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

lua pattern-matching alphanumeric non-alphanumeric
unwise guy picture unwise guy · Aug 25, 2012 · Viewed 19.5k times · Source

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

Nicol Bolas picture Nicol Bolas · Aug 25, 2012

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.

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