Elixir v1.9.2 String View Source
A String in Elixir is a UTF-8 encoded binary.
Code points and grapheme cluster
The functions in this module act according to the Unicode Standard, version 11.0.0.
As per the standard, a code point is a single Unicode Character, which may be represented by one or more bytes.
For example, the code point "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 code points that may be perceived as a single character by readers. For example, "é" can be represented either as a single "e with acute" code point or as the letter "e" followed by a "combining acute accent" (two code points):
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 code points.
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 binaryKernel.bit_size/1
andKernel.byte_size/1
- size related functionsKernel.is_bitstring/1
andKernel.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 code point 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
code point into multiple bytes.
Integer code points
Although code points could be represented as integers, this module represents all code points as strings. For example:
iex> String.codepoints("olá")
["o", "l", "á"]
There are a couple of ways to retrieve a character integer
code point. 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, code points 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 code point 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 code point 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 strings 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 that the compiled pattern cannot be stored in a module attribute as the pattern is generated at runtime and does not survive compile time.
Link to this section Summary
Types
A UTF-8 code point. It may be one or more bytes.
Multiple code points that may be perceived as a single character by readers
A UTF-8 encoded binary.
Functions
Returns the grapheme at the position
of the given UTF-8 string
.
If position
is greater than string
length, then it returns nil
.
Computes the bag distance between two strings.
Converts the first character in the given string to
uppercase and the remainder to lowercase according to mode
.
Splits the string into chunks of characters that share a common trait.
Returns all code points in the string.
Checks if string
contains any of the given contents
.
Converts all characters in the given string to lowercase according to mode
.
Returns a string subject
duplicated n
times.
Returns true
if string
ends with any of the suffixes given.
Returns true
if string1
is canonically equivalent to 'string2'.
Returns the first grapheme from a UTF-8 string,
nil
if the string is empty.
Returns Unicode graphemes in the string as per Extended Grapheme Cluster algorithm.
Computes the Jaro distance (similarity) between two strings.
Returns the last grapheme from a UTF-8 string,
nil
if the string is empty.
Returns the number of Unicode graphemes in a UTF-8 string.
Checks if string
matches the given regular expression.
Returns a keyword list that represents an edit script.
Returns the next code point in a string.
Returns the next grapheme in a string.
Returns the size of the next grapheme.
Converts all characters in string
to Unicode normalization
form identified by form
.
Returns a new string padded with a leading filler
which is made of elements from the padding
.
Returns a new string padded with a trailing filler
which is made of elements from the padding
.
Checks if a string contains only printable characters up to character_limit
.
Returns a new string created by replacing occurrences of pattern
in
subject
with replacement
.
Replaces all leading occurrences of match
by replacement
of match
in string
.
Replaces prefix in string
by replacement
if it matches match
.
Replaces suffix in string
by replacement
if it matches match
.
Replaces all trailing occurrences of match
by replacement
in string
.
Reverses the graphemes in given string.
Returns a substring from the offset given by the start of the range to the offset given by the end of the range.
Returns a substring starting at the offset start
, and of
length len
.
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.
Divides a string into parts based on a pattern.
Splits a string into two at the specified offset. When the offset given is negative, location is counted from the end of the string.
Returns an enumerable that splits a string on demand.
Returns true
if string
starts with any of the prefixes given.
Converts a string to an atom.
Converts a string into a charlist.
Converts a string to an existing atom.
Returns a float whose text representation is string
.
Returns an integer whose text representation is string
.
Returns an integer whose text representation is string
in base base
.
Returns a string where all leading and trailing Unicode whitespaces have been removed.
Returns a string where all leading and trailing to_trim
characters have been
removed.
Returns a string where all leading Unicode whitespaces have been removed.
Returns a string where all leading to_trim
characters have been removed.
Returns a string where all trailing Unicode whitespaces has been removed.
Returns a string where all trailing to_trim
characters have been removed.
Converts all characters in the given string to uppercase according to mode
.
Checks whether string
contains only valid characters.
Link to this section Types
Specs
codepoint() :: t()
A UTF-8 code point. It may be one or more bytes.
Specs
grapheme() :: t()
Multiple code points that may be perceived as a single character by readers
Specs
pattern() :: t() | [t()] | :binary.cp()
Specs
t() :: binary()
A UTF-8 encoded binary.
The types String.t()
and binary()
are equivalent to analysis tools.
Although, for those reading the documentation, String.t()
implies
it is a UTF-8 encoded binary.
Link to this section Functions
Specs
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
Specs
Computes the bag distance between two strings.
Returns a float value between 0 and 1 representing the bag
distance between string1
and string2
.
The bag distance is meant to be an efficient approximation of the distance between two strings to quickly rule out strings that are largely different.
The algorithm is outlined in the "String Matching with Metric Trees Using an Approximate Distance" paper by Ilaria Bartolini, Paolo Ciaccia, and Marco Patella.
Examples
iex> String.bag_distance("abc", "")
0.0
iex> String.bag_distance("abcd", "a")
0.25
iex> String.bag_distance("abcd", "ab")
0.5
iex> String.bag_distance("abcd", "abc")
0.75
iex> String.bag_distance("abcd", "abcd")
1.0
Specs
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"
Specs
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>>]
Specs
Returns all code points in the string.
For details about code points 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", "́"]
Specs
Checks if string
contains any of the given contents
.
contents
can be either a string, a list of strings,
or a compiled pattern.
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
The argument can also be a compiled pattern:
iex> pattern = :binary.compile_pattern(["life", "death"])
iex> String.contains?("elixir of life", pattern)
true
An empty string will always match:
iex> String.contains?("elixir of life", "")
true
iex> String.contains?("elixir of life", ["", "other"])
true
Be aware that 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?(:unicode.characters_to_nfd_binary("é"), "e")
true
However, if "é" is represented by the single character "e with acute"
accent, then it will return false
:
iex> String.contains?(:unicode.characters_to_nfc_binary("é"), "e")
false
Specs
Converts all characters in the given string 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.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"
Specs
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"
Specs
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
Specs
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
Specs
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"
Specs
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 code points and graphemes, see the String
module documentation.
Examples
iex> String.graphemes("Ńaïve")
["Ń", "a", "ï", "v", "e"]
iex> String.graphemes("\u00e9")
["é"]
iex> String.graphemes("\u0065\u0301")
["é"]
Specs
Computes the Jaro distance (similarity) between two strings.
Returns a float value between 0.0
(equates to no similarity) and 1.0
(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. Elixir itself uses this function
to provide the "did you mean?" functionality. For instance, when you
are calling a function in a module and you have a typo in the
function name, we attempt to suggest the most similar function
name available, if any, based on the jaro_distance/2
score.
Examples
iex> String.jaro_distance("Dwayne", "Duane")
0.8222222222222223
iex> String.jaro_distance("even", "odd")
0.0
iex> String.jaro_distance("same", "same")
1.0
Specs
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"
Specs
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
Specs
Checks if string
matches the given regular expression.
Examples
iex> String.match?("foo", ~r/foo/)
true
iex> String.match?("bar", ~r/foo/)
false
Specs
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"]
Specs
Returns the next code point in a string.
The result is a tuple with the code point and the
remainder of the string or nil
in case
the string reached its end.
As with other functions in the String
module, next_codepoint/1
works with binaries that are invalid UTF-8. If the string starts
with a sequence of bytes that is not valid in UTF-8 encoding, the
first element of the returned tuple is a binary with the first byte.
Examples
iex> String.next_codepoint("olá")
{"o", "lá"}
iex> invalid = "\x80\x80OK" # first two bytes are invalid in UTF-8
iex> {_, rest} = String.next_codepoint(invalid)
{<<128>>, <<128, 79, 75>>}
iex> String.next_codepoint(rest)
{<<128>>, "OK"}
Comparison with binary pattern matching
Binary pattern matching provides a similar way to decompose a string:
iex> <<codepoint::utf8, rest::binary>> = "Elixir"
"Elixir"
iex> codepoint
69
iex> rest
"lixir"
though not entirely equivalent because codepoint
comes as
an integer, and the pattern won't match invalid UTF-8.
Binary pattern matching, however, is simpler and more efficient, so pick the option that better suits your use case.
Specs
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"}
Specs
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"}
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"
Specs
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 a 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"
Specs
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
.
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 a 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"
Specs
printable?(t(), 0) :: true
printable?(t(), pos_integer() | :infinity) :: boolean()
Checks if a string contains only printable characters up to character_limit
.
Takes an optional character_limit
as a second argument. If character_limit
is 0
, this
function will return true
.
Examples
iex> String.printable?("abc")
true
iex> String.printable?("abc" <> <<0>>)
false
iex> String.printable?("abc" <> <<0>>, 2)
true
iex> String.printable?("abc" <> <<0>>, 0)
true
Specs
Returns a new string created by replacing occurrences of pattern
in
subject
with replacement
.
The subject
is always a string.
The pattern
may be a string, a regular expression, or a compiled pattern.
The replacement
may be a string or a function that receives the matched
pattern and must return the replacement as a string or iodata.
By default it replaces all occurrences but this behaviour can be controlled
through the :global
option; see the "Options" section below.
Options
:global
- (boolean) iftrue
, all occurrences ofpattern
are replaced withreplacement
, otherwise only the first occurrence is replaced. Defaults totrue
Examples
iex> String.replace("a,b,c", ",", "-")
"a-b-c"
iex> String.replace("a,b,c", ",", "-", global: false)
"a-b,c"
The pattern may also be a list of strings and the replacement may also be a function that receives the matched patterns:
iex> String.replace("a,b,c", ["a", "c"], fn <<char>> -> <<char + 1>> end)
"b,b,d"
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.
A compiled pattern can also be given:
iex> pattern = :binary.compile_pattern(",")
iex> String.replace("a,b,c", pattern, "[]")
"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"
Specs
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"
Specs
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"
Specs
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"
Specs
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"
Specs
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.
Specs
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)
""
Specs
slice(t(), integer(), non_neg_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)
""
Specs
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"]
Specs
Divides a string into parts based on a pattern.
Returns a list of these parts. The pattern can be a string, a list of strings, a regular expression, or a compiled pattern.
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) - iftrue
, 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"]
A compiled pattern:
iex> pattern = :binary.compile_pattern([" ", ","])
iex> String.split("1,2 3,4", pattern)
["1", "2", "3", "4"]
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"]
Be aware that 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 will split the string into two parts:
iex> String.split(String.normalize("é", :nfd), "e")
["", "́"]
However, if "é" is represented by the single character "e with acute" accent, then it will split the string into just one part:
iex> String.split(String.normalize("é", :nfc), "e")
["é"]
Specs
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"}
Specs
splitter(t(), pattern(), keyword()) :: Enumerable.t()
Returns an enumerable that splits a string on demand.
This is in contrast to split/3
which splits the
entire string upfront.
This function does not support regular expressions by design. When using regular expressions, it is often more efficient to have the regular expressions traverse the string at once than in parts, like this function does.
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"]
A compiled pattern can also be given:
iex> pattern = :binary.compile_pattern([" ", ","])
iex> String.splitter("1,2 3,4 5,6 7,8,...,99999", pattern) |> Enum.take(4)
["1", "2", "3", "4"]
Specs
Returns true
if string
starts with any of the prefixes given.
prefix
can be either a string, a list of strings, or a compiled
pattern.
Examples
iex> String.starts_with?("elixir", "eli")
true
iex> String.starts_with?("elixir", ["erlang", "elixir"])
true
iex> String.starts_with?("elixir", ["erlang", "ruby"])
false
A compiled pattern can also be given:
iex> pattern = :binary.compile_pattern(["erlang", "elixir"])
iex> String.starts_with?("elixir", pattern)
true
An empty string will always match:
iex> String.starts_with?("elixir", "")
true
iex> String.starts_with?("elixir", ["", "other"])
true
Specs
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 Unicode code points.
Inlined by the compiler.
Examples
iex> String.to_atom("my_atom")
:my_atom
Specs
Converts a string into a charlist.
Specifically, this function takes a UTF-8 encoded binary and returns a list of its integer
code points. It is similar to codepoints/1
except that the latter returns a list of code points as
strings.
In case you need to work with bytes, take a look at the
:binary
module.
Examples
iex> String.to_charlist("æß")
'æß'
Specs
Converts a string to an existing atom.
The maximum atom size is of 255 Unicode code points.
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
Specs
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
Specs
Returns an integer whose text representation is string
.
string
must be the string representation of an integer.
Otherwise, an ArgumentError
will be raised. If you want
to parse a string that may contain an ill-formatted integer,
use Integer.parse/1
.
Inlined by the compiler.
Examples
iex> String.to_integer("123")
123
Passing a string that does not represent an integer leads to an error:
String.to_integer("invalid data")
#=> ** (ArgumentError) argument error
Specs
Returns an integer whose text representation is string
in base base
.
Inlined by the compiler.
Examples
iex> String.to_integer("3FF", 16)
1023
Specs
Returns a string where all leading and trailing Unicode whitespaces have been removed.
Examples
iex> String.trim("\n abc\n ")
"abc"
Specs
Returns a string where all leading and trailing to_trim
characters have been
removed.
Examples
iex> String.trim("a abc a", "a")
" abc "
Specs
Returns a string where all leading Unicode whitespaces have been removed.
Examples
iex> String.trim_leading("\n abc ")
"abc "
Specs
Returns a string where all leading to_trim
characters have been removed.
Examples
iex> String.trim_leading("__ abc _", "_")
" abc _"
iex> String.trim_leading("1 abc", "11")
"1 abc"
Specs
Returns a string where all trailing Unicode whitespaces has been removed.
Examples
iex> String.trim_trailing(" abc\n ")
" abc"
Specs
Returns a string where all trailing to_trim
characters have been removed.
Examples
iex> String.trim_trailing("_ abc __", "_")
"_ abc "
iex> String.trim_trailing("abc 1", "11")
"abc 1"
Specs
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"
Specs
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