Module string String Manipulation.
This library provides generic functions for string manipulation, such as finding and extracting substrings, and pattern matching. When indexing a string in Lua, the first character is at position 1 (not at 0, as in C). Indices are allowed to be negative and are interpreted as indexing backwards, from the end of the string. Thus, the last character is at position -1, and so on.

The string library provides all its functions inside the table string. It also sets a metatable for strings where the __index field points to the string table. Therefore, you can use the string functions in object-oriented style. For instance, string.byte(s, i) can be written as s:byte(i).

The string library assumes one-byte character encodings.

Type string

string.byte(s, i, j) Returns the internal numerical codes of the characters s[i], s[i+1], ..., s[j].
string.char() Receives zero or more integers.
string.dump() Returns a string containing a binary representation of the given function, so that a later loadstring on this string returns a copy of the function.
string.find(s, pattern, init, plain) Looks for the first match of pattern in the string s.
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).
string.gmatch(s, pattern) Returns an iterator function that, each time it is called, returns the next captures from pattern over string s.
string.gsub(s, pattern, repl, n) Returns a copy of s in which all (or the first n, if given) occurrences of the pattern have been replaced by a replacement string specified by repl, which can be a string, a table, or a function.
string.len(s) Receives a string and returns its length.
string.lower(s) Receives a string and returns a copy of this string with all uppercase letters changed to lowercase.
string.match(s, pattern, init) Looks for the first match of pattern in the string s.
string.rep(s, n) Returns a string that is the concatenation of n copies of the string s.
string.reverse(s) Returns a string that is the string s reversed.
string.sub(s, i, j) Returns the substring of s that starts at i and continues until j; i and j can be negative.
string.upper(s) Receives a string and returns a copy of this string with all lowercase letters changed to uppercase.

Type string

Field(s)

string.byte(s, 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.

Parameters

string.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.dump()

Returns a string containing a binary representation of the given function, so that a later loadstring on this string returns a copy of the function.
function must be a Lua function without upvalues.

string.find(s, pattern, init, plain)

Looks for the first match of pattern in the string s.
If it finds a match, then find returns the indices of s 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.

Parameters

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.
		
Parameter

		


		



string.gmatch(s, pattern)



	 Returns an iterator function that, each time it is called, returns the
 next captures from pattern over string s.
	
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.
		
Parameters

		


		



string.gsub(s, pattern, repl, n)



	 Returns a copy of s 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).



 Here are some examples:


 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"



		
Parameters

		


		



string.len(s)



	 Receives a string and returns its length.
	
The empty string "" has
 length 0. Embedded zeros are counted, so "a\000bc\000" has length 5.
		
Parameter

		


		



string.lower(s)



	 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.
		
Parameter

		


		



string.match(s, pattern, init)



	 Looks for the first match of pattern in the string s.
	
If it
 finds one, then match returns the captures from the pattern; otherwise
 it returns nil. If pattern specifies no captures, then the whole match
 is returned. A third, optional numerical argument init specifies where
 to start the search; its default value is 1 and can be negative.
		
Parameters

		


		



string.rep(s, n)



	 Returns a string that is the concatenation of n copies of the string
 s.
	



		
Parameters

		


		



string.reverse(s)



	 Returns a string that is the string s reversed.
	



		
Parameter

		


		



string.sub(s, i, j)



	 Returns the substring of s that starts at i and continues until
 j; i and j can be negative.
	
If j is absent, then it is assumed to
 be equal to -1 (which is the same as the string length). In particular,
 the call string.sub(s,1,j) returns a prefix of s with length j, and
 string.sub(s, -i) returns a suffix of s with length i.
		
Parameters

		


		



string.upper(s)



	 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.
		
Parameter