How to prevent MacOS from adding dot underscore files (._whatever.html )in zip archives?

Question

Our organisation receives zip files from Mac users which contain a ._ file in addition to the file we expect. In the past this was due to resource fork and data fork encoding limitations on other file systems. So for example, when we expect a submission that looks like this:

README.md
src/mysite.html
src/myscript.js

we generally receive a zip that contains files such as:

._README.md
README.md
src/._mysite.html
src/mysite.html
src/._myscript.js
src/myscript.js

This makes it difficult for us to process these files automatically. What instructions should we give to our Mac users to suppress these files we can’t process or handle?

Answer 1

There's no native way to automatically exclude resource forks or other extended attribute and filesystem metadata during compression, but many 3rd party apps can do it. These files contain filesystem data that should be preserved and you get a valuable signal that you have lost data when your process strips or ignores these files.

One such is Keka (donationware, ie free direct download, paid from App Store)

Answer 2

No, it is not possible to prevent the creation of resource fork files - the native zip function is designed to preserve this filesystem specific data so you would need to instruct your team to use a different tool or process.

It will likely be easier to improve your tooling to ignore files it knows are safe to ignore than to force a change in the behaviour of your users.

dot_clean on macOS

Instead, clean the files before ingesting them with macOS's dot_clean:

For each dir, dot_clean recursively merges all ._* files with their corresponding native files according to the rules specified with the given arguments. By default, if there is an attribute on the native file that is also present in the ._ file, the most recent attribute will be used.

find on Linux

On Linux, use find to recursively remove all the matching files:

find  . -type f -name '\._*' -exec rm {} \;

Answer 3

Yes!

I faced this problem for some time using bootloaders on embedded devices that use the USB Mass Storage Class. Adding these tracking files will usually corrupt the firmware and it's really frustrating. But there is a solution.

First, when opening the drive do not navigate there in Finder AT ALL. Don't open it. Don't look at it. Don't do anything.

Second, open Terminal. We're going to use the cp command to copy the files. However, the key here is the -X option which for macOS will prevent the addition of the resource files.

For example:

cp -X lpc11u35_gr_mango_if_crc_20200717.bin /Volumes/CRP\ DISABLD/

Bingo! No dot-underscore file. No .DS_Store. Nothing, nada, zip, zilch. I know it's tedious to have to go to the terminal, but in cases like this it's a lot better than having a Windows or Linux VM on standby for stupid issues like this.