From the official Lua Reference (http://www.lua.org):
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 metatable itself. Therefore, you can use the string functions in object-oriented style. For instance, string.byte(s, i) can be written as s:byte(i).
A character class is used to represent a set of characters. The following combinations are allowed in describing a character class:
The interaction between ranges and classes is not defined. Therefore, patterns like [%a-z] or [a-%%] have no meaning.
The definitions of letter, space, and other character groups depend on the current locale. In particular, the class [a-z] may not be equivalent to %l.
A pattern item may be
A pattern is a sequence of pattern items. A `^´ at the beginning of a pattern anchors the match at the beginning of the subject string. A `$´ at the end of a pattern anchors the match at the end of the subject string. At other positions, `^´ and `$´ have no special meaning and represent themselves.
A pattern may contain sub-patterns enclosed in parentheses; they describe captures. When a match succeeds, the substrings of the subject string that match captures are stored (captured) for future use. Captures are numbered according to their left parentheses. For instance, in the pattern "(a*(.)%w(%s*))", the part of the string matching "a*(.)%w(%s*)" is stored as the first capture (and therefore has number 1); the character matching "." is captured with number 2, and the part matching "%s*" has number 3.
As a special case, the empty capture () captures the current string position (a number). For instance, if we apply the pattern "()aa()" on the string "flaaap", there will be two captures: 3 and 5.
A pattern cannot contain embedded zeros. Use %z instead.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.Receives 0 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.
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.
Any debug information is stripped out here.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 may 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.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.
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 loops = "hello world from Lua" for w in string.gmatch(s, "%a+") do print(w) endwill 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
Returns a copy of s in which all occurrences of the pattern have been replaced by a replacement string specified by repl, which may be a string, a table, or a function. gsub also returns, as its second value, the total number of substitutions made.
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).
The optional last parameter n limits the maximum number of substitutions to occur. For instance, when n is 1 only the first occurrence of pattern is replaced.
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"