String Functions

string.byte, utf8.byte

string.byte(string [, i [, j]]) or utf8.byte(string [, i [, j]])
mystring:byte([, i [, j]]): Returns the internal numerical codes of the characters s[i], s[i+1], ···, s[j]. The default value for i is 1; the default value for j is i.; Note that numerical codes are not necessarily portable across platforms.; string.byte() works with English text only, use utf8.byte() for the international version.; See also: string.char, utf8.char

Example

-- the following call will return the ASCII values of "A", "B" and "C"
a, b, c = string.byte("ABC", 1, 3)
echo(a .. " - " .. b .. " - " .. c) -- shows "65 - 66 - 67"

-- same for the international version but with the Unicode values
a, b, c = utf8.byte("дом", 1, 3)
echo(a .. " - " .. b .. " - " .. c) -- shows "1076 - 1086 - 1084"

string.char, utf8.char

string.char(···) or utf8.char(···): Receives zero or more integers. Returns a string with length equal to the number of arguments, in which each character has the internal numerical code equal to its corresponding argument.; Note that numerical codes are not necessarily portable across platforms.; string.char() works with English text only, use utf8.char() for the international version.; See also: string.byte, utf8.byte

Example

-- the following call will return the string "ABC" corresponding to the ASCII values 65, 66, 67
mystring = string.char(65, 66, 67)

-- same for the infernational version which will return text "дом" for the Unicode values 1076, 1086, 1084
mystring = utf8.char(1076,1086,1084)
print(mystring)

string.cut

string.cut(string, maxLen): Cuts string to the specified maximum length.; Returns the modified string.

Parameters

string:

The text you wish to cut. Passed as a string.

maxLen:

The maximum length you wish the string to be. Passed as an integer number.

Example

--The following call will return 'abc' and store it in myString
myString = string.cut("abcde", 3)
--You can easily pad string to certain length. Example below will print 'abcde     ' e.g. pad/cut string to 10 characters.
local s = "abcde"
s = string.cut(s .. "          ", 10)   -- append 10 spaces
echo("'" .. s .. "'")

string.dump

string.dump()

Converts a function into a binary string. You can use the loadstring() function later to get the function back.

string.dump() works with both English and non-English text fine.
Example

string = string.dump(echo("this is a string"))
--The following should then echo "this is a string"
loadstring(string)()

string.enclose

string.enclose(String): Wraps a string with [[ ]]; Returns the altered string.

Parameters

String:

The string to enclose. Passed as a string.

Example

--This will echo '[[Oh noes!]]' to the main window
echo("'" .. string.enclose("Oh noes!") .. "'")

string.ends

string.ends(String, Suffix): Test if string is ending with specified suffix.; Returns true or false.; See also: string.starts

Parameters

String:

The string to test. Passed as a string.

Suffix:

The suffix to test for. Passed as a string.

Example

--This will test if the incoming line ends with "in bed" and if not will add it to the end.
if not string.ends(line, "in bed") then
  echo("in bed\n")
end

string.find, utf8.find

string.find(text, pattern [, init [, plain]]) or utf8.find: Looks for the first match of pattern in the string text. If it finds a match, then find returns the indices of text where this occurrence starts and ends; otherwise, it returns nil. A third, optional numerical argument init specifies where to start the search; its default value is 1 and can be negative. A value of true as a fourth, optional argument plain turns off the pattern matching facilities, so the function does a plain "find substring" operation, with no characters in pattern being considered "magic". Note that if plain is given, then init must be given as well.

If the pattern has captures, then in a successful match the captured values are also returned, after the two indices.

string.find() works with English text only, use utf8.find() for the international version.
Example

The following example will print: "3, 4"

local start, stop = string.find("This is a test.", "is")
if start then
   print(start .. ", " .. stop)
end

Note that here "is" is being found at the end of the word "This", rather than the expected second word.

Return value:

nil or start and stop position of the first matched text, followed by any captured text.

string.findPattern

string.findPattern(text, pattern): Return first matching substring or nil.

Parameters

text:

The text you are searching the pattern for.

pattern:

The pattern you are trying to find in the text.

Example

Following example will print: "I did find: Troll" string.

local match = string.findPattern("Troll is here!", "Troll")
if match then
   echo("I did find: " .. match)
end

This example will find substring regardless of case.

local match = string.findPattern("Troll is here!", string.genNocasePattern("troll"))
if match then
    echo("I did find: " .. match)
end

Return value:

nil or first matching substring

string.format

string.format(formatstring,...): Returns a formatted version of its variable number of arguments following the description given in its first argument (which must be a string). The format string follows the same rules as the printf family of standard C functions. The only differences are that the options/modifiers *, l, L, n, p, and h are not supported and that there is an extra option, q. The q option formats a string in a form suitable to be safely read back by the Lua interpreter: the string is written between double quotes, and all double quotes, newlines, embedded zeros, and backslashes in the string are correctly escaped when written. For instance, the call

    string.format('%q', 'a string with "quotes" and \n new line')

will produce the string:

    "a string with \"quotes\" and \
     new line"

The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a number as argument, whereas q and s expect a string.

This function does not accept string values containing embedded zeros, except as arguments to the q option.

string.format() works with both English and non-English text fine.
Example

Need example

string.genNocasePattern

string.genNocasePattern(s): Generate case insensitive search pattern from string.

Parameters

s:

Example: Following example will generate and print "123[aA][bB][cC]" string.

echo(string.genNocasePattern("123abc"))

Return value:

case insensitive pattern string

string.gfind

string.gfind(): This is an old version of what is now string.gmatch. Use string.gmatch instead.
Example

Need example

string.gmatch, utf8.gmatch

string.gmatch(text, pattern) or utf8.gmatch: Returns an iterator function that, each time it is called, returns the next captures from pattern over string text. If pattern specifies no captures, then the whole match is produced in each call.

As an example, the following loop

    s = "hello world from Lua"
    for w in string.gmatch(s, "%a+") do
      print(w)
    end

will iterate over all the words from string s, printing one per line. The next example collects all pairs key=value from the given string into a table:

    t = {}
    s = "from=world, to=Lua"
    for k, v in string.gmatch(s, "(%w+)=(%w+)") do
      t[k] = v
    end

For this function, a '^' at the start of a pattern does not work as an anchor, as this would prevent the iteration.

string.gmatch() works with English text only, use utf8.gmatch() for the international version.
Example

Need example

string.gsub, utf8.gsub

string.gsub(text, pattern, repl [, n]) or utf8.gsub: Returns a copy of text in which all (or the first n, if given) occurrences of the pattern have been replaced by a replacement string specified by repl, which can be a string, a table, or a function. gsub also returns, as its second value, the total number of matches that occurred.

If repl is a string, then its value is used for replacement. The character % works as an escape character: any sequence in repl of the form %n, with n between 1 and 9, stands for the value of the n-th captured substring (see below). The sequence %0 stands for the whole match. The sequence %% stands for a single %.

If repl is a table, then the table is queried for every match, using the first capture as the key; if the pattern specifies no captures, then the whole match is used as the key.

If repl is a function, then this function is called every time a match occurs, with all captured substrings passed as arguments, in order; if the pattern specifies no captures, then the whole match is passed as a sole argument.

If the value returned by the table query or by the function call is a string or a number, then it is used as the replacement string; otherwise, if it is false or nil, then there is no replacement (that is, the original match is kept in the string).

string.gsub() works with English text only, use utf8.gsub() for the international version.
Example

     x = string.gsub("hello world", "(%w+)", "%1 %1")
     --> x="hello hello world world"
     
     x = string.gsub("hello world", "%w+", "%0 %0", 1)
     --> x="hello hello world"
     
     x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
     --> x="world hello Lua from"
     
     x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
     --> x="home = /home/roberto, user = roberto"
     
     x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
           return loadstring(s)()
         end)
     --> x="4+5 = 9"
     
     local t = {name="lua", version="5.1"}
     x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
     --> x="lua-5.1.tar.gz"

string.len, utf8.len

string.len(string) or utf8.len(string)
mystring:len(): Receives a string and returns its length. The empty string "" has length 0. Embedded zeros are counted, so "a\000bc\000" has length 5.; string.len() works with English text only, use utf8.len() for the international version.

Parameters

string:

The string (text) you want to find the length of.

Example

-- prints 5 for the 5 letters in our word
print(string.len("hello"))

-- international version
print(utf8.len("слово"))

string.lower, utf8.lower

string.lower(string) or utf8.lower(string)
mystring:lower(): Receives a string and returns a copy of this string with all uppercase letters changed to lowercase. All other characters are left unchanged. The definition of what an uppercase letter is depends on the current locale.; string.lower() works with English text only, use utf8.lower() for the international version.; See also: string.upper, utf8.upper

Example

-- prints an all-lowercase version
print(string.lower("No way! This is AWESOME!"))

-- international version
print(utf8.lower("Класс! Ето ОТЛИЧНО!"))

string.match, utf8.match

string.match() or utf8.match(): Need description here.; string.match() works with English text only, use utf8.match() for the international version.
Example

Need example

string.rep

string.rep(String, n)
mystring:rep(n): Returns a string that is the concatenation of n copies of the string String.; string.rep() works with both English and non-English text fine.

Example

Need example

string.reverse, utf8.reverse

string.reverse(string), utf8.reverse(string)
mystring:reverse()

Returns a string that is the string string reversed.

string.reverse() works with English text only, use utf8.reverse() for the international version.

Parameters

string:

The string to reverse. Passed as a string.

Example

mystring = "Hello from Lua"
echo(mystring:reverse()) -- displays 'auL morf olleH'

-- international version.
mystring = "Привет от Луа!"
echo(utf8.reverse(mystring)) -- displays '!ауЛ то тевирП', which probably looks the same to you

string.split

string.split(string, delimiter)
myString:split(delimiter): Splits a string into a table by the given delimiter. Can be called against a string (or variable holding a string) using the second form above.; Returns a table containing the split sections of the string.

Parameters

string:

The string to split. Parameter is not needed if using second form of the syntax above. Passed as a string.

delimiter:

The delimiter to use when splitting the string. Passed as a string, and allows for Lua pattern types. Use % to escape here (and %% to escape a stand-alone %).

Example

-- This will split the string by ", " delimiter and print the resulting table to the main window.
names = "Alice, Bob, Peter"
name_table = string.split(names, ", ")
display(name_table)

--The alternate method
names = "Alice, Bob, Peter"
name_table = names:split(", ")
display(name_table)

Either method above will print out:

table {

1: 'Alice'

2: 'Bob'

3: 'Peter'

}

string.starts

string.starts(string, prefix): Test if string is starting with specified prefix.; Returns true or false; See also: string.ends

Parameters

string:

The string to test. Passed as a string.

prefix:

The prefix to test for. Passed as a string.

Example

--The following will see if the line begins with "You" and if so will print a statement at the end of the line
if string.starts(line, "You") then
  echo("====oh you====\n")
end

string.sub, utf8.sub

string.sub() or utf8.sub(): Need description here.; string.sub() works with English text only, use utf8.sub() for the international version.
Example

Need example

string.title

string.title(string)
string:title(): Capitalizes the first character in a string.; Returns the altered string.

Parameters

string:

The string to modify. Not needed if you use the second form of the syntax above.

Example

--Variable testname is now Anna.
testname = string.title("anna")
--Example will set test to "Bob".
test = "bob"
test = test:title()

string.trim

string.trim(string): Trims string, removing all 'extra' white space at the beginning and end of the text.; Returns the altered string.

Parameters

string:

The string to trim. Passed as a string.

Example

--This will print 'Troll is here!', without the extra spaces.
local str = string.trim("  Troll is here!  ")
echo("'" .. str .. "'")

string.upper, utf8.upper

string.upper(string) or utf8.upper(string)
mystring:upper(): Receives a string and returns a copy of this string with all lowercase letters changed to uppercase. All other characters are left unchanged. The definition of what a lowercase letter is depends on the current locale.; string.upper() works with English text only, use utf8.upper() for the international version.

utf8.charpos

utf8.charpos(string[[, charpos], offset]): Converts UTF-8 position to byte offset, returns the character position and code point. If only offset is given, returns byte offset of this UTF-8 char index. If charpos and offset is given, a new charpos will be calculated by adding/subtracting UTF-8 char offset to current charpos. In all cases, it return a new char position, and code point (a number) at this position.

Parameters

string:

The input string to work on.

charpos:

(optional) character position to work on.

offset:

(optional) offset (as a number) to work on.

utf8.escape

utf8.escape(string): Escape a string to UTF-8 format string. It support several escape formats:

%ddd - which ddd is a decimal number at any length:

      change Unicode code point to UTF-8 format.

%{ddd} - same as %nnn but has bracket around. %uddd - same as %ddd, u stands Unicode %u{ddd} - same as %{ddd} %xhhh - hexadigit version of %ddd %x{hhh} same as %xhhh. %? - '?' stands for any other character: escape this character.

Parameters

string:

The string you want to escape

Example

local u = utf8.escape
print(u"%123%u123%{123}%u{123}%xABC%x{ABC}")
print(u"%%123%?%d%%u")

utf8.fold

utf8.fold(string): Returns the lowercase version of the string for use in case-insensitive comparisons. If string is a number, it's treated as a code point and the converted code point is returned (as a number).

Parameters

string:

The string to lowercase.

Example

print(utf8.fold("ПРИВЕТ")) -- 'привет'
print(utf8.fold("Привет")) -- 'привет'

utf8.insert

utf8.insert(string[, idx], substring): Inserts the substring into the given string. If idx is given, inserts substring before the character at this index, otherwise the substring will append onto the end of string. idx can be negative.

Parameters

string:

The input string to work on.

idx:

(optional) character position to insert the string at.

substring:

text to insert into the substring.

Example

-- inserts letter я before the 2nd letter and prints 'мясо'
print(utf8.insert("мсо", 2, "я"))

utf8.ncasecmp

utf8.ncasecmp(a, b): Compares a and b without case. Return -1 means a < b, 0 means a == b and 1 means a > b.

Parameters

a:

String to compare.

b:

String to compare against.

utf8.next

utf8.next(string[, charpos[, offset]]): Iterates though the UTF-8 string.

Parameters

string:

The input string to work on.

charpos:

(optional) character position to work on.

offset:

(optional) offset (as a number) to work on.

Example

-- prints location and code point of every letter
for pos, code in utf8.next, "тут есть текст" do
   print(pos, code)
end

utf8.remove

utf8.remove(string[, start[, stop]]): Removed characters from the given string. Deletes characters from the given start to the end of the string. If stop is given, deletes characters from start to stop (including start and stop). start and stop can be negative.

Parameters

string:

The input string to work on.

start:

position to start deleting characters from.

stop:

(optional) posititon to stop deleting characters at.

Example

-- delete everything from the 3rd character including the character itself
print(utf8.remove("мясо", 3)) -- 'мя'

-- delete the last character, use negative to count backwards
print(utf8.remove("мясо", -1)) -- 'мяс'

-- delete everything from the 2nd to the 4th character
print(utf8.remove("вкусное", 2,4)) -- 'вное'

utf8.title

utf8.title(string): Returns the uppercase version of the string for use in case-insensitive comparisons. If string is a number, it's treated as a code point and the converted code point is returned (as a number).

Parameters

string:

The string to uppercase.

Example

print(utf8.title("привет")) -- 'ПРИВЕТ'
print(utf8.title("Привет")) -- 'ПРИВЕТ'

utf8.width

utf8.width(string[, ambi_is_double[, default_width]]): Calculate the widths of the given string. If the string is a code point, return the width of this code point.

Parameters

string:

The input string to work on.

ambi_is_double:

(optional) if provided, the ambiguous width character's width is 2, otherwise it's 1.

default_width:

(optional) if provided, this will be the width of unprintable character, used display a non-character mark for these characters.

utf8.widthindex

utf8.widthindex(string, location[, ambi_is_double[, default_width]]): Returns the character index at the location in the given string as well as the offset and the width. This is a reverse operation of utf8.width().

Parameters

string:

The input string to work on.

location:

location to get the width of.

ambi_is_double:

(optional) if provided, the ambiguous width character's width is 2, otherwise it's 1.

default_width:

(optional) if provided, this will be the width of unprintable character, used display a non-character mark for these characters.

Manual:String Functions

Contents

String Functions

string.byte, utf8.byte

string.char, utf8.char

string.cut

string.dump

string.enclose

string.ends

string.find, utf8.find

string.findPattern

string.format

string.genNocasePattern

string.gfind

string.gmatch, utf8.gmatch

string.gsub, utf8.gsub

string.len, utf8.len

string.lower, utf8.lower

string.match, utf8.match

string.rep

string.reverse, utf8.reverse

string.split

string.starts

string.sub, utf8.sub

string.title

string.trim

string.upper, utf8.upper

utf8.charpos

utf8.escape

utf8.fold

utf8.insert

utf8.ncasecmp

utf8.next

utf8.remove

utf8.title

utf8.width

utf8.widthindex

Navigation menu

Search