How to determine whether my code is running in a lua module?

Question

I am writing a script testmodule.lua and want to check that if this file is imported/required from another script or directly started by lua testmodule.lua.

If it is directly started by command line I can do some test or run a main function, otherwise just export some function and do nothing.

Python has a __name__ statement:

if __name__ == '__main__':
    main_entry()

Is there something similar in lua ??

It is useful to write a shell util in a single file, which can be run directly and imported by other lua scripts. But when some script import this file, I don't like main function to be called.

Does this answer your question? ["main" function in Lua?](https://stackoverflow.com/questions/4521085/main-function-in-lua) — mrkskwsnck, Dec 01 '19 at 21:01

score 11 · Accepted Answer · answered Mar 20 '18 at 05:20

11

You can use the following check:

if pcall(debug.getlocal, 4, 1) then
  print("in package")
else
  print("in main script")
end

It checks if there is anything in the 1st variable at the 4th level, which would be the caller of the current module (if required) or nothing in the case of the main script.

Note that it doesn't distinguish between require, dofile, loadfile or other similar calls. You may want to check this recent thread on the Lua mail list that discusses checking for these calls and some alternative ways as well.

answered Mar 20 '18 at 05:20

Paul Kulchenko

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Thanks a lot, I would like to upvote this but I have not got enough reputation. – skywind3000 Mar 20 '18 at 05:46
You can always accept the answer if it worked for you. – Paul Kulchenko Mar 20 '18 at 14:45
1

Is there a particular reason that you used `pcall(debug.getlocal, 4, 1)` rather than simply calling it as `debug.getlocal(4, 1)`? – The Elemental of Destruction Aug 19 '19 at 02:31
1

It's because you may get `bad argument #1 to 'getlocal' (level out of range)` when called from a script. You probably don't want to terminate the script on this check. – Paul Kulchenko Aug 19 '19 at 03:21
seems check `debug.getinfo(4)` not nil can be tested without `pcall` – yurenchen Oct 18 '22 at 19:39

How to determine whether my code is running in a lua module?

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