How would I print out errors? - error-handling

Question

In the software called Roblox studio I need help making a script that whenever an error happens in game, it would print out the error again using the normal print function something like this example here:
Local error = —-whatever the error that happened was
Print(error) —- so it just simply prints it back out

Answer 1

Roblox provides a few different ways to keep track of when errors are thrown in your Scripts and LocalScripts.
If you want to observe errors locally in a script, and you know a specific chunk of code may throw errors, you can use pcall() as a try-catch block.
local success, result = pcall(function()
error("this is a test error message")
end)
if not success then
print("An error was thrown!")
print(result) --"this is a test error message"
end
If you want to observe errors across all of your scripts, you can attach a callback to the ScriptContext.Error signal. This signal fires any time any error is thrown. It provides information about the error, including the message, the callstack, and a reference to the script that threw the error.
Warning : ScriptContext.Error only fires in the context of the script that registers it. A Script will only observe errors thrown in server scripts, and registering in a LocalScript will only observe errors thrown on the client.
local ScriptContext = game:GetService("ScriptContext")
ScriptContext.Error:Connect( function(message, stack, context)
print("An error was thrown!")
print("Message : ", message)
print("Stack : ", stack)
print("Context :", context:GetFullName())
end)
Similarly, if you only care about the error messages themselves, you can also observe them being printed out to the Output window using the LogService.MessageOut signal. This signal fires any time anything is logged to Output. This includes messages, warnings, and errors.
local LogService = game:GetService("LogService")
LogService.MessageOut:Connect( function(message, messageType)
if messageType == Enum.MessageType.MessageError then
print("An error was thrown!")
print(message)
end
end)

Answer 2

Use the stderr stream from io library to print debug messages.
-- Define debug function based in print
function debug(...) io.stderr:write(table.concat({...}, '\9') .. '\n') end
-- Debug acts as a regular "print()", but it writes to stderr instead
debug('[filename.lua]', 'debug')
Use "error()" function to print errors.
if true then
error("It should not be true!")
end
If you want to catch errors from a function, use xpcall()
-- Define debug
function debug(...) io.stderr:write(table.concat({...}, '\9') .. '\n') end
xpcall(
function()
local b = {}
-- This will throw an error because you cant index nil values
print(a.b)
end,
function(err)
debug('[xpcall]', err)
end
)
xpcall() wont stop the execution in case of error, so you only need to encapsulate your code in it if you want to catch any unexpected errors at runtime.