NAME
git-read-tree - Reads tree information into the indexSYNOPSIS
git read-tree [(-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>) [-u | -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. When used with -u, updates leading to
loss of working tree changes or untracked files or directories will not abort
the operation.
-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 or 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.
--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-]recurse-submodules
Using --recurse-submodules will update the
content of all active submodules according to the commit recorded in the
superproject by calling read-tree recursively, also setting the submodules'
HEAD to be detached at that commit.
--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.
-q, --quiet
Quiet, suppress feedback messages.
<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 or more 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
Note: The skip-worktree capabilities in git-update-index(1) and read-tree predated the introduction of git-sparse-checkout(1). Users are encouraged to use the sparse-checkout command in preference to these plumbing commands for sparse-checkout/skip-worktree related needs. However, the information below might be useful to users trying to understand the pattern style used in non-cone mode of the sparse-checkout command./* !unwanted
/*
SEE ALSO
git-write-tree(1), git-ls-files(1), gitignore(5), git-sparse-checkout(1)GIT
Part of the git(1) suite02/28/2023 | Git 2.39.2 |