string
Module
Module Summary
Description
This module provides functions for string processing.
A string in this module is represented by unicode:chardata(), that is, a list of codepoints, binaries with UTF-8-encoded codepoints (UTF-8 binaries), or a mix of the two.
"abcd" is a valid string
<<"abcd">> is a valid string
["abcd"] is a valid string
<<"abc..åäö"/utf8>> is a valid string
<<"abc..åäö">> is NOT a valid string,
but a binary with Latin-1-encoded codepoints
[<<"abc">>, "..åäö"] is a valid string
[atom] is NOT a valid stringThis module operates on grapheme clusters. A grapheme cluster is a user-perceived character, which can be represented by several codepoints.
"å" [229] or [97, 778] "e̊" [101, 778]
The string length of "ß↑e̊" is 3, even though it is represented by the codepoints [223,8593,101,778] or the UTF-8 binary <<195,159,226,134,145,101,204,138>>.
Grapheme clusters for codepoints of class prepend and non-modern (or decomposed) Hangul is not handled for performance reasons in find/3, replace/3, split/2, split/2 and trim/3.
Splitting and appending strings is to be done on grapheme clusters borders. There is no verification that the results of appending strings are valid or normalized.
Most of the functions expect all input to be normalized to one form, see for example unicode:characters_to_nfc_list/1.
Language or locale specific handling of input is not considered in any function.
The functions can crash for non-valid input strings. For example, the functions expect UTF-8 binaries but not all functions verify that all binaries are encoded correctly.
Unless otherwise specified the return value type is the same as the input type. That is, binary input returns binary output, list input returns a list output, and mixed input can return a mixed output.
1> string:trim(" sarah ").
"sarah"
2> string:trim(<<" sarah ">>).
<<"sarah">>
3> string:lexemes("foo bar", " ").
["foo","bar"]
4> string:lexemes(<<"foo bar">>, " ").
[<<"foo">>,<<"bar">>]This module has been reworked in Erlang/OTP 20 to handle unicode:chardata() and operate on grapheme clusters. The old functions that only work on Latin-1 lists as input are kept for backwards compatibility reasons but should not be used.
Data Types
A user-perceived character, consisting of one or more codepoints.
Exports
Converts String to a case-agnostic comparable string. Function casefold/1 is preferred over lowercase/1 when two strings are to be compared for equality. See also equal/4.
Example:
1> string:casefold("Ω and ẞ SHARP S").
"ω and ss sharp s"
Returns a string where any trailing \n or \r\n have been removed from String.
Example:
182> string:chomp(<<"\nHello\n\n">>). <<"\nHello">> 183> string:chomp("\nHello\r\r\n"). "\nHello\r"
Returns true if A and B are equal, otherwise false.
If IgnoreCase is true the function does casefolding on the fly before the equality test.
If Norm is not none the function applies normalization on the fly before the equality test. There are four available normalization forms: nfc, nfd, nfkc, and nfkd.
By default, IgnoreCase is false and Norm is none.
Example:
1> string:equal("åäö", <<"åäö"/utf8>>). true 2> string:equal("åäö", unicode:characters_to_nfd_binary("åäö")). false 3> string:equal("åäö", unicode:characters_to_nfd_binary("ÅÄÖ"), true, nfc). true
Removes anything before SearchPattern in String and returns the remainder of the string or nomatch if SearchPattern is not found. Dir, which can be leading or trailing, indicates from which direction characters are to be searched.
By default, Dir is leading.
Example:
1> string:find("ab..cd..ef", "."). "..cd..ef" 2> string:find(<<"ab..cd..ef">>, "..", trailing). <<"..ef">> 3> string:find(<<"ab..cd..ef">>, "x", leading). nomatch 4> string:find("ab..cd..ef", "x", trailing). nomatch
Returns true if String is the empty string, otherwise false.
Example:
1> string:is_empty("foo"). false 2> string:is_empty(["",<<>>]). true
Returns the number of grapheme clusters in String.
Example:
1> string:length("ß↑e̊"). 3 2> string:length(<<195,159,226,134,145,101,204,138>>). 3
SeparatorList :: [grapheme_cluster()]) ->
[unicode:chardata()]
Returns a list of lexemes in String, separated by the grapheme clusters in SeparatorList.
Notice that, as shown in this example, two or more adjacent separator graphemes clusters in String are treated as one. That is, there are no empty strings in the resulting list of lexemes. See also split/3 which returns empty strings.
Notice that [$\r,$\n] is one grapheme cluster.
Example:
1> string:lexemes("abc de̊fxxghix jkl\r\nfoo", "x e" ++ [[$\r,$\n]]). ["abc","de̊f","ghi","jkl","foo"] 2> string:lexemes(<<"abc de̊fxxghix jkl\r\nfoo"/utf8>>, "x e" ++ [$\r,$\n]). [<<"abc">>,<<"de̊f"/utf8>>,<<"ghi">>,<<"jkl\r\nfoo">>]
Converts String to lowercase.
Notice that function casefold/1 should be used when converting a string to be tested for equality.
Example:
2> string:lowercase(string:uppercase("Michał")).
"michał"maybe_improper_list(char(), unicode:chardata()) |
{error, unicode:chardata()}
Returns the first codepoint in String and the rest of String in the tail. Returns an empty list if String is empty or an {error, String} tuple if the next byte is invalid.
Example:
1> string:next_codepoint(unicode:characters_to_binary("e̊fg")).
[101|<<"̊fg"/utf8>>]maybe_improper_list(grapheme_cluster(),
unicode:chardata()) |
{error, unicode:chardata()}
Returns the first grapheme cluster in String and the rest of String in the tail. Returns an empty list if String is empty or an {error, String} tuple if the next byte is invalid.
Example:
1> string:next_grapheme(unicode:characters_to_binary("e̊fg")).
["e̊"|<<"fg">>]
Returns lexeme number N in String, where lexemes are separated by the grapheme clusters in SeparatorList.
Example:
1> string:nth_lexeme("abc.de̊f.ghiejkl", 3, ".e").
"ghi"Types
Pads String to Length with grapheme cluster Char. Dir, which can be leading, trailing, or both, indicates where the padding should be added.
By default, Char is $\s and Dir is trailing.
Example:
1> string:pad(<<"He̊llö"/utf8>>, 8). [<<72,101,204,138,108,108,195,182>>,32,32,32] 2> io:format("'~ts'~n",[string:pad("He̊llö", 8, leading)]). ' He̊llö' 3> io:format("'~ts'~n",[string:pad("He̊llö", 8, both)]). ' He̊llö '
If Prefix is the prefix of String, removes it and returns the remainder of String, otherwise returns nomatch.
Example:
1> string:prefix(<<"prefix of string">>, "pre"). <<"fix of string">> 2> string:prefix("pre", "prefix"). nomatch
[unicode:chardata()]
[unicode:chardata()]
Replaces SearchPattern in String with Replacement. Where, default leading, indicates whether the leading, the trailing or all encounters of SearchPattern are to be replaced.
Can be implemented as:
lists:join(Replacement, split(String, SearchPattern, Where)).
Example:
1> string:replace(<<"ab..cd..ef">>, "..", "*"). [<<"ab">>,"*",<<"cd..ef">>] 2> string:replace(<<"ab..cd..ef">>, "..", "*", all). [<<"ab">>,"*",<<"cd">>,"*",<<"ef">>]
Returns the reverse list of the grapheme clusters in String.
Example:
1> Reverse = string:reverse(unicode:characters_to_nfd_binary("ÅÄÖ")). [[79,776],[65,776],[65,778]] 2> io:format("~ts~n",[Reverse]). ÖÄÅ
Types
Returns a substring of String of at most Length grapheme clusters, starting at position Start.
By default, Length is infinity.
Example:
1> string:slice(<<"He̊llö Wörld"/utf8>>, 4). <<"ö Wörld"/utf8>> 2> string:slice(["He̊llö ", <<"Wörld"/utf8>>], 4,4). "ö Wö" 3> string:slice(["He̊llö ", <<"Wörld"/utf8>>], 4,50). "ö Wörld"
Splits String where SearchPattern is encountered and return the remaining parts. Where, default leading, indicates whether the leading, the trailing or all encounters of SearchPattern will split String.
Example:
0> string:split("ab..bc..cd", ".."). ["ab","bc..cd"] 1> string:split(<<"ab..bc..cd">>, "..", trailing). [<<"ab..bc">>,<<"cd">>] 2> string:split(<<"ab..bc....cd">>, "..", all). [<<"ab">>,<<"bc">>,<<>>,<<"cd">>]
Types
Takes characters from String as long as the characters are members of set Characters or the complement of set Characters. Dir, which can be leading or trailing, indicates from which direction characters are to be taken.
Example:
5> string:take("abc0z123", lists:seq($a,$z)). {"abc","0z123"} 6> string:take(<<"abc0z123">>, lists:seq($0,$9), true, leading). {<<"abc">>,<<"0z123">>} 7> string:take("abc0z123", lists:seq($0,$9), false, trailing). {"abc0z","123"} 8> string:take(<<"abc0z123">>, lists:seq($a,$z), true, trailing). {<<"abc0z">>,<<"123">>}
Converts String to titlecase.
Example:
1> string:titlecase("ß is a SHARP s").
"Ss is a SHARP s"Types
Argument String is expected to start with a valid text represented float (the digits are ASCII values). Remaining characters in the string after the float are returned in Rest.
Example:
> {F1,Fs} = string:to_float("1.0-1.0e-1"), > {F2,[]} = string:to_float(Fs), > F1+F2. 0.9 > string:to_float("3/2=1.5"). {error,no_float} > string:to_float("-1.5eX"). {-1.5,"eX"}
Types
Argument String is expected to start with a valid text represented integer (the digits are ASCII values). Remaining characters in the string after the integer are returned in Rest.
Example:
> {I1,Is} = string:to_integer("33+22"), > {I2,[]} = string:to_integer(Is), > I1-I2. 11 > string:to_integer("0.5"). {0,".5"} > string:to_integer("x=2"). {error,no_integer}
Converts String to a list of grapheme clusters.
Example:
1> string:to_graphemes("ß↑e̊"). [223,8593,[101,778]] 2> string:to_graphemes(<<"ß↑e̊"/utf8>>). [223,8593,[101,778]]
Returns a string, where leading or trailing, or both, Characters have been removed. Dir which can be leading, trailing, or both, indicates from which direction characters are to be removed.
Default Characters is the set of nonbreakable whitespace codepoints, defined as Pattern_White_Space in Unicode Standard Annex #31. By default, Dir is both.
Notice that [$\r,$\n] is one grapheme cluster according to the Unicode Standard.
Example:
1> string:trim("\t Hello \n"). "Hello" 2> string:trim(<<"\t Hello \n">>, leading). <<"Hello \n">> 3> string:trim(<<".Hello.\n">>, trailing, "\n."). <<".Hello">>
Converts String to uppercase.
See also titlecase/1.
Example:
1> string:uppercase("Michał").
"MICHAŁ"