Is there a way in lua to define a function that will run if a file is required?

Question

I would like to create a lua function early in a script that will then automatically get called if a matching filename is required but before that require is complete.

effectively it will go

if FILE then
   run before FILE is loaded
end

-- some other stuff

require"FILE"

If FILE is never required then the stuff in the if will never run

Answer 1

require is just a function so you can redefine it.

$ cat foo.lua
real_require = require

function require(mod)
    if mod == 'string' then
        -- do something
        print('importing ' .. mod)
    end

    return real_require(mod)
end

require'string'
$ lua foo.lua
importing string
$