lua string.upper not working with accented characters?

Question

I'm trying to convert some French text to upper case in lua, it is not converting the accented characters. Any idea why?

test script:

print('échelle')
print(string.upper('échelle'))
print('ÉCHELLE')
print(string.lower('ÉCHELLE'))

output:

échelle
éCHELLE
ÉCHELLE
Échelle

Answer 1

It might be a bit overkill, but you can do this with slnunicode (which is available in LuaRocks).

require "unicode"
print(unicode.utf8.upper("échelle"))
-- ÉCHELLE

You may need to use unicode.ascii.upper or unicode.latin1.upper depending on the encoding of your source files.