String

< Scripting | Data Types

Strings are sequences of letters, numbers, and symbols.

Making a string

The most common method of creating strings is to put double quotes around the characters you want. See the code below for an example:

local str = "Hello, world!"

This will cause str to contain the string Hello, world. However, what if you wanted to have double quotes within your string? If you have double quotes in a string, it will cause unwanted effects.

local str = "Hello, "Dave"!" -- We don't want this!

How can we fix this? There are other ways to create a string. We can use single quotes, or we can use double brackets.

local str0="Hello, world!"
local str1='Hello, "world"!'
local str2=[[Hello, "world"!]] 

print(str0)
print(str1)
print(str2)

Hello, world! Hello, "world"!

Hello, "world"!

Combining strings

Let's say you wanted to combine two strings into one. This can be easily done by using ( .. ) in between the two strings.

local str0="Hello,"
local str1=" world!"
local str2=str0 .. str1
print(str0)
print(str1)
print(str2)

Hello,

world!

Hello, world!

The process of combining two strings into one is known as concatenation

Converting a string to a number

You can easily convert a string to a number by using the tonumber() function. This function takes one argument, which is a string, and will return the string into a number. The string must be a sequence of characters that resembles a number, such as "5128", "2", etc. Any strings that don't resemble numbers, such as "Hello", will return nil.

This is an example of tonumber() usage.

a = "123"
b = 5 + tonumber(a) --tonumber() usage here

print(b) --128

Math and strings

An important note with strings is that if you try to perform arithmetic on a string value, it will try to convert the string to a number. If your value can't be converted to a number, you will get an error.

print("5" + 1)
print ("whoops"+1)

6

Cmd:1: attempt to perform arithmetic on a string value

In the first example, "5" was converted from a string to a number (notice "5" was in quotes, but 1 was not.) In the second example "whoops" could not be converted to a number, because it was a word.

print("50" == 50)           -- false, because a string is not equal to a number.
print(tostring(50) == "50") -- true, because you converted the number 50 to a string
print(tonumber("50") == 50) -- true, because you converted the string "50" to a number
print(50 .. "" == "50")     -- true, because you tacked on an empty string to the end of the number 50, converting 50 to a string.

Advanced

This will also work with hexadecimal numbers:

print(0xf == 15) -- true, because 0xf is a hexadecimal number which equals 15
print(tonumber("0xf") == 15)   -- true, because you converted the string "0xf" to a number, 0xf

as well as with other based numbers, but you have to specify the base:

print(tonumber("00001111",2)) -- prints 15
print(tonumber("00001111",2)==15) -- prints true

print(tonumber("774",8)) -- prints 508
print(tonumber("774",8)==508) -- prints true

Literals

print("hello")
print('hello')
print([[hello]])

Will all result in: hello

This allows you to nest a string within another string:

print('hello "Lua user"')
print("Its [[content]] hasn't got a substring.")
print([[Let's have more "strings" please.]])

hello "Lua user" Its content hasn't got a substring.

Let's have more "strings" please.

Multiline literals

print([[Multiple lines of text
can be enclosed in double square
brackets.]])

Multiple lines of text

can be enclosed in double square

brackets.

You can also use normal quotation marks with a backslash at the end of each line to create multiline strings:

local str = "line1\
line2\
line3"
print(str)

line1 line2

line3

Nesting square brackets

Nested brackets rely on the use of equals signs to distinguish one nested bracket from another.

Example:

print([==[
one [=[two]=] one
]=])
print([===[
one [=[two]=] one
]===])

one [=[two]=] one

one [=[two]=] one

Escaping

In single or double quotes, but not block quotes, you can use backslashes (\) to embed any character.

Backslash followed by certain letters have special meanings (see the Lua Manual).

A backslash followed by punctuation or newline overrides any special meaning and puts the character in the string. This is most useful in put quotes or backslash into a quoted string.

print( 'String \'abc\'' )
print( "String with \" \\ and \' " )

A backslash followed by 1-3 numbers represents the string.byte value of that number.

print( "\104\105" )

hi

Be careful if you use fewer than 3 numbers ("\0" for example) and a number comes after it.

print( "\000123" ~= "\0123" )

See also

• Programming in Lua 2.4 -- Strings
• Lua 5.1 Reference Manual
• StringsTutorial
• StringValue