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GIT-READ-TREE(1) | Git Manual | GIT-READ-TREE(1) |
NAME¶
git-read-tree - Reads tree information into the indexSYNOPSIS¶
git read-tree [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] [-u [--exclude-per-directory=<gitignore>] | -i]] [--index-output=<file>] [--no-sparse-checkout] (--empty | <tree-ish1> [<tree-ish2> [<tree-ish3>]])
DESCRIPTION¶
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(1))OPTIONS¶
-mPerform 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 tree with the result of the merge.
-i
Usually a merge requires the index file as
well as the files in the working tree to be up to date with the current head
commit, in order not to lose local changes. This flag disables the check with
the working tree and is meant to be used when creating a merge of trees that
are not directly related to the current working tree status into a temporary
index file.
-n, --dry-run
Check if the command would error out, without
updating the index nor the files in the working tree for real.
-v
Show the progress of checking files out.
--trivial
Restrict three-way merge by git
read-tree to happen only if there is no file-level merging required,
instead of resolving merge for trivial cases and leaving conflicting files
unresolved in the index.
--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 resolve a few more cases
internally:
--prefix=<prefix>/
•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 add a path identically.
The resolution is to add that path.
Keep the current index contents, and read the
contents of the named tree-ish under the directory at <prefix>. The
command will refuse to overwrite entries that already existed in the original
index file. Note that the <prefix>/ value must end with a slash.
--exclude-per-directory=<gitignore>
When running the command with -u and -m
options, the merge result may need to overwrite paths that are not tracked in
the current branch. The command usually refuses to proceed with the merge to
avoid losing such a path. However this safety valve sometimes gets in the way.
For example, it often happens that the other branch added a file that used to
be a generated file in your branch, and the safety valve triggers when you try
to switch to that branch after you ran make but before running make clean to
remove the generated file. This option tells the command to read per-directory
exclude file (usually .gitignore) and allows such an untracked but
explicitly ignored file to be overwritten.
--index-output=<file>
Instead of writing the results out to
$GIT_INDEX_FILE, write the resulting index in the named file. While the
command is operating, the original index file is locked with the same
mechanism as usual. The file must allow to be rename(2)ed into from a
temporary file that is created next to the usual index file; typically this
means it needs to be on the same filesystem as the index file itself, and you
need write permission to the directories the index file and index output file
are located in.
--no-sparse-checkout
Disable sparse checkout support even if
core.sparseCheckout is true.
--empty
Instead of reading tree object(s) into the
index, just empty it.
<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 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 index has an entry for a given pathname, and the contents of the path match with the tree 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).Two Tree Merge¶
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). 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 $M.
I H M Result ------------------------------------------------------- 0 nothing nothing nothing (does not happen) 1 nothing nothing exists use M 2 nothing exists nothing remove path from index 3 nothing exists exists, use M if "initial checkout", H == M keep index otherwise exists, fail H != M
clean I==H I==M ------------------ 4 yes N/A N/A nothing nothing keep index 5 no N/A N/A nothing nothing keep index
6 yes N/A yes nothing exists keep index 7 no N/A yes nothing exists keep index 8 yes N/A no nothing exists fail 9 no N/A no nothing exists fail
10 yes yes N/A exists nothing remove path from index 11 no yes N/A exists nothing fail 12 yes no N/A exists nothing fail 13 no no N/A exists nothing fail
clean (H==M) ------ 14 yes exists exists keep index 15 no exists exists keep index
clean I==H I==M (H!=M) ------------------ 16 yes no no exists exists fail 17 no no no exists exists fail 18 yes no yes exists exists keep index 19 no no yes exists exists keep index 20 yes yes no exists exists use M 21 no yes no exists exists fail
3-Way Merge¶
Each "index" entry has two bits worth of "stage" state. stage 0 is the normal one, and is the only one you’d see in any kind of normal use.$ git read-tree -m <tree1> <tree2> <tree3>
•stage 2 and 3 are the same; take one or
the other (it makes no 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 (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 (we did something while they did
nothing)
•if a file exists in identical format in
all three trees, it will automatically collapse to "merged" state by
git read-tree.
•a file that has any difference
what-so-ever in the three trees will stay as separate entries in the index.
It’s up to "porcelain policy" to determine how to remove the
non-0 stages, and insert a merged version.
•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 (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, since they’ve already been done.
•if you find a "stage1", but
no matching "stage2" or "stage3", you know it’s been
removed from both trees (it only existed in the original tree), and you remove
that entry.
•if you find a matching
"stage2" and "stage3" tree, you remove one of them, and
turn the other into a "stage0" entry. Remove any matching
"stage1" entry if it exists too. .. all the normal trivial rules
..
$ JC=`git rev-parse --verify "HEAD^0"` $ git checkout-index -f -u -a $JC
$ git fetch git://.... linus $ LT=`git rev-parse FETCH_HEAD`
$ 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
SPARSE CHECKOUT¶
"Sparse checkout" allows populating the working directory sparsely. It uses the skip-worktree bit (see git-update-index(1)) to tell Git whether a file in the working directory is worth looking at./* !unwanted
/*
SEE ALSO¶
git-write-tree(1); git-ls-files(1); gitignore(5)GIT¶
Part of the git(1) suite04/08/2014 | Git 1.9.1 |