I was trying to perform git clean for some untracked files. I typed the following, unintentionally right, command:
git clean -dn | grep -v <files_to_exclude> | git clean -df
Note that the line seems to be missing a xargs. That is, I'd have normally written the previous command like this:
git clean -df | grep -v <files_to_exclude> | xargs git clean -df --
That being said, the former worked and the latter didn't! Yes, I know I could have just used:
git clean -df --exclude=<files_to_exclude>
I didn't know about the exclude option back then.
Just to make sure you have the right picture, let's say you have three untracked files x, y, and z and you are to exclude x.
$ git clean -dn | grep -v x
Would remove y
Would remove z
It makes sense the plumbing this output to xargs directly without omitting "Would remove " part is wrong and will cause git clean to break.
Now the question is: why did it work with plumbing this output directly to git clean it still worked?
git clean -df <no extra args>, which cleans all the files, not just the ones you wanted to include ...grep will actually match full messages instead of file names, so running grep -v Would for example excludes all lines, and if the output is empty, you fall back on git clean -df which once again removes all instead of nothing ....)