Character Classes Help

[abcxomisgood (Nate)]

So I want to make a textbox that will only allow a single dash (-), and 3 numbers totally in a total maximum of 4 characters. How could I achieve this?
In otherwords I need a number-only textbox that will allow a maximum of 4 characters, one of which needs to be a dash (-)

Currently I have the following script that only allows numbers in the textbox
I have tried looking at the strings post on the documentation but struggled to understand it. Strings | Documentation - Roblox Creator Hub

script.Parent.CallsignFrame.CallsignInput:GetPropertyChangedSignal("Text"):Connect(function()
	script.Parent.CallsignFrame.CallsignInput.Text = script.Parent.CallsignFrame.CallsignInput.Text:gsub("%D+", "")
end)

[legendaryjimmy12]

script.Parent.CallsignFrame.CallsignInput:GetPropertyChangedSignal("Text"):Connect(function()
	local Text = script.Parent.CallsignFrame.CallsignInput.Text
	if Text:len() <= 4 then
		local dash = false
		for i = 1, Text:len() do
			local letter = Text:sub(i,i)
			if letter == "-" and dash == false then
				dash = true
			elseif dash == true then
				break
			elseif not tonumber(letter) then
				break
			end
		end
	end
end)

This should work. you might have to add a system to tell the player that the thing did not go through or you could add something different because this might not fit your needs.

[abcxomisgood (Nate)]

Using your script I came up with this that will limit the characters in the textbox and only allow one dash and numbers as requested.

script.Parent.CallsignFrame.CallsignInput:GetPropertyChangedSignal("Text"):Connect(function()
	local Text = script.Parent.CallsignFrame.CallsignInput.Text
	if Text:len() <= 4 then
		local dash = false
		for i = 1, Text:len() do
			local letter = Text:sub(i,i)
			if letter == "-" and dash == false then
				dash = true
				print("dash used")
			elseif dash == true and letter == "-" then
				print("already a dash")
				script.Parent.CallsignFrame.CallsignInput.Text = Text:gsub(letter, "")
			elseif not tonumber(letter) then
				script.Parent.CallsignFrame.CallsignInput.Text = Text:gsub(letter, "")
			end
		end
	else
		script.Parent.CallsignFrame.CallsignInput.Text = Text:sub(1,4)
	end
end)