git-read-tree(1)
================
-v0.1, May 2005
NAME
----
-git-read-tree - Reads tree information into the directory cache
+git-read-tree - Reads tree information into the index
SYNOPSIS
--------
-'git-read-tree' (<tree-ish> | [-m [-u|-i]] <tree-ish1> [<tree-ish2> [<tree-ish3>]])
+'git-read-tree' (<tree-ish> | [[-m [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] <tree-ish1> [<tree-ish2> [<tree-ish3>]])
DESCRIPTION
-----------
-Reads the tree information given by <tree-ish> into the directory cache,
+Reads the tree information given by <tree-ish> into the index,
but does not actually *update* any of the files it "caches". (see:
-git-checkout-index)
+gitlink:git-checkout-index[1])
-Optionally, it can merge a tree into the cache, perform a
-fast-forward (i.e. 2-way) merge, or a 3-way merge, with the -m
-flag. When used with -m, the -u flag causes it to also update
+Optionally, it can merge a tree into the index, perform a
+fast-forward (i.e. 2-way) merge, or a 3-way merge, with the `-m`
+flag. When used with `-m`, the `-u` flag causes it to also update
the files in the work tree with the result of the merge.
-Trivial merges are done by "git-read-tree" itself. Only conflicting paths
-will be in unmerged state when "git-read-tree" returns.
+Trivial merges are done by `git-read-tree` itself. Only conflicting paths
+will be in unmerged state when `git-read-tree` returns.
OPTIONS
-------
-m::
- Perform a merge, not just a read.
+ Perform a merge, not just a read. The command will
+ refuse to run if your index file has unmerged entries,
+ indicating that you have not finished previous merge you
+ started.
+
+--reset::
+ Same as -m, except that unmerged entries are discarded
+ instead of failing.
-u::
After a successful merge, update the files in the work
trees that are not directly related to the current
working tree status into a temporary index file.
+--aggressive::
+ Usually a three-way merge by `git-read-tree` resolves
+ the merge for really trivial cases and leaves other
+ cases unresolved in the index, so that Porcelains can
+ implement different merge policies. This flag makes the
+ command to resolve a few more cases internally:
++
+* when one side removes a path and the other side leaves the path
+ unmodified. The resolution is to remove that path.
+* when both sides remove a path. The resolution is to remove that path.
+* when both sides adds a path identically. The resolution
+ is to add that path.
+
+--prefix=<prefix>/::
+ Keep the current index contents, and read the contents
+ of named tree-ish under directory at `<prefix>`. The
+ original index file cannot have anything at the path
+ `<prefix>` itself, and have nothing in `<prefix>/`
+ directory. Note that the `<prefix>/` value must end
+ with a slash.
+
<tree-ish#>::
The id of the tree object(s) to be read/merged.
Merging
-------
-If '-m' is specified, "git-read-tree" can perform 3 kinds of
+If `-m` is specified, `git-read-tree` can perform 3 kinds of
merge, a single tree merge if only 1 tree is given, a
fast-forward merge with 2 trees, or a 3-way merge if 3 trees are
provided.
Single Tree Merge
~~~~~~~~~~~~~~~~~
If only 1 tree is specified, git-read-tree operates as if the user did not
-specify '-m', except that if the original cache has an entry for a
+specify `-m`, except that if the original index has an entry for a
given pathname, and the contents of the path matches with the tree
-being read, the stat info from the cache is used. (In other words, the
-cache's stat()s take precedence over the merged tree's).
+being read, the stat info from the index is used. (In other words, the
+index's stat()s take precedence over the merged tree's).
-That means that if you do a "git-read-tree -m <newtree>" followed by a
-"git-checkout-index -f -u -a", the "git-checkout-index" only checks out
+That means that if you do a `git-read-tree -m <newtree>` followed by a
+`git-checkout-index -f -u -a`, the `git-checkout-index` only checks out
the stuff that really changed.
-This is used to avoid unnecessary false hits when "git-diff-files" is
-run after git-read-tree.
+This is used to avoid unnecessary false hits when `git-diff-files` is
+run after `git-read-tree`.
Two Tree Merge
~~~~~~~~~~~~~~
-Typically, this is invoked as "git-read-tree -m $H $M", where $H
+Typically, this is invoked as `git-read-tree -m $H $M`, where $H
is the head commit of the current repository, and $M is the head
of a foreign tree, which is simply ahead of $H (i.e. we are in a
fast forward situation).
When two trees are specified, the user is telling git-read-tree
the following:
- (1) The current index and work tree is derived from $H, but
+ 1. The current index and work tree is derived from $H, but
the user may have local changes in them since $H;
- (2) The user wants to fast-forward to $M.
+ 2. The user wants to fast-forward to $M.
-In this case, the "git-read-tree -m $H $M" command makes sure
+In this case, the `git-read-tree -m $H $M` command makes sure
that no local change is lost as the result of this "merge".
Here are the "carry forward" rules:
-------------------------------------------------------
0 nothing nothing nothing (does not happen)
1 nothing nothing exists use M
- 2 nothing exists nothing remove path from cache
+ 2 nothing exists nothing remove path from index
3 nothing exists exists use M
clean I==H I==M
8 yes N/A no nothing exists fail
9 no N/A no nothing exists fail
- 10 yes yes N/A exists nothing remove path from cache
+ 10 yes yes N/A exists nothing remove path from index
11 no yes N/A exists nothing fail
12 yes no N/A exists nothing fail
13 no no N/A exists nothing fail
20 yes yes no exists exists use M
21 no yes no exists exists fail
-In all "keep index" cases, the cache entry stays as in the
+In all "keep index" cases, the index entry stays as in the
original index file. If the entry were not up to date,
git-read-tree keeps the copy in the work tree intact when
operating under the -u flag.
When this form of git-read-tree returns successfully, you can
see what "local changes" you made are carried forward by running
-"git-diff-index --cached $M". Note that this does not
-necessarily match "git-diff-index --cached $H" would have
+`git-diff-index --cached $M`. Note that this does not
+necessarily match `git-diff-index --cached $H` would have
produced before such a two tree merge. This is because of cases
18 and 19 --- if you already had the changes in $M (e.g. maybe
-you picked it up via e-mail in a patch form), "git-diff-index
---cached $H" would have told you about the change before this
-merge, but it would not show in "git-diff-index --cached $M"
+you picked it up via e-mail in a patch form), `git-diff-index
+--cached $H` would have told you about the change before this
+merge, but it would not show in `git-diff-index --cached $M`
output after two-tree merge.
Each "index" entry has two bits worth of "stage" state. stage 0 is the
normal one, and is the only one you'd see in any kind of normal use.
-However, when you do "git-read-tree" with three trees, the "stage"
+However, when you do `git-read-tree` with three trees, the "stage"
starts out at 1.
This means that you can do
- git-read-tree -m <tree1> <tree2> <tree3>
+----------------
+$ git-read-tree -m <tree1> <tree2> <tree3>
+----------------
and you will end up with an index with all of the <tree1> entries in
"stage1", all of the <tree2> entries in "stage2" and all of the
-<tree3> entries in "stage3".
+<tree3> entries in "stage3". When performing a merge of another
+branch into the current branch, we use the common ancestor tree
+as <tree1>, the current branch head as <tree2>, and the other
+branch head as <tree3>.
-Furthermore, "git-read-tree" has special-case logic that says: if you see
+Furthermore, `git-read-tree` has special-case logic that says: if you see
a file that matches in all respects in the following states, it
"collapses" back to "stage0":
- stage 2 and 3 are the same; take one or the other (it makes no
- difference - the same work has been done on stage 2 and 3)
+ difference - the same work has been done on our branch in
+ stage 2 and their branch in stage 3)
- stage 1 and stage 2 are the same and stage 3 is different; take
- stage 3 (some work has been done on stage 3)
+ stage 3 (our branch in stage 2 did not do anything since the
+ ancestor in stage 1 while their branch in stage 3 worked on
+ it)
- stage 1 and stage 3 are the same and stage 2 is different take
- stage 2 (some work has been done on stage 2)
+ stage 2 (we did something while they did nothing)
-The "git-write-tree" command refuses to write a nonsensical tree, and it
+The `git-write-tree` command refuses to write a nonsensical tree, and it
will complain about unmerged entries if it sees a single entry that is not
stage 0.
-Ok, this all sounds like a collection of totally nonsensical rules,
+OK, this all sounds like a collection of totally nonsensical rules,
but it's actually exactly what you want in order to do a fast
merge. The different stages represent the "result tree" (stage 0, aka
"merged"), the original tree (stage 1, aka "orig"), and the two trees
- the index file saves and restores with all this information, so you
can merge things incrementally, but as long as it has entries in
- stages 1/2/3 (ie "unmerged entries") you can't write the result. So
+ stages 1/2/3 (i.e., "unmerged entries") you can't write the result. So
now the merge algorithm ends up being really simple:
* you walk the index in order, and ignore all entries of stage 0,
matching "stage1" entry if it exists too. .. all the normal
trivial rules ..
-You would normally use "git-merge-index" with supplied
-"git-merge-one-file" to do this last step. The script
-does not touch the files in the work tree, and the entire merge
-happens in the index file. In other words, there is no need to
-worry about what is in the working directory, since it is never
-shown and never used.
+You would normally use `git-merge-index` with supplied
+`git-merge-one-file` to do this last step. The script updates
+the files in the working tree as it merges each path and at the
+end of a successful merge.
When you start a 3-way merge with an index file that is already
populated, it is assumed that it represents the state of the
file that does not match stage 2.
This is done to prevent you from losing your work-in-progress
-changes. To illustrate, suppose you start from what has been
-commited last to your repository:
+changes, and mixing your random changes in an unrelated merge
+commit. To illustrate, suppose you start from what has been
+committed last to your repository:
- $ JC=`cat .git/HEAD`
- $ git-checkout-index -f -u -a $JC
+----------------
+$ JC=`git-rev-parse --verify "HEAD^0"`
+$ git-checkout-index -f -u -a $JC
+----------------
You do random edits, without running git-update-index. And then
you notice that the tip of your "upstream" tree has advanced
since you pulled from him:
- $ git-fetch rsync://.... linus
- $ LT=`cat .git/MERGE_HEAD`
+----------------
+$ git-fetch git://.... linus
+$ LT=`cat .git/FETCH_HEAD`
+----------------
Your work tree is still based on your HEAD ($JC), but you have
some edits since. Three-way merge makes sure that you have not
-added or modified cache entries since $JC, and if you haven't,
+added or modified index entries since $JC, and if you haven't,
then does the right thing. So with the following sequence:
- $ git-read-tree -m -u `git-merge-base $JC $LT` $JC $LT
- $ git-merge-index git-merge-one-file -a
- $ echo "Merge with Linus" | \
- git-commit-tree `git-write-tree` -p $JC -p $LT
+----------------
+$ git-read-tree -m -u `git-merge-base $JC $LT` $JC $LT
+$ git-merge-index git-merge-one-file -a
+$ echo "Merge with Linus" | \
+ git-commit-tree `git-write-tree` -p $JC -p $LT
+----------------
-what you would commit is a pure merge between $JC and LT without
+what you would commit is a pure merge between $JC and $LT without
your work-in-progress changes, and your work tree would be
updated to the result of the merge.
+However, if you have local changes in the working tree that
+would be overwritten by this merge,`git-read-tree` will refuse
+to run to prevent your changes from being lost.
+
+In other words, there is no need to worry about what exists only
+in the working tree. When you have local changes in a part of
+the project that is not involved in the merge, your changes do
+not interfere with the merge, and are kept intact. When they
+*do* interfere, the merge does not even start (`git-read-tree`
+complains loudly and fails without modifying anything). In such
+a case, you can simply continue doing what you were in the
+middle of doing, and when your working tree is ready (i.e. you
+have finished your work-in-progress), attempt the merge again.
+
See Also
--------