myString = "AbAbAb"

-- 转为大写
print(string.upper(myString))

-- 转为小写
print(string.lower(myString))

-- 字符替换
myString = string.gsub("aaaa","a","z",3) -- 字符串，被替换字符，替换字符，替换次数
print(myString)

--
myString = string.find("Hello Lua user", "Hello", 1)
print(myString)