iex> String.downcase("AB 123 XPTO")
"ab 123 xpto"

iex> String.downcase("OLÁ")
"olá"

The :ascii mode ignores Unicode characters and provides a more performant implementation when you know the string contains only ASCII characters:

iex> String.downcase("OLÁ", :ascii)
"olÁ"

And :greek properly handles the context sensitive sigma in Greek:

iex> String.downcase("ΣΣ")
"σσ"

iex> String.downcase("ΣΣ", :greek)
"σς"

duplicate(subject, n)

duplicate(t(), non_neg_integer()) :: t()

Returns a string subject duplicated n times.

Inlined by the compiler.

Examples

iex> String.duplicate("abc", 0)
""

iex> String.duplicate("abc", 1)
"abc"

iex> String.duplicate("abc", 2)
"abcabc"

ends_with?(string, suffixes)

ends_with?(t(), t() | [t()]) :: boolean()

Returns true if string ends with any of the suffixes given.

suffixes can be either a single suffix or a list of suffixes.

Examples

iex> String.ends_with? "language", "age"
true
iex> String.ends_with? "language", ["youth", "age"]
true
iex> String.ends_with? "language", ["youth", "elixir"]
false

An empty suffix will always match:

iex> String.ends_with? "language", ""
true
iex> String.ends_with? "language", ["", "other"]
true

equivalent?(string1, string2)

equivalent?(t(), t()) :: boolean()

Returns true if string1 is canonically equivalent to ‘string2’.

It performs Normalization Form Canonical Decomposition (NFD) on the strings before comparing them. This function is equivalent to:

String.normalize(string1, :nfd) == String.normalize(string2, :nfd)

Therefore, if you plan to compare multiple strings, multiple times in a row, you may normalize them upfront and compare them directly to avoid multiple normalization passes.

Examples

iex> String.equivalent?("abc", "abc")
true

iex> String.equivalent?("man\u0303ana", "mañana")
true

iex> String.equivalent?("abc", "ABC")
false

iex> String.equivalent?("nø", "nó")
false

first(string)

first(t()) :: grapheme() | nil

Returns the first grapheme from a UTF-8 string, nil if the string is empty.

Examples

iex> String.first("elixir")
"e"

iex> String.first("եոգլի")
"ե"

graphemes(string)

graphemes(t()) :: [grapheme()]

Returns Unicode graphemes in the string as per Extended Grapheme Cluster algorithm.

The algorithm is outlined in the Unicode Standard Annex #29, Unicode Text Segmentation.

For details about codepoints and graphemes, see the String module documentation.

Examples

iex> String.graphemes("Ńaïve")
["Ń", "a", "ï", "v", "e"]

iex> String.graphemes("é")
["é"]

iex> String.graphemes("é")
["é"]

jaro_distance(string1, string2)

jaro_distance(t(), t()) :: float()

Returns a float value between 0 (equates to no similarity) and 1 (is an exact match) representing Jaro distance between string1 and string2.

The Jaro distance metric is designed and best suited for short strings such as person names.

Examples

iex> String.jaro_distance("dwayne", "duane")
0.8222222222222223
iex> String.jaro_distance("even", "odd")
0.0

last(string)

last(t()) :: grapheme() | nil

Returns the last grapheme from a UTF-8 string, nil if the string is empty.

Examples

iex> String.last("elixir")
"r"

iex> String.last("եոգլի")
"ի"

length(string)

length(t()) :: non_neg_integer()

Returns the number of Unicode graphemes in a UTF-8 string.

Examples

iex> String.length("elixir")
6

iex> String.length("եոգլի")
5

match?(string, regex)

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

Checks if string matches the given regular expression.

Examples

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

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

myers_difference(string1, string2)

myers_difference(t(), t()) :: [{:eq | :ins | :del, t()}] | nil

Returns a keyword list that represents an edit script.

Check List.myers_difference/2 for more information.

Examples

iex> string1 = "fox hops over the dog"
iex> string2 = "fox jumps over the lazy cat"
iex> String.myers_difference(string1, string2)
[eq: "fox ", del: "ho", ins: "jum", eq: "ps over the ", del: "dog", ins: "lazy cat"]

next_codepoint(string)

next_codepoint(t()) :: {codepoint(), t()} | nil

Returns the next codepoint in a string.

The result is a tuple with the codepoint and the remainder of the string or nil in case the string reached its end.

As with other functions in the String module, this function does not check for the validity of the codepoint. That said, if an invalid codepoint is found, it will be returned by this function.

Examples

iex> String.next_codepoint("olá")
{"o", "lá"}

next_grapheme(binary)

next_grapheme(t()) :: {grapheme(), t()} | nil

Returns the next grapheme in a string.

The result is a tuple with the grapheme and the remainder of the string or nil in case the String reached its end.

Examples

iex> String.next_grapheme("olá")
{"o", "lá"}

next_grapheme_size(string)

next_grapheme_size(t()) :: {pos_integer(), t()} | nil

Returns the size of the next grapheme.

The result is a tuple with the next grapheme size and the remainder of the string or nil in case the string reached its end.

Examples

iex> String.next_grapheme_size("olá")
{1, "lá"}

normalize(string, form)

normalize(t(), atom()) :: t()

Converts all characters in string to Unicode normalization form identified by form.

Forms

The supported forms are:

:nfd - Normalization Form Canonical Decomposition. Characters are decomposed by canonical equivalence, and multiple combining characters are arranged in a specific order.
:nfc - Normalization Form Canonical Composition. Characters are decomposed and then recomposed by canonical equivalence.

Examples

iex> String.normalize("yêṩ", :nfd)
"yêṩ"

iex> String.normalize("leña", :nfc)
"leña"

pad_leading(string, count, padding \\ [" "])

pad_leading(t(), non_neg_integer(), t() | [t()]) :: t()

Returns a new string padded with a leading filler which is made of elements from the padding.

Passing a list of strings as padding will take one element of the list for every missing entry. If the list is shorter than the number of inserts, the filling will start again from the beginning of the list. Passing a string padding is equivalent to passing the list of graphemes in it. If no padding is given, it defaults to whitespace.

When count is less than or equal to the length of string, given string is returned.

Raises ArgumentError if the given padding contains non-string element.

Examples

iex> String.pad_leading("abc", 5)
"  abc"

iex> String.pad_leading("abc", 4, "12")
"1abc"

iex> String.pad_leading("abc", 6, "12")
"121abc"

iex> String.pad_leading("abc", 5, ["1", "23"])
"123abc"

pad_trailing(string, count, padding \\ [" "])

pad_trailing(t(), non_neg_integer(), t() | [t()]) :: t()

Returns a new string padded with a trailing filler which is made of elements from the padding.

When count is less than or equal to the length of string, given string is returned.

Raises ArgumentError if the given padding contains non-string element.

Examples

iex> String.pad_trailing("abc", 5)
"abc  "

iex> String.pad_trailing("abc", 4, "12")
"abc1"

iex> String.pad_trailing("abc", 6, "12")
"abc121"

iex> String.pad_trailing("abc", 5, ["1", "23"])
"abc123"

printable?(string, counter \\ :infinity)

printable?(t(), non_neg_integer() | :infinity) :: boolean()

Checks if a string contains only printable characters.

Takes an optional limit as a second argument. printable?/2 only checks the printability of the string up to the limit.

Examples

iex> String.printable?("abc")
true

iex> String.printable?("abc" <> <<0>>)
false

iex> String.printable?("abc" <> <<0>>, 2)
true

replace(subject, pattern, replacement, options \\ [])

replace(t(), pattern() | Regex.t(), t(), keyword()) :: t()

Returns a new string created by replacing occurrences of pattern in subject with replacement.

The pattern may be a string or a regular expression.

By default it replaces all occurrences but this behaviour can be controlled through the :global option; see the “Options” section below.

Options

:global - (boolean) if true, all occurrences of pattern are replaced with replacement, otherwise only the first occurrence is replaced. Defaults to true
:insert_replaced - (integer or list of integers) specifies the position where to insert the replaced part inside the replacement. If any position given in the :insert_replaced option is larger than the replacement string, or is negative, an ArgumentError is raised. See the examples below

Examples

iex> String.replace("a,b,c", ",", "-")
"a-b-c"

iex> String.replace("a,b,c", ",", "-", global: false)
"a-b,c"

When the pattern is a regular expression, one can give \N or \g{N} in the replacement string to access a specific capture in the regular expression:

iex> String.replace("a,b,c", ~r/,(.)/, ",\\1\\g{1}")
"a,bb,cc"

Notice we had to escape the backslash escape character (i.e., we used \\N instead of just \N to escape the backslash; same thing for \\g{N}). By giving \0, one can inject the whole matched pattern in the replacement string.

When the pattern is a string, a developer can use the replaced part inside the replacement by using the :insert_replaced option and specifying the position(s) inside the replacement where the string pattern will be inserted:

iex> String.replace("a,b,c", "b", "[]", insert_replaced: 1)
"a,[b],c"

iex> String.replace("a,b,c", ",", "[]", insert_replaced: 2)
"a[],b[],c"

iex> String.replace("a,b,c", ",", "[]", insert_replaced: [1, 1])
"a[,,]b[,,]c"

When an empty string is provided as a pattern, the function will treat it as an implicit empty string between each grapheme and the string will be interspersed. If an empty string is provided as replacement the subject will be returned:

iex> String.replace("ELIXIR", "", ".")
".E.L.I.X.I.R."

iex> String.replace("ELIXIR", "", "")
"ELIXIR"

replace_leading(string, match, replacement)

replace_leading(t(), t(), t()) :: t() | no_return()

Replaces all leading occurrences of match by replacement of match in string.

Returns the string untouched if there are no occurrences.

If match is "", this function raises an ArgumentError exception: this happens because this function replaces all the occurrences of match at the beginning of string, and it’s impossible to replace “multiple” occurrences of "".

Examples

iex> String.replace_leading("hello world", "hello ", "")
"world"
iex> String.replace_leading("hello hello world", "hello ", "")
"world"

iex> String.replace_leading("hello world", "hello ", "ola ")
"ola world"
iex> String.replace_leading("hello hello world", "hello ", "ola ")
"ola ola world"

replace_prefix(string, match, replacement)

replace_prefix(t(), t(), t()) :: t()

Replaces prefix in string by replacement if it matches match.

Returns the string untouched if there is no match. If match is an empty string (""), replacement is just prepended to string.

Examples

iex> String.replace_prefix("world", "hello ", "")
"world"
iex> String.replace_prefix("hello world", "hello ", "")
"world"
iex> String.replace_prefix("hello hello world", "hello ", "")
"hello world"

iex> String.replace_prefix("world", "hello ", "ola ")
"world"
iex> String.replace_prefix("hello world", "hello ", "ola ")
"ola world"
iex> String.replace_prefix("hello hello world", "hello ", "ola ")
"ola hello world"

iex> String.replace_prefix("world", "", "hello ")
"hello world"

replace_suffix(string, match, replacement)

replace_suffix(t(), t(), t()) :: t()

Replaces suffix in string by replacement if it matches match.

Returns the string untouched if there is no match. If match is an empty string (""), replacement is just appended to string.

Examples

iex> String.replace_suffix("hello", " world", "")
"hello"
iex> String.replace_suffix("hello world", " world", "")
"hello"
iex> String.replace_suffix("hello world world", " world", "")
"hello world"

iex> String.replace_suffix("hello", " world", " mundo")
"hello"
iex> String.replace_suffix("hello world", " world", " mundo")
"hello mundo"
iex> String.replace_suffix("hello world world", " world", " mundo")
"hello world mundo"

iex> String.replace_suffix("hello", "", " world")
"hello world"

replace_trailing(string, match, replacement)

replace_trailing(t(), t(), t()) :: t() | no_return()

Replaces all trailing occurrences of match by replacement in string.

Returns the string untouched if there are no occurrences.

If match is "", this function raises an ArgumentError exception: this happens because this function replaces all the occurrences of match at the end of string, and it’s impossible to replace “multiple” occurrences of "".

Examples

iex> String.replace_trailing("hello world", " world", "")
"hello"
iex> String.replace_trailing("hello world world", " world", "")
"hello"

iex> String.replace_trailing("hello world", " world", " mundo")
"hello mundo"
iex> String.replace_trailing("hello world world", " world", " mundo")
"hello mundo mundo"

reverse(string)

reverse(t()) :: t()

Reverses the graphemes in given string.

Examples

iex> String.reverse("abcd")
"dcba"

iex> String.reverse("hello world")
"dlrow olleh"

iex> String.reverse("hello ∂og")
"go∂ olleh"

Keep in mind reversing the same string twice does not necessarily yield the original string:

iex> "̀e"
"̀e"
iex> String.reverse("̀e")
"è"
iex> String.reverse String.reverse("̀e")
"è"

In the first example the accent is before the vowel, so it is considered two graphemes. However, when you reverse it once, you have the vowel followed by the accent, which becomes one grapheme. Reversing it again will keep it as one single grapheme.

slice(string, range)

slice(t(), Range.t()) :: t()

Returns a substring from the offset given by the start of the range to the offset given by the end of the range.

If the start of the range is not a valid offset for the given string or if the range is in reverse order, returns "".

If the start or end of the range is negative, the whole string is traversed first in order to convert the negative indices into positive ones.

Remember this function works with Unicode graphemes and considers the slices to represent grapheme offsets. If you want to split on raw bytes, check Kernel.binary_part/3 instead.

Examples

iex> String.slice("elixir", 1..3)
"lix"

iex> String.slice("elixir", 1..10)
"lixir"

iex> String.slice("elixir", 10..3)
""

iex> String.slice("elixir", -4..-1)
"ixir"

iex> String.slice("elixir", 2..-1)
"ixir"

iex> String.slice("elixir", -4..6)
"ixir"

iex> String.slice("elixir", -1..-4)
""

iex> String.slice("elixir", -10..-7)
""

iex> String.slice("a", 0..1500)
"a"

iex> String.slice("a", 1..1500)
""

slice(string, start, len)

slice(t(), integer(), integer()) :: grapheme()

Returns a substring starting at the offset start, and of length len.

If the offset is greater than string length, then it returns "".

Remember this function works with Unicode graphemes and considers the slices to represent grapheme offsets. If you want to split on raw bytes, check Kernel.binary_part/3 instead.

Examples

iex> String.slice("elixir", 1, 3)
"lix"

iex> String.slice("elixir", 1, 10)
"lixir"

iex> String.slice("elixir", 10, 3)
""

iex> String.slice("elixir", -4, 4)
"ixir"

iex> String.slice("elixir", -10, 3)
""

iex> String.slice("a", 0, 1500)
"a"

iex> String.slice("a", 1, 1500)
""

iex> String.slice("a", 2, 1500)
""

split(binary)

split(t()) :: [t()]

Divides a string into substrings at each Unicode whitespace occurrence with leading and trailing whitespace ignored. Groups of whitespace are treated as a single occurrence. Divisions do not occur on non-breaking whitespace.

Examples

iex> String.split("foo bar")
["foo", "bar"]

iex> String.split("foo" <> <<194, 133>> <> "bar")
["foo", "bar"]

iex> String.split(" foo   bar ")
["foo", "bar"]

iex> String.split("no\u00a0break")
["no\u00a0break"]

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

split(t(), pattern() | Regex.t(), keyword()) :: [t()]

Divides a string into substrings based on a pattern.

Returns a list of these substrings. The pattern can be a string, a list of strings, or a regular expression.

The string is split into as many parts as possible by default, but can be controlled via the :parts option.

Empty strings are only removed from the result if the :trim option is set to true.

When the pattern used is a regular expression, the string is split using Regex.split/3.

Options

:parts (positive integer or :infinity) - the string is split into at most as many parts as this option specifies. If :infinity, the string will be split into all possible parts. Defaults to :infinity.
:trim (boolean) - if true, empty strings are removed from the resulting list.

This function also accepts all options accepted by Regex.split/3 if pattern is a regular expression.

Examples

Splitting with a string pattern:

iex> String.split("a,b,c", ",")
["a", "b", "c"]

iex> String.split("a,b,c", ",", parts: 2)
["a", "b,c"]

iex> String.split(" a b c ", " ", trim: true)
["a", "b", "c"]

A list of patterns:

iex> String.split("1,2 3,4", [" ", ","])
["1", "2", "3", "4"]

A regular expression:

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

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

iex> String.split(" a b c ", ~r{\s}, trim: true)
["a", "b", "c"]

iex> String.split("abc", ~r{b}, include_captures: true)
["a", "b", "c"]

Splitting on empty string returns graphemes:

iex> String.split("abc", "")
["", "a", "b", "c", ""]

iex> String.split("abc", "", trim: true)
["a", "b", "c"]

iex> String.split("abc", "", parts: 1)
["abc"]

iex> String.split("abc", "", parts: 3)
["", "a", "bc"]

A precompiled pattern can also be given:

iex> pattern = :binary.compile_pattern([" ", ","])
iex> String.split("1,2 3,4", pattern)
["1", "2", "3", "4"]

Note this function can split within or across grapheme boundaries. For example, take the grapheme “é” which is made of the characters “e” and the acute accent. The following returns true:

iex> String.split(String.normalize("é", :nfd), "e")
["", "́"]

However, if “é” is represented by the single character “e with acute” accent, then it will return false:

iex> String.split(String.normalize("é", :nfc), "e")
["é"]

split_at(string, position)

split_at(t(), integer()) :: {t(), t()}

Splits a string into two at the specified offset. When the offset given is negative, location is counted from the end of the string.

The offset is capped to the length of the string. Returns a tuple with two elements.

Note: keep in mind this function splits on graphemes and for such it has to linearly traverse the string. If you want to split a string or a binary based on the number of bytes, use Kernel.binary_part/3 instead.

Examples

iex> String.split_at "sweetelixir", 5
{"sweet", "elixir"}

iex> String.split_at "sweetelixir", -6
{"sweet", "elixir"}

iex> String.split_at "abc", 0
{"", "abc"}

iex> String.split_at "abc", 1000
{"abc", ""}

iex> String.split_at "abc", -1000
{"", "abc"}

splitter(string, pattern, options \\ [])

splitter(t(), pattern(), keyword()) :: Enumerable.t()

Returns an enumerable that splits a string on demand.

This is in contrast to split/3 which splits all the string upfront.

Note splitter does not support regular expressions (as it is often more efficient to have the regular expressions traverse the string at once than in multiple passes).

Options

:trim - when true, does not emit empty patterns

Examples

iex> String.splitter("1,2 3,4 5,6 7,8,...,99999", [" ", ","]) |> Enum.take(4)
["1", "2", "3", "4"]

iex> String.splitter("abcd", "") |> Enum.take(10)
["", "a", "b", "c", "d", ""]

iex> String.splitter("abcd", "", trim: true) |> Enum.take(10)
["a", "b", "c", "d"]

starts_with?(string, prefix)

starts_with?(t(), t() | [t()]) :: boolean()

Returns true if string starts with any of the prefixes given.

prefix can be either a single prefix or a list of prefixes.

Examples

iex> String.starts_with? "elixir", "eli"
true
iex> String.starts_with? "elixir", ["erlang", "elixir"]
true
iex> String.starts_with? "elixir", ["erlang", "ruby"]
false

An empty string will always match:

iex> String.starts_with? "elixir", ""
true
iex> String.starts_with? "elixir", ["", "other"]
true

to_atom(string)

to_atom(String.t()) :: atom()

Converts a string to an atom.

Warning: this function creates atoms dynamically and atoms are not garbage collected. Therefore, string should not be an untrusted value, such as input received from a socket or during a web request. Consider using to_existing_atom/1 instead.

By default, the maximum number of atoms is 1_048_576. This limit can be raised or lowered using the VM option +t.

The maximum atom size is of 255 characters. Prior to OTP 20, only latin1 characters are allowed.

Inlined by the compiler.

Examples

iex> String.to_atom("my_atom")
:my_atom

to_charlist(string)

to_charlist(t()) :: charlist()

Converts a string into a charlist.

Specifically, this functions takes a UTF-8 encoded binary and returns a list of its integer codepoints. It is similar to codepoints/1 except that the latter returns a list of codepoints as strings.

In case you need to work with bytes, take a look at the :binary module.

Examples

iex> String.to_charlist("æß")
'æß'

to_existing_atom(string)

to_existing_atom(String.t()) :: atom()

Converts a string to an existing atom.

The maximum atom size is of 255 characters. Prior to OTP 20, only latin1 characters are allowed.

Inlined by the compiler.

Examples

iex> _ = :my_atom
iex> String.to_existing_atom("my_atom")
:my_atom

iex> String.to_existing_atom("this_atom_will_never_exist")
** (ArgumentError) argument error

to_float(string)

to_float(String.t()) :: float()

Returns a float whose text representation is string.

string must be the string representation of a float including a decimal point. In order to parse a string without decimal point as a float then Float.parse/1 should be used. Otherwise, an ArgumentError will be raised.

Inlined by the compiler.

Examples

iex> String.to_float("2.2017764e+0")
2.2017764

iex> String.to_float("3.0")
3.0

String.to_float("3")
#=> ** (ArgumentError) argument error

to_integer(string)

to_integer(String.t()) :: integer()

Returns an integer whose text representation is string.

Inlined by the compiler.

Examples

iex> String.to_integer("123")
123

to_integer(string, base)

to_integer(String.t(), 2..36) :: integer()

Returns an integer whose text representation is string in base base.

Inlined by the compiler.

Examples

iex> String.to_integer("3FF", 16)
1023

trim(string)

trim(t()) :: t()

Returns a string where all leading and trailing Unicode whitespaces have been removed.

Examples

iex> String.trim("\n  abc\n  ")
"abc"

trim(string, to_trim)

trim(t(), t()) :: t()

Returns a string where all leading and trailing to_trims have been removed.

Examples

iex> String.trim("a  abc  a", "a")
"  abc  "

trim_leading(string)

trim_leading(t()) :: t()

Returns a string where all leading Unicode whitespaces have been removed.

Examples

iex> String.trim_leading("\n  abc   ")
"abc   "

trim_leading(string, to_trim)

trim_leading(t(), t()) :: t()

Returns a string where all leading to_trims have been removed.

Examples

iex> String.trim_leading("__ abc _", "_")
" abc _"

iex> String.trim_leading("1 abc", "11")
"1 abc"

trim_trailing(string)

trim_trailing(t()) :: t()

Returns a string where all trailing Unicode whitespaces has been removed.

Examples

iex> String.trim_trailing("   abc\n  ")
"   abc"

trim_trailing(string, to_trim)

trim_trailing(t(), t()) :: t()

Returns a string where all trailing to_trims have been removed.

Examples

iex> String.trim_trailing("_ abc __", "_")
"_ abc "

iex> String.trim_trailing("abc 1", "11")
"abc 1"

upcase(string, mode \\ :default)

upcase(t(), :default | :ascii | :greek) :: t()

Converts all characters in the given string to uppercase according to mode.

mode may be :default, :ascii or :greek. The :default mode considers all non-conditional transformations outlined in the Unicode standard. :ascii uppercases only the letters a to z. :greek includes the context sensitive mappings found in Greek.

Examples

iex> String.upcase("abcd")
"ABCD"

iex> String.upcase("ab 123 xpto")
"AB 123 XPTO"

iex> String.upcase("olá")
"OLÁ"

The :ascii mode ignores Unicode characters and provides a more performant implementation when you know the string contains only ASCII characters:

iex> String.upcase("olá", :ascii)
"OLá"

valid?(string)

valid?(t()) :: boolean()

Checks whether string contains only valid characters.

Examples

iex> String.valid?("a")
true

iex> String.valid?("ø")
true

iex> String.valid?(<<0xFFFF :: 16>>)
false

iex> String.valid?(<<0xEF, 0xB7, 0x90>>)
true

iex> String.valid?("asd" <> <<0xFFFF :: 16>>)
false