String

Up one category:
Properties

Introduction

Strings are sequences of characters, letters, numbers, letters AND numbers, symbols, and so forth.

A script of

x = "Hi mom"
y = "123456"
z = "Bob12345"
n = "abc!@#$%^&*()123456789"

print (x)
print (y)
print (z)
print (n)

will print in the output bar Hi mom, 123456, Bob12345, and abc!@#$%^&*()123456789 . Strings differ from Numbers in that you can't allocate a name like "Bob" to numbers.

Another 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.

Example:

print ("5"+1)
6
print ("whoops"+1)
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.

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)

Output:
128

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

Quotes

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

Will all result in: hello [1]

This will allow 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.]])

Will result in:

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

Multiline quotes

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

Will result in: Multiple lines of text can be enclosed in double square brackets.

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

local str = "line1\
line2\
line3";

print(str);

Will result in:
line1
line2
line3

Nesting quotes

Nested quotes rely on the use of equals signs to distinguish one nested quote from another.:

Example:

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

Both result in:
one [[two]] one

Escaping

In single or double quotes, but not block quotes. You can use escapes to embed any character.

A backslash(\) followed by certain letters has special meaning (see 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 less than 3 numbers ("\0" for example) and a number comes after it.

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

If you want to escape any of the following characters (", ', or /,) you can use the %q character class along with the string.format string function. Here's an example:

string.format(string, "%q")

See Also

Programming in Lua 2.4 -- Strings

Lua 5.1 Reference Manual

StringsTutorial

StringValue