GSUB doesnt works without spaces - lua

Question

I was trying to make a simple text cryptor, but the script works only if put spaces after every symbol
code:
local text = ""
local tdext = text:gsub("%S+", {["+"] = "a", ["×"] = "b", ["÷"] = "c", ["="] = "d", ["/"] = "e", ["_"] = "f", ["€"] = "g", ["¥"] = "h", ["₩"] = "i", ["!"] = "j", ["#"] = "k", ["#"] = "l", ["$"] = "m", ["%"] = "n", ["^"] = "o", ["&"] = "p", ["*"] = "q", ["("] = "r", [")"] = "s", ["-"] = "t", ["'"] = "u", [":"] = "v", [";"] = "w", [","] = "x", ["?"] = "y", ["."] = "z", [" "] = " "})
print(tdext)
I tried fixing it, but it doesnt do what it should.
If i put in text variable "÷ =" it outputs "b c", but if i am putting "÷=" in variable it will output "÷=".

Answer 1

Let's take a closer look at your substitutions:
local subs = {
["+"] = "a", ["×"] = "b", ["÷"] = "c", ["="] = "d", ["/"] = "e",
["_"] = "f", ["€"] = "g", ["¥"] = "h", ["₩"] = "i", ["!"] = "j",
["#"] = "k", ["#"] = "l", ["$"] = "m", ["%"] = "n", ["^"] = "o",
["&"] = "p", ["*"] = "q", ["("] = "r", [")"] = "s", ["-"] = "t",
["'"] = "u", [":"] = "v", [";"] = "w", [","] = "x", ["?"] = "y",
["."] = "z", [" "] = " "
}
local tdext = text:gsub("%S+", subs)
%S+ matches a sequence of one or more non-space bytes. If you have single characters - multi-byte (UTF-8) or single-byte (ASCII) - this will work fine. However if you have a sequence of multiple characters (say, +-), this won't perform the replacement, since both + and - won't be found in your lookup table. The same is the case for the multi-byte ÷=: ÷ = works, because your characters are separated by spaces; ÷= doesn't, because the pattern greedily matches the sequence.
If this is supposed to be a character-wise substitution, you'll need to match characters (UTF-8 sequences, which includes ASCII). Lua 5.3 and later will have the "constant" utf8.charpattern which is a pattern string matching a single UTF-8 character. If you have a recent Lua version, the fix becomes trivial: Just replace "%S+" with utf8.charpattern:
local tdext = text:gsub(utf8.charpattern, subs)
In older Lua versions (up to and including 5.2), you'll have to write this pattern yourself, using decimal escapes:
local charpattern = "[%z-\127\194-\244][\128-\191]*"
local tdext = text:gsub(charpattern, subs)
Alternatively, if you also want to support multi-character substitutions, you can simply apply the substitutions one by one (which is however significantly less efficient by a factor linear in the number of entries in the subs table):
-- We need to escape everything to make Lua treat it as a literal string
local function escape_pattern(str)
return str:gsub(".", "%%.")
end
local tdext = text
for from, to in pairs(subs) do
tdext = tdext:gsub(escape_pattern(from), escape_pattern(to))
end