 # Lua

## Overview

### For Loops Overviewtop ↑

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 = 3
--  arr = 2
--  arr = 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
``````

### Conditionals Overviewtop ↑

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
``````

## Language

### ipairs( table )top ↑

#### Syntax

```for i,v in ipairs( t ) do body end

-- This will iterate over the pairs:
--   (1,t), (2,t), ...
```

`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.

 table table to iterate over

#### Returns

Returns three values: an iterator function, the table, and 0

### pairs( table )top ↑

#### Syntax

```for k,v in pairs( t ) do body end

-- This will iterate over all key-value
-- pairs in table t
```

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

 table table to iterate over

#### Returns

Returns three values: the next function, the table t, and nil

## Tables

### table.concat( table, sep )top ↑

#### Syntax

```table.concat( table )
table.concat( table, sep )
table.concat( table, sep, i )
table.concat( table, sep, i, j )
```

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.

 table table to concatenate sep separator string i int, starting index to concatenate from j int, ending index

#### Returns

A string of the elements in `table` concatenated with each other, separated by `sep`

### table.move( a1, f, e, t, a2 )top ↑

#### Syntax

```table.move( a1, f, e, t )
table.move( a1, f, e, t, a2 )
```

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.

 a1 table to move elements from f integer, starting index in table to move from e integer, ending index in table to move from t integer, starting index in table to move into a2 table to move elements into (defaults to `a1`)

### table.insert( table, pos, value )top ↑

#### Syntax

```table.insert( table, value )
table.insert( table, pos, value )
```

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.

 table table to insert into pos int, position to inset value value to insert

### table.remove( table, pos )top ↑

#### Syntax

```table.remove( table )
table.remove( table, pos )
```

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.

 table table to insert into pos int, position of value to remove

#### Returns

Value of the removed element

### table.pack(...)top ↑

#### Syntax

```table.pack( ... )
```

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.

 ... arguments to pack into table

#### Returns

table with all parameters packed

### table.unpack(list)top ↑

#### Syntax

```table.unpack( list )
```

Returns the elements from the given list.

 list list to unpack

#### Returns

elements unpacked from list

### table.sort( table )top ↑

#### Syntax

```table.sort( table )
table.sort( table, comp )
```

Sorts table elements in a given order, in-place, from `table` 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.

 table the table to sort comp a function that receives two table elements and returns true when the first is less than the second

## Strings

### string.byte( s, i, j )top ↑

#### Syntax

```string.byte( s )
string.byte( s, i )
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`. These indices are corrected following the same rules of `string.sub`.

 s string to use i first index, defaults to 1 j last index, defaults to `i`

#### Returns

The internal numerical codes for characters s[i] up to s[j]

### string.char( ... )top ↑

#### Syntax

```string.char( ... )
```

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.

 ... a variable number of numerical codes

#### Returns

String composed of characters equal to the numerical codes used as arguments

### string.dump( function )top ↑

#### Syntax

```string.dump( function )
string.dump( function, strip )
```

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).

 function a function to convert to binary string strip boolean, whether to strip debug information

#### Returns

Binary string representation of the specified function

### string.find( s, pattern )top ↑

#### Syntax

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

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.

 s string to search in pattern pattern to look for init starting character in string to search from, default is 1 plain boolean, perform a plain substring search

#### Returns

The start and end indices of the match, or `nil` if no match. If the pattern has captures then captured values are also returned after the indices

### string.format( formatstring, ... )top ↑

#### Syntax

`string.format( formatstring, ... )`

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.

 formatstring string defining the format

#### Examples

s = string.format("Number is %d", 5) print( s ) -- prints "Number is 5"

#### Returns

A formatted string

### string.len( s )top ↑

#### Syntax

`string.len( s )`

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

 s get the length of this string

#### Returns

Length of string `s`

### string.gmatch( s, pattern )top ↑

#### Syntax

```string.gmatch( s, pattern )
```

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.

 s string to search pattern pattern to match

#### Examples

-- Print each word in string s = "hello world from Lua" for w in string.gmatch(s,"%a+") do print(w) end
-- Generate table from string t = {} s = "from=world, to=Lua" for k, v in string.gmatch(s,"(%w+)=(%w+)") do t[k] = v end

#### Returns

Iterator function over matches of `pattern` within the string

### string.gsub( s, pattern, repl )top ↑

#### Syntax

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

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).

 s string to substitute pattern pattern to match repl string, table or function, replacement parameter n integer, number of occurrences to match (all if not specified)

#### Examples

x = string.gsub("hello world", "(%w+)", "%1 %1")

#### Returns

Returns a copy of `s` with substitutions made, as well as the number of matches

### string.lower( s )top ↑

#### Syntax

`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.

 s get a lowercase version of this string

#### Returns

Lowercase version of string `s`

### string.upper( s )top ↑

#### Syntax

`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.

 s get an uppercase version of this string

#### Returns

Uppercase version of string `s`

### string.match( s, pattern )top ↑

#### Syntax

```string.match( s, pattern )
string.match( s, pattern, init )
```

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.

 s string to search pattern pattern to match init starting location in string

#### Returns

Captures from the first match of `pattern` in string `s`, or `nil` if none were found

### string.rep( s, n )top ↑

#### Syntax

`string.rep( s, n )`

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

 s string to replicate n int, number of times to replicate the string

#### Returns

`n` concatenations of string `s`

### string.reverse( s )top ↑

#### Syntax

`string.reverse( s )`

This function returns the string `s` reversed.

 s string to reverse

#### Returns

`s` reversed

### string.sub( s, i, j )top ↑

#### Syntax

```string.sub( s, i )
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`.

 s find substring of this string i int, starting index j int, ending index

#### Returns

Substring of string `s`

### string.pack( fmt, v1, v2, ... )top ↑

#### Syntax

```string.pack( fmt, v1, v2, ... )
```

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

 fmt format string specifying binary format ... arguments to pack

#### Returns

Values packed into binary string

### string.packsize( fmt )top ↑

#### Syntax

```string.packsize( 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'

 fmt format string specifying binary format

#### Returns

Size of string packed with the given format

### string.unpack( fmt, s )top ↑

#### Syntax

```string.unpack( fmt, s )
string.unpack( fmt, s, pos )
```

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`.

 fmt format string specifying binary format s string to unpack

#### Returns

The values packed in `s`

### Patterns Overviewtop ↑

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: (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
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.

## Math

### math.abs( value )top ↑

#### Syntax

`math.abs( value )`

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

 value int or float, the number to get the absolute value of

#### Returns

The absolute value of value

### math.acos( value )top ↑

#### Syntax

`math.acos( value )`

This function returns the arc cosine of `value` in radians

 value float, compute the arc cosine of this number

#### Returns

The arc cosine of value in radians

### math.asin( value )top ↑

#### Syntax

`math.asin( value )`

This function returns the arc sine of `value` in radians

 value float, compute the arc sine of this number

#### Returns

The arc sine of value in radians

### math.atan( y, x )top ↑

#### Syntax

```math.atan( y )
math.atan( y, x )
```

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.

 y float, y value x float, x value optional, defaults to 1

#### Returns

The arc tangent of value in radians

### math.ceil( value )top ↑

#### Syntax

`math.ceil( value )`

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.

 value int or float, compute the smallest integer larger than or equal to this number

#### Returns

The smallest integer larger than or equal to value

### math.cos( value )top ↑

#### Syntax

`math.cos( value )`

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

 value int or float, compute the cosine of this number

Cosine of value

### math.cosh( value )top ↑

#### Syntax

`math.cosh( value )`

This function returns hyperbolic cosine of `value`.

 value int or float, compute the hyperbolic cosine of this number

#### Returns

Hyperbolic cosine of value

### math.deg( value )top ↑

#### Syntax

`math.deg( value )`

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

 value int or float, angle in radians to convert to degrees

#### Returns

Angle specified by value (in radians) in degrees

#### Syntax

`math.rad( value )`

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

 value int or float, angle in degrees to convert to radians

#### Returns

Angle specified by value (in degrees) in radians

### math.exp( value )top ↑

#### Syntax

`math.exp( value )`

This function returns e raised to `value`

 value int or float, exponent of e

#### Returns

e raised to the power of value

### math.floor( value )top ↑

#### Syntax

`math.floor( 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.

 value int or float, compute the largest integer smaller than or equal to this number

#### Returns

The largest integer smaller than or equal to value

### math.fmod( x, y )top ↑

#### Syntax

`math.fmod( x, y )`

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

 x int or float y int or float

#### Returns

The remainder of the division of x by y

### math.frexp( value )top ↑

#### Syntax

`math.frexp( value )`

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).

 value int or float

#### 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).

### math.ldexp( m, e )top ↑

#### Syntax

`math.ldexp( m, e )`

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

 m int or float e int

m2^e

### math.log( x, base )top ↑

#### Syntax

```math.log( x )
math.log( x, base )
```

This function returns the logarithm of `x` given `base`. The default value for `base` is e so that the function returns the natural logarithm of `x`.

 x int or float, compute the logarithm of this value base int or float, base of the logarithm, defaults to e if not specified

#### Returns

The logarithm of `x` given `base`

### math.max( value, ... )top ↑

#### Syntax

`math.max( value, ... )`

This function returns maximum value among its arguments.

 value any comparable value

#### Returns

The maximum value among its arguments

### math.min( value, ... )top ↑

#### Syntax

`math.min( value, ... )`

This function returns minimum value among its arguments.

 value any comparable value

#### Returns

The minimum value among its arguments

### math.modf( value )top ↑

#### Syntax

`math.modf( value )`

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

 value int or float

#### Returns

Two numbers, the integral part of value and the fractional part of value

### math.pow( x, y )top ↑

#### Syntax

`math.pow( x, y )`

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

 x int or float y int or float

x raised to y

### math.random()top ↑

#### Syntax

```math.random()
math.random( maximum )
math.random( minimum, maximum )
```

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].

 minimum int, minimum value of returned pseudo-random number maximum int, maximum value of returned pseudo-random number

#### Returns

A uniform pseudo-random real number or integer (depending on parameters)

### math.randomseed( value )top ↑

#### Syntax

`math.randomseed( value )`

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

 value int, seed of the pseudo-random number generator

#### Returns

A uniform pseudo-random real number or integer (depending on parameters)

### math.sin( value )top ↑

#### Syntax

`math.sin( value )`

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

 value int or float, compute the sine of this number

Sine of value

### math.sinh( value )top ↑

#### Syntax

`math.sinh( value )`

This function returns hyperbolic sine of `value`.

 value int or float, compute the hyperbolic sine of this number

#### Returns

Hyperbolic sine of value

### math.tan( value )top ↑

#### Syntax

`math.tan( value )`

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

 value int or float, compute the tangent of this number

Tangent of value

### math.tanh( value )top ↑

#### Syntax

`math.tanh( value )`

This function returns hyperbolic tangent of `value`.

 value int or float, compute the hyperbolic tangent of this number

#### Returns

Hyperbolic tangent of value

### math.sqrt( value )top ↑

#### Syntax

`math.sqrt( value )`

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

 value int or float, compute the square root of this number

#### Returns

Square root of value

### math.tointeger( value )top ↑

#### Syntax

`math.tointeger( value )`

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

 value float, value to convert to integer

#### Returns

`value` converted to an integer, or nil

### math.type( value )top ↑

#### Syntax

`math.type( value )`

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

 value int or float, get the type of this value

#### Returns

"integer" or "float"

### math.ult( m, n )top ↑

#### Syntax

`math.ult( m, n )`

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

 m integer, value for m n integer, value for n

#### Returns

true if `m` is below integer `n` when compared as unsigned

### math.hugetop ↑

#### Syntax

`math.huge`

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

#### Returns

A value larger than or equal to any other numerical value

### math.pitop ↑

#### Syntax

`math.pi`

The value of pi.

Value of pi

### math.maxintegertop ↑

#### Syntax

`math.maxinteger`

Specifies an integer with the maximum value for an integer

#### Returns

Maximum value for an integer

### math.minintegertop ↑

#### Syntax

`math.mininteger`

Specifies an integer with the minimum value for an integer

#### Returns

Minimum value for an integer

## Date and Time

### os.clock()top ↑

#### Syntax

`os.clock()`

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

#### Returns

Approximation of the amount in seconds of CPU time used by the program.

### os.difftime( t2, t1 )top ↑

#### Syntax

`os.difftime( t2, t1 )`

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

 t2 Ending time t1 Starting time

#### Returns

Number of seconds from time `t1` to time `t2`.

### os.date( format )top ↑

#### Syntax

```os.date()
os.date( format )
os.date( format, time )
```

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')`).

 format String used to format the returned date time If the time argument is present, this is the time to be formatted (see the os.time function for a description of this value).

#### Returns

A string or a table containing the date and time.

### os.setlocale( locale )top ↑

#### Syntax

```os.setlocale( locale )
os.setlocale( locale, category )
```

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.

 locale String specifying a locale, can be nil or the empty string. category String specifying a category to set, can be "all", "collate", "ctype", "monetary", "numeric", or "time"

#### Returns

When called with `nil` for the first argument, returns the name of the current locale for the given category.

### os.time()top ↑

#### Syntax

```os.time()
os.time( table )
```

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`.

 table This table must have fields `year`, `month`, and `day`, and may have fields `hour`, `min`, `sec`, and `isdst`

#### Returns

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`.