Excluding files from git-diff

I am tracking a project with git. There are some Xcode project files in the working copy that I want to keep tracking, but do not want to see in diffs, because there are always dozens of changed lines that I am never interested in. Is there a simple way to have git-diff skip these files? I’ve tried to set up a custom “silent” diff tool:

$ cat .gitattributes 
Project.xcodeproj/* diff=nodiff

$ cat ~/.gitconfig 
[diff "nodiff"]
    command = /bin/true

But:

$ git diff
external diff died, stopping at Project.xcodeproj/zoul.mode1v3.

What am I doing wrong?

The problem is that /bin/true will return immediately without reading its input. git diff therefore thinks, quite reasonably, that it has died prematurely.

What you really want to do is to unset the diff attribute, not set it to a bogus command. Try this in your .gitattributes:

Project.xcodeproj/* -diff

You may use an alias in your .git/config

[alias]
        mydiff = !git diff | filterdiff -x "*/Project.xcodeproj/*"

You need filterdiff (from patchutils) for this trick.

sudo apt-get install patchutils

Still the diff isn't perfect, it leaves some garbage :

yannick@yannick-desktop:~/git-filter-test$ git mydiff
diff --git a/Project.xcodeproj/dummy.txt b/Project.xcodeproj/dummy.txt
index 3e1f9e6..89dfed9 100644
diff --git a/dummy2.txt b/dummy2.txt
index 91966ce..d9588a9 100644
--- a/titi.txt
+++ b/titi.txt
@@ -1,3 +1,3 @@
 aaaaaaaaaa
-bbbbbbbbb
 cccccc
+ddd

Another solution that produces clean output without any external tools (add to .git/config):

[alias]
    mydiff = !git diff -- $(git diff --name-only | grep -Ev "Project.xcodeproj/")

Then run it with:

git mydiff

Note that git diff --name-only is better than git ls-files because it will pass a shorter list of files to git diff, since only files that are modified will be included. I've run into trouble with exceeding the maximum number of arguments in large projects when using git ls-files.