lua: string splitting by character position

splitStringByCharPos.lua

print(string.sub("123456789", 1))        --should print original string
print(string.sub("123456789", 1, -1))    --should print original string
print(string.sub("123456789", 4, 7))     --should print 4567
print(string.sub("123456789", 1, 4))     --should print the 1st 4 chars
print(string.sub("123456789", -4, -1))   --should print the last 4 chars
print(string.sub("123456789", 2, -2))    --should remove the first and last char
print(string.sub("123456789", 2))        --should remove the first char
print(string.sub("123456789", 1, -2))    --should remove the last char
print(string.sub("123456789", -2))       --should print only the last 2 chars
print(string.sub("123456789", 1, 2))     --should print only the first 2 chars