Error while changing the default application with which we open a file

Question

Recently I've tried to change the default application with which a file is opened, by doing the following:

1. Right click on the file

2. Get info

3. In "Open with", change to the application you want your file to be opened with.

4. Click on the "Change All" button which is found under the "Open with" label

in the last step, i.e. when I click on "Change All", I receive the following message:

then if I look at the default application that opens this file, it's really the application I've just chosen, but when I click on the file to open it, I've the following error message:

Yes, I was trying to open a Makefile for a C program.

Any ideas of why this is happening and how to solve it?

Answer 1

I had the same problem, with a set of files that do have an extension (testfile.py). It turned out that there was an (invisible to me) space at the end of the filename "testfile.py ", which was causing the headache. i removed that, and all was fine again.

Answer 2

The error that you see is just a security measure of macOS because you probably downloaded some source code from the internet, to compile, of which 'Makefile' is a part of. It's just asking you to be careful and be sure that it is not a malware.

To remove this warning, execute the following command in Terminal on the folder where the code is:

sudo xattr -r -d com.apple.quarantine /path/to/folder/where/code/is

The 'com.apple.quarantine' is a metadata that macOS adds to files downloaded from the internet. This triggers the warning in macOS. Executing the above command removes this metadata from the folder and all files inside it, and thus macOS will henceforth treat all the files as normal (or "safe / trusted").