Lua: How to check if a string contains only numbers and letters?

Question

Simple question may have a simple answer, but my current solution seems horrible.

local list = {'?', '!', '@', ... etc)
for i=1, #list do 
    if string.match(string, strf("%%%s+", list[i])) then
         -- string contains characters that are not alphanumeric.
    end
 end

Is there a better way to do this.. maybe with string.gsub?

Thanks in advance.

Answer 1

If you're looking to see if a string contains only alphanumeric characters, then just match the string against all non-alphanumeric characters:

if(str:match("%W")) then
  --Improper characters detected.
end

The pattern %w matches alphanumeric characters. By convention, a pattern than is upper-case rather than lowercase matches the inverse set of characters. So %W matches all non-alphanumeric characters.

Answer 2

You can create a set match with []

local patt = "[?!@]"

if string.match ( mystr , patt ) then
    ....
end

Note that character classes in lua only work for single characters (not words). There are built in classes, %W matches non-alphanumerics, so go ahead and use that as a shortcut.

You can also add the inbuilt classes to your set:

local patt = "[%Wxyz]"

Will match all non-alphanumerics AND characters x, y or z

Answer 3

I use this Lua two-liner:

  local function envIsAlphaNum(sIn)
    return (string.match(sIn,"[^%w]") == nil) end

When it detects a non-alphanumeric it returns false