in your git archive. We'll start off with a few bad examples, just to
get a feel for how this works:
- echo "Hello World" > a
- echo "Silly example" > b
+ echo "Hello World" >hello
+ echo "Silly example" >example
you have now created two files in your working directory, but to
actually check in your hard work, you will have to go through two steps:
So to populate the index with the two files you just created, you can do
- git-update-cache --add a b
+ git-update-cache --add hello example
and you have now told git to track those two files.
git-cat-file "blob" 557db03de997c86a4a028e1ebd3a1ceb225be238
which will print out "Hello World". The object 557db... is nothing
-more than the contents of your file "a".
+more than the contents of your file "hello".
-[ Digression: don't confuse that object with the file "a" itself. The
+[ Digression: don't confuse that object with the file "hello" itself. The
object is literally just those specific _contents_ of the file, and
- however much you later change the contents in file "a", the object we
+ however much you later change the contents in file "hello", the object we
just looked at will never change. Objects are immutable. ]
Anyway, as we mentioned previously, you normally never actually take a
most basic git commands to manipulate the files or look at their status.
In particular, let's not even check in the two files into git yet, we'll
-start off by adding another line to "a" first:
+start off by adding another line to "hello" first:
- echo "It's a new day for git" >> a
+ echo "It's a new day for git" >>hello
-and you can now, since you told git about the previous state of "a", ask
+and you can now, since you told git about the previous state of "hello", ask
git what has changed in the tree compared to your old index, using the
"git-diff-files" command:
oops. That wasn't very readable. It just spit out its own internal
version of a "diff", but that internal version really just tells you
-that it has noticed that "a" has been modified, and that the old object
+that it has noticed that "hello" has been modified, and that the old object
contents it had have been replaced with something else.
To make it readable, we can tell git-diff-files to output the
which will spit out
- diff --git a/a b/a
- --- a/a
- +++ b/a
+ diff --git a/hello b/hello
+ --- a/hello
+ +++ b/hello
@@ -1 +1,2 @@
Hello World
+It's a new day for git
-ie the diff of the change we caused by adding another line to "a".
+ie the diff of the change we caused by adding another line to "hello".
In other words, git-diff-files always shows us the difference between
what is recorded in the index, and what is currently in the working
and this will just output the name of the resulting tree, in this case
(if you have does exactly as I've described) it should be
- 3ede4ed7e895432c0a247f09d71a76db53bd0fa4
+ 8988da15d077d4829fc51d8544c097def6644dbb
which is another incomprehensible object name. Again, if you want to,
-you can use "git-cat-file -t 3ede4.." to see that this time the object
+you can use "git-cat-file -t 8988d.." to see that this time the object
is not a "blob" object, but a "tree" object (you can also use
git-cat-file to actually output the raw object contents, but you'll see
mainly a binary mess, so that's less interesting).
which will say:
- Committing initial tree 3ede4ed7e895432c0a247f09d71a76db53bd0fa4
+ Committing initial tree 8988da15d077d4829fc51d8544c097def6644dbb
just to warn you about the fact that it created a totally new commit
that is not related to anything else. Normally you do this only _once_
Making a change
---------------
-Remember how we did the "git-update-cache" on file "a" and then we
-changed "a" afterward, and could compare the new state of "a" with the
+Remember how we did the "git-update-cache" on file "hello" and then we
+changed "hello" afterward, and could compare the new state of "hello" with the
state we saved in the index file?
Further, remember how I said that "git-write-tree" writes the contents
of the _index_ file to the tree, and thus what we just committed was in
-fact the _original_ contents of the file "a", not the new ones. We did
+fact the _original_ contents of the file "hello", not the new ones. We did
that on purpose, to show the difference between the index state, and the
state in the working directory, and how they don't have to match, even
when we commit things.
work through the index file, so the first thing we need to do is to
update the index cache:
- git-update-cache a
+ git-update-cache hello
(note how we didn't need the "--add" flag this time, since git knew
about the file already).
Note what happens to the different git-diff-xxx versions here. After
-we've updated "a" in the index, "git-diff-files -p" now shows no
+we've updated "hello" in the index, "git-diff-files -p" now shows no
differences, but "git-diff-cache -p HEAD" still _does_ show that the
current state is different from the state we committed. In fact, now
"git-diff-cache" shows the same difference whether we use the "--cached"
flag or not, since now the index is coherent with the working directory.
-Now, since we've updated "a" in the index, we can commit the new
+Now, since we've updated "hello" in the index, we can commit the new
version. We could do it by writing the tree by hand again, and
committing the tree (this time we'd have to use the "-p HEAD" flag to
tell commit that the HEAD was the _parent_ of the new commit, and that
mkdir my-git
cd my-git
- rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ my-git .git
+ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
followed by
that branch, and do some work there.
git checkout mybranch
- echo "Work, work, work" >> a
- git commit a
+ echo "Work, work, work" >>hello
+ git commit hello
-Here, we just added another line to "a", and we used a shorthand for
-both going a "git-update-cache a" and "git commit" by just giving the
-filename directly to "git commit".
+Here, we just added another line to "hello", and we used a shorthand for
+both going a "git-update-cache hello" and "git commit" by just giving the
+filename directly to "git commit".
Now, to make it a bit more interesting, let's assume that somebody else
does some work in the original branch, and simulate that by going back
git checkout master
-Here, take a moment to look at the contents of "a", and notice how they
+Here, take a moment to look at the contents of "hello", and notice how they
don't contain the work we just did in "mybranch" - because that work
hasn't happened in the "master" branch at all. Then do
- echo "Play, play, play" >> a
- echo "Lots of fun" >> b
- git commit a b
+ echo "Play, play, play" >>hello
+ echo "Lots of fun" >>example
+ git commit hello example
since the master branch is obviously in a much better mood.
file, which had no differences in the "mybranch" branch), and say:
Simple merge failed, trying Automatic merge
- Auto-merging a.
+ Auto-merging hello.
merge: warning: conflicts during merge
- ERROR: Merge conflict in a.
+ ERROR: Merge conflict in hello.
fatal: merge program failed
Automatic merge failed, fix up by hand
which is way too verbose, but it basically tells you that it failed the
really trivial merge ("Simple merge") and did an "Automatic merge"
-instead, but that too failed due to conflicts in "a".
+instead, but that too failed due to conflicts in "hello".
-Not to worry. It left the (trivial) conflict in "a" in the same form you
+Not to worry. It left the (trivial) conflict in "hello" in the same form you
should already be well used to if you've ever used CVS, so let's just
-open "a" in our editor (whatever that may be), and fix it up somehow.
-I'd suggest just making it so that "a" contains all four lines:
+open "hello" in our editor (whatever that may be), and fix it up somehow.
+I'd suggest just making it so that "hello" contains all four lines:
Hello World
It's a new day for git
and once you're happy with your manual merge, just do a
- git commit a
+ git commit hello
which will very loudly warn you that you're now committing a merge
(which is correct, so never mind), and you can write a small merge
projects / git.git / commitdiff