debug.sethook()

debug.sethook ([thread,] hook, mask [, count])

Sets the given function as a hook. The string mask and the number count describe when the hook will be called. The string mask may have any combination of the following characters, with the given meaning:

• 'c': the hook is called every time Lua calls a function;
• 'r': the hook is called every time Lua returns from a function;
• 'l': the hook is called every time Lua enters a new line of code.

Moreover, with a count different from zero, the hook is called also after every count instructions.

When called without arguments, debug.sethook turns off the hook.

When the hook is called, its first parameter is a string describing the event that has triggered its call: "call" (or "tail call"), "return", "line", and "count". For line events, the hook also gets the new line number as its second parameter. Inside a hook, you can call getinfo with level 2 to get more information about the running function (level 0 is the getinfo function, and level 1 is the hook function).