Given a string s in Lua:
s = "abc123" If the string is non-empty, I want to store the first character of this string in a variable s1, else store nothing.
I've tried the following, but both return nil:
s1 = s[1] s1 = s[0] How can I get the first character without using external Lua libraries?
You can use string.sub() to get a substring of length 1:
> s = "abc123" > string.sub(s, 1, 1) a This also works for empty strings:
> string.sub("", 1, 1) -- => "" 
You can also use this shorter variant:
s:sub(1, 1) 
local string_meta = getmetatable('') function string_meta:__index( key ) local val = string[ key ] if ( val ) then return val elseif ( tonumber( key ) ) then return self:sub( key, key ) else error( "attempt to index a string value with bad key ('" .. tostring( key ) .. "' is not part of the string library)", 2 ) end end local str = "Hello" print(str[1]) 
s[1], but how to get the first character. Also, could you add a bit more explanation on how the sample works, how to use it, and what the expected output should be (matching the original example)?i saw the code of @x0r and i want to clarify what he did :
https://www.lua.org/manual/5.1/manual.html says in 2.8 – Metatables :
A metatable controls how an object behaves in arithmetic operations, order comparisons, concatenation, length operation, and indexing.
Values of all other types share one single metatable per type; that is, there is one single metatable for all numbers, one for all strings, etc.
so we can create an index metamethod for the string type and all variable of string type well have this new behaviour
to know more about the index metamethod check Programming in Lua Chapter 13. Metatables and Metamethods
I made 3 functions for strings.
Also, yes, I know this post is a year old, and that it was already answered, but I still made a function for you.
(And I already know that uppercase and lowercase methods exist but I don't care.)
function toUppercase(originalString, printString) if printString ~= true and printString ~= false then printString = false end if printString == true then print(originalString:upper()) else return originalString:upper() end end function toLowercase(originalString, printString) if printString ~= true and printString ~= false then printString = false end if printString == true then print(originalString:lower()) else return originalString:lower() end end function toTitleCase(originalString, printString) if printString ~= true and printString ~= false then printString = false end changeString = originalString:gsub("%W%l", string.upper):sub(0) titleCase = changeString:sub(1, 1):upper() .. changeString:sub(2, #changeString) if printString == true then print(titleCase) else return titleCase end end 
s="ö" ; s:byte(1) == 195 ; s:byte(2) == 164string.sub()also doesn't work for unicode :-)s1 = s:match"^.?[\128-\191]*"s[1]returnnilwithout error?sis a string, not a table.