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pattern, repl, n) | Returns a copy of `s` in which all (or the first `n`, if given) occurrences of the `pattern` have been replaced by a replacement string specified by `repl`, which can be a string, a table, or a function.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