Lua

You can use for loops in Lua to iterate over arrays and tables, performing tasks for each element.

This example simply iterates i over the values 1 to 10

-- Iterate from 1 to 10
for i = 1, 10 do
    print( i )
end

This example uses the ipairs function to sequentially iterate over a table. Note that ipairs only works on tables that have sequential elements beginning at 1.

-- Iterate over an array named 'arr'
arr = { 3, 2, 1 }

for i,v in ipairs(arr) do
    print( "arr["..i.."] = "..v )
end

-- Prints:
--  arr[1] = 3
--  arr[2] = 2
--  arr[3] = 1

This example uses pairs to iterate over all the key/value pairs in a table, unlike ipairs the keys do not have to be integral values, and can be anything.

-- Iterate over a table named 'tab'
tab = { x = 3, y = "string", z = 1 }

for key,value in pairs(tab) do
    print( "tab."..key.." = "..value )
end

-- Prints:
--  tab.y = string
--  tab.x = 3
--  tab.z = 1

Use conditionals to test for a particular circumstance and then branch your code appropriately. See the examples below.

-- Check if x is equal to 10
if x == 10 then
    print( "x equals 10" )
end

-- else and elseif
if x == 10 then
    print( "x is 10" )
elseif x == 5 then
    print( "x is 5" )
else    
    print( "x is something else: "..x )
end

-- Checking multiple values
if x == 10 and y < 5 then
    print( "x is 10 and y is less than 5" )
elseif x == 5 or y == 3 then
    print( "x is 5 or y is 3" )
else
    print( "x is "..x.." and y is "..y )
end

Use while and repeat loops to repeat code until a condition is true. While loops are used when you can't predict the number of times a loop will iterate, such as when reading input from a file or testing for a key press.

-- simple while loop. The condition is evaluated at the beginning of the loop. The loop will never get executed if the condition is false at the beginning of the loop.
while i<=5 do
    print(i)
    i=i+1
end

-- repeat loop. The condition is evaluated at the end of the loop, so the code always gets executed at least once
repeat
    print(i)
    i=i+1
until i>5

-- break statement: break exits a loop and continues program flow with the statement immediately following the end or until condition
while true do
    print(i)
    i=i+1
    if i>5 then 
        break 
    end
end

ipairs can be used to iterate over a table sequentially, starting from the index 1 and continuing until the first integer key absent from the table. Returns three values: an iterator function, the table, and 0.

pairs can be used to iterate over a tables key-value pairs. Returns three values: the next function, the table t, and nil.

Given an array where all elements are strings or numbers, returns table[i]..sep..table[i+1] ... sep..table[j]. The default value for sep is the empty string, the default for i is 1, and the default for j is the length of the table. If i is greater than j, returns the empty string.

Moves elements from table a1 into table a2. This function performs the equivalent to the multiple assignment: a2[t], ... = a1[f], ..., a1[e]. The default value for a2 is a1. The destination range can overlap with the source range. Index f must be positive.

Inserts element value at position pos in table, shifting up other elements to open space, if necessary. The default value for pos is n+1, where n is the length of the table, so that a call table.insert(t,x) inserts x at the end of table t.

Removes from table the element at position pos, shifting down other elements to close the space, if necessary. Returns the value of the removed element. The default value for pos is n, where n is the length of the table, so that a call table.remove(t) removes the last element of table t.

Returns a new table with all parameters stored into keys 1, 2, etc. and with a field "n" with the total number of parameters. Note that the resulting table may not be a sequence.

Returns the elements from the given list.

Sorts table elements in a given order, in-place, from table[1] to table[n], where n is the length of the table. If comp is given, then it must be a function that receives two table elements and returns true when the first is less than the second (so that not comp(a[i+1],a[i]) will be true after the sort). If comp is not given, then the standard Lua operator < is used instead.

The sort algorithm is not stable; that is, elements considered equal by the given order may have their relative positions changed by the sort.

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. These indices are corrected following the same rules of string.sub.

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.

Returns a string containing a binary representation (a binary chunk) of the given function, so that a later load on this string returns a copy of the function (with new upvalues). If strip is a true value, the binary representation is created without debug information about the function (local variable names, lines, etc).

Looks for the first match of pattern in the string s. If it finds a match, then string.find() returns the indices of s where the 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 the fourth optional argument plain turns off the pattern matching facilities so the function performs 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 arguments following the description given in the first argument, which must be a string. The format string follows the same rules as the printf family of standard C functions. The only difference are that the options/modifiers *, 1, 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, for example all double quotes, newlines, embedded zeros and backslashes will be escaped when written.

Receives a string and returns its length. The empty string "" has length 0.

Returns an iterator function that, each time it is called, returns the next captures from pattern (see Patterns Overview) over the string s. If pattern specifies no captures, then the whole match is produced in each call.

Returns a copy of s in which all (or the first n, if given) occurrences of the pattern (see Patterns Overview) 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. The name gsub comes from Global SUBstitution.

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 %d, with d between 1 and 9, stands for the value of the d-th captured substring. 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 repl is a function, then this function is called every time a match occurs, with all captured substrings passed as arguments, in order.

In any case, if the pattern specifies no captures, then it behaves as if the whole pattern was inside a capture.

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).

Receives a string and returns a copy of this string with all uppercase letters changed to lowercase. All other characters are left unchanged.

Receives a string and returns a copy of this string with all lowercase letters changed to uppercase. All other characters are left unchanged.

Looks for the first match of pattern in the string s. If it finds one then string.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 is 1 and can be negative.

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

This function returns the string s reversed.

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.

Returns a binary string containing the values v1, v2, etc. packed (that is, serialized in binary form) according to the format string fmt.

Returns the size of a string resulting from string.pack with the given format. The format string cannot have the variable-length options 's' or 'z'

Returns the values packed in string s according to the format string fmt. An optional pos marks where to start reading in s (default is 1). After the read values, this function also returns the index of the first unread byte in s.

Patterns in Lua are described by regular strings, which are interpreted as patterns by the pattern-matching functions string.find, string.gmatch, string.gsub, and string.match. This section describes the syntax and the meaning (that is, what they match) of these strings.

Character Class

A character class is used to represent a set of characters. The following combinations are allowed in describing a character class:

x: (where x is not one of the magic characters
   ^$()%.[]*+-?) represents the character x
   itself.
.: (a dot) represents all characters.
%a: represents all letters.
%c: represents all control characters.
%d: represents all digits.
%g: represents all printable characters except space.
%l: represents all lowercase letters.
%p: represents all punctuation characters.
%s: represents all space characters.
%u: represents all uppercase letters.
%w: represents all alphanumeric characters.
%x: represents all hexadecimal digits.
%x: (where x is any non-alphanumeric character)
    represents the character x.
    This is the standard way to escape
    the magic characters. Any non-alphanumeric
    character (including all punctuations, even
    the non-magical) can be preceded by a '%'
    when used to represent itself in a pattern.
[set]: represents the class which is
    the union of all characters in set.
    A range of characters can be specified
    by separating the end characters of the
    range, in ascending order, with a '-'.
    All classes %x described above can
    also be used as components in set.
    All other characters in set represent
    themselves. For example, [%w_] (or [_%w])
    represents all alphanumeric characters
    plus the underscore, [0-7] represents
    the octal digits, and [0-7%l%-] represents
    the octal digits plus the lowercase letters
    plus the '-' character.
[^set]: represents the complement of set,
    where set is interpreted as above.

For all classes represented by single letters (%a, %c, etc.), the corresponding uppercase letter represents the complement of the class. For instance, %S represents all non-space characters.

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.

Pattern Item

A pattern item can be:

- a single character class, which matches
  any single character in the class;
- a single character class followed by '*',
  which matches zero or more repetitions
  of characters in the class. These
  repetition items will always match
  the longest possible sequence;
- a single character class followed by '+',
  which matches one or more repetitions of
  characters in the class. These repetition
  items will always match the longest
  possible sequence;
- a single character class followed by '-',
  which also matches zero or more repetitions
  of characters in the class. Unlike '*',
  these repetition items will always match
  the shortest possible sequence;
- a single character class followed by '?',
  which matches zero or one occurrence of
  a character in the class. It always
  matches one occurrence if possible;
- %n, for n between 1 and 9; such item
  matches a substring equal to the n-th
  captured string (see below);
- %bxy, where x and y are two distinct
  characters; such item matches strings
  that start with x, end with y,
  and where the x and y are balanced.
  This means that, if one reads the string
  from left to right, counting +1 for an x
  and -1 for a y, the ending y is the first
  y where the count reaches 0.
  For instance, the item %b() matches
  expressions with balanced parentheses.
- %f[set], a frontier pattern; such item
  matches an empty string at any position
  such that the next character belongs to
  set and the previous character does not
  belong to set. The set set is interpreted
  as previously described. The beginning
  and the end of the subject are handled
  as if they were the character '\0'.

Pattern

A pattern is a sequence of pattern items. A caret '^' 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.

Captures

A pattern can 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.

This function returns the absolute value of value. For example, math.abs(-5) returns 5.

This function returns the arc cosine of value in radians

This function returns the arc sine of value in radians

This function returns the arc tangent of value in radians

This function returns the arc tangent of y/x in radians, but uses the sign of both parameters to find the quadrant of the result. It also handles correctly the case of x being zero.

This function returns the smallest integer larger than or equal to value. This rounds a number up to the nearest integer. For example, math.ceil(5.2) returns 6.

This function returns the cosine of value (assumed to be in radians).

This function returns hyperbolic cosine of value.

This function returns the angle specified by value (given in radians) in degrees.

This function returns the angle specified by value (given in degrees) in radians.

This function returns e raised to value

This function returns the largest integer smaller than or equal to value. This rounds a number down to the nearest integer. For example, math.floorTh(5.7) returns 5.

This function returns the remainder of the division of x by y that rounds the quotient towards zero.

This function returns m and e such that value = m2^e, e is an integer and the absolute value of m is in the range [0.5, 1) (or zero when x is zero).

This function returns m2^e (e should be an integer)

This function returns the natural logarithm of value

This function returns the base-10 logarithm of value

This function returns maximum value among its arguments.

This function returns minimum value among its arguments.

This function returns two numbers, the integral part of value and the fractional part of value.

This function returns x raised to y. Equivalent to the expression x^y.

When called without arguments, math.random() returns a uniform pseudo-random real number in the range [0, 1). When called with an integer number maximum, math.random() returns a uniform pseudo-random integer in the range [1, maximum]. When called with two integer numbers, minimum and maximum, math.random() returns a uniform pseudo-random integer in the range [minimum, maximum].

Sets value as the "seed" for the pseudo-random number generator. Equal seeds produce equal sequences of numbers.

This function returns the sine of value (assumed to be in radians).

This function returns hyperbolic sine of value.

This function returns the tangent of value (assumed to be in radians).

This function returns hyperbolic tangent of value.

This function computes the square root of value. You can also use the expression value^0.5 to compute this value.

If value is convertible to an integer, returns that integer. Otherwise returns nil.

This function returns "integer" if value is an integer, "float" if it is a float, or nil if value is not a number.

This function returns a boolean, true if integer m is below integer n when they are compared as unsigned integers.

A value larger than or equal to any other numerical value.

The value of pi.

Specifies an integer with the maximum value for an integer

Specifies an integer with the minimum value for an integer

Returns an approximation of the amount in seconds of CPU time used by the program.

Returns the number of seconds from time t1 to time t2. In POSIX, Windows, and some other systems, this value is exactly t2-t1.

Returns a string or a table containing the date and time, formatted according to the given string format.

If the time argument is present, this is the time to be formatted (see the os.time function for a description of this value). Otherwise, date formats the current time.

If format starts with '!', then the date is formatted in Coordinated Universal Time. After this optional character, if format is the string '*t', then date returns a table with the following fields: year (four digits), month (1--12), day (1--31), hour (0--23), min (0--59), sec (0--61), wday (weekday, Sunday is 1), yday (day of the year), and isdst (daylight saving flag, a boolean).

If format is not '*t', then date returns the date as a string, formatted according to the same rules as the C function strftime.

When called without arguments, date returns a reasonable date and time representation that depends on the host system and on the current locale (that is, os.date() is equivalent to os.date('%c')).

Sets the current locale of the program. locale is a string specifying a locale; category is an optional string describing which category to change: "all", "collate", "ctype", "monetary", "numeric", or "time"; the default category is "all". The function returns the name of the new locale, or nil if the request cannot be honored.

If locale is the empty string, the current locale is set to an implementation-defined native locale. If locale is the string "C", the current locale is set to the standard C locale.

When called with nil as the first argument, this function only returns the name of the current locale for the given category.

Returns the current time when called without arguments, or a time representing the date and time specified by the given table. This table must have fields year, month, and day, and may have fields hour, min, sec, and isdst (for a description of these fields, see the os.date function).

The returned value is a number, whose meaning depends on your system. In POSIX, Windows, and some other systems, this number counts the number of seconds since some given start time (the "epoch"). In other systems, the meaning is not specified, and the number returned by time can be used only as an argument to date and difftime.