1 GIT-READ-TREE(1) Git Manual GIT-READ-TREE(1)
6 git-read-tree - Reads tree information into the index
8 S
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9 _
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\bt _
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\be [[-m [--trivial] [--aggressive] | --reset |
10 --prefix=<prefix>] [-u [--exclude-per-directory=<gitignore>] | -i]]
11 [--index-output=<file>] [--no-sparse-checkout] <tree-ish1> [<tree-ish2>
14 D
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15 Reads the tree information given by <tree-ish> into the index, but does
16 not actually u
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\be any of the files it "caches". (see: g
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\but
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17 i
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\bx(1))
19 Optionally, it can merge a tree into the index, perform a fast-forward
20 (i.e. 2-way) merge, or a 3-way merge, with the -m flag. When used with
21 -m, the -u flag causes it to also update the files in the work tree
22 with the result of the merge.
24 Trivial merges are done by _
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\be itself. Only conflicting paths
25 will be in unmerged state when _
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27 O
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29 Perform a merge, not just a read. The command will refuse to run if
30 your index file has unmerged entries, indicating that you have not
31 finished previous merge you started.
34 Same as -m, except that unmerged entries are discarded instead of
38 After a successful merge, update the files in the work tree with
39 the result of the merge.
42 Usually a merge requires the index file as well as the files in the
43 working tree are up to date with the current head commit, in order
44 not to lose local changes. This flag disables the check with the
45 working tree and is meant to be used when creating a merge of trees
46 that are not directly related to the current working tree status
47 into a temporary index file.
50 Show the progress of checking files out.
53 Restrict three-way merge by _
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\be to happen only if there
54 is no file-level merging required, instead of resolving merge for
55 trivial cases and leaving conflicting files unresolved in the
59 Usually a three-way merge by _
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\ba_
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\be resolves the merge for
60 really trivial cases and leaves other cases unresolved in the
61 index, so that Porcelains can implement different merge policies.
62 This flag makes the command to resolve a few more cases internally:
64 · when one side removes a path and the other side leaves the path
65 unmodified. The resolution is to remove that path.
67 · when both sides remove a path. The resolution is to remove that
70 · when both sides adds a path identically. The resolution is to
74 Keep the current index contents, and read the contents of named
75 tree-ish under directory at <prefix>. The original index file
76 cannot have anything at the path <prefix> itself, and have nothing
77 in <prefix>/ directory. Note that the <prefix>/ value must end with
80 --exclude-per-directory=<gitignore>
81 When running the command with -u and -m options, the merge result
82 may need to overwrite paths that are not tracked in the current
83 branch. The command usually refuses to proceed with the merge to
84 avoid losing such a path. However this safety valve sometimes gets
85 in the way. For example, it often happens that the other branch
86 added a file that used to be a generated file in your branch, and
87 the safety valve triggers when you try to switch to that branch
88 after you ran make but before running make clean to remove the
89 generated file. This option tells the command to read per-directory
90 exclude file (usually _
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91 explicitly ignored file to be overwritten.
94 Instead of writing the results out to $GIT_INDEX_FILE, write the
95 resulting index in the named file. While the command is operating,
96 the original index file is locked with the same mechanism as usual.
97 The file must allow to be rename(2)ed into from a temporary file
98 that is created next to the usual index file; typically this means
99 it needs to be on the same filesystem as the index file itself, and
100 you need write permission to the directories the index file and
101 index output file are located in.
104 Disable sparse checkout support even if core.sparseCheckout is
108 The id of the tree object(s) to be read/merged.
110 M
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111 If -m is specified, _
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\be can perform 3 kinds of merge, a
112 single tree merge if only 1 tree is given, a fast-forward merge with 2
113 trees, or a 3-way merge if 3 trees are provided.
115 S
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116 If only 1 tree is specified, _
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117 not specify -m, except that if the original index has an entry for a
118 given pathname, and the contents of the path match with the tree being
119 read, the stat info from the index is used. (In other words, the
120 index’s stat()s take precedence over the merged tree’s).
122 That means that if you do a git read-tree -m <newtree> followed by a
123 git checkout-index -f -u -a, the _
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124 stuff that really changed.
126 This is used to avoid unnecessary false hits when _
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127 after _
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129 T
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130 Typically, this is invoked as git read-tree -m $H $M, where $H is the
131 head commit of the current repository, and $M is the head of a foreign
132 tree, which is simply ahead of $H (i.e. we are in a fast-forward
135 When two trees are specified, the user is telling _
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138 1. The current index and work tree is derived from $H, but the user
139 may have local changes in them since $H.
141 2. The user wants to fast-forward to $M.
143 In this case, the git read-tree -m $H $M command makes sure that no
144 local change is lost as the result of this "merge". Here are the "carry
145 forward" rules, where "I" denotes the index, "clean" means that index
146 and work tree coincide, and "exists"/"nothing" refer to the presence of
147 a path in the specified commit:
149 +--+--------------+---------+---------------+-------------+
151 | | I | H | M | Result |
152 +--+--------------+---------+---------------+-------------+
154 |0 | nothing | nothing | nothing | (does not |
156 +--+--------------+---------+---------------+-------------+
158 |1 | nothing | nothing | exists | use M |
159 +--+--------------+---------+---------------+-------------+
161 |2 | nothing | exists | nothing | remove path |
162 | | | | | from index |
163 +--+--------------+---------+---------------+-------------+
165 |3 | nothing | exists | exists, H ==M | use M if |
166 | +--------------+ +---------------+ "initial |
167 | | | | | checkout", |
168 | | exists, H != | | fail | keep index |
169 | | M | | | otherwise |
170 +--+--------------+---------+---------------+-------------+
174 4 yes N/A N/A nothing nothing keep index
175 5 no N/A N/A nothing nothing keep index
177 6 yes N/A yes nothing exists keep index
178 7 no N/A yes nothing exists keep index
179 8 yes N/A no nothing exists fail
180 9 no N/A no nothing exists fail
182 10 yes yes N/A exists nothing remove path from index
183 11 no yes N/A exists nothing fail
184 12 yes no N/A exists nothing fail
185 13 no no N/A exists nothing fail
189 14 yes exists exists keep index
190 15 no exists exists keep index
192 clean I==H I==M (H!=M)
194 16 yes no no exists exists fail
195 17 no no no exists exists fail
196 18 yes no yes exists exists keep index
197 19 no no yes exists exists keep index
198 20 yes yes no exists exists use M
199 21 no yes no exists exists fail
201 In all "keep index" cases, the index entry stays as in the original
202 index file. If the entry is not up to date, _
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203 copy in the work tree intact when operating under the -u flag.
205 When this form of _
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206 of the "local changes" that you made were carried forward by running
207 git diff-index --cached $M. Note that this does not necessarily match
208 what git diff-index --cached $H would have produced before such a two
209 tree merge. This is because of cases 18 and 19 --- if you already had
210 the changes in $M (e.g. maybe you picked it up via e-mail in a patch
211 form), git diff-index --cached $H would have told you about the change
212 before this merge, but it would not show in git diff-index --cached $M
213 output after the two-tree merge.
215 Case 3 is slightly tricky and needs explanation. The result from this
216 rule logically should be to remove the path if the user staged the
217 removal of the path and then switching to a new branch. That however
218 will prevent the initial checkout from happening, so the rule is
219 modified to use M (new tree) only when the content of the index is
220 empty. Otherwise the removal of the path is kept as long as $H and $M
223 3
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224 Each "index" entry has two bits worth of "stage" state. stage 0 is the
225 normal one, and is the only one you’d see in any kind of normal use.
227 However, when you do _
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230 This means that you can do
232 $ git read-tree -m <tree1> <tree2> <tree3>
235 and you will end up with an index with all of the <tree1> entries in
236 "stage1", all of the <tree2> entries in "stage2" and all of the <tree3>
237 entries in "stage3". When performing a merge of another branch into the
238 current branch, we use the common ancestor tree as <tree1>, the current
239 branch head as <tree2>, and the other branch head as <tree3>.
241 Furthermore, _
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242 a file that matches in all respects in the following states, it
243 "collapses" back to "stage0":
245 · stage 2 and 3 are the same; take one or the other (it makes no
246 difference - the same work has been done on our branch in stage 2
247 and their branch in stage 3)
249 · stage 1 and stage 2 are the same and stage 3 is different; take
250 stage 3 (our branch in stage 2 did not do anything since the
251 ancestor in stage 1 while their branch in stage 3 worked on it)
253 · stage 1 and stage 3 are the same and stage 2 is different take
254 stage 2 (we did something while they did nothing)
256 The _
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257 will complain about unmerged entries if it sees a single entry that is
260 OK, this all sounds like a collection of totally nonsensical rules, but
261 it’s actually exactly what you want in order to do a fast merge. The
262 different stages represent the "result tree" (stage 0, aka "merged"),
263 the original tree (stage 1, aka "orig"), and the two trees you are
264 trying to merge (stage 2 and 3 respectively).
266 The order of stages 1, 2 and 3 (hence the order of three <tree-ish>
267 command line arguments) are significant when you start a 3-way merge
268 with an index file that is already populated. Here is an outline of how
271 · if a file exists in identical format in all three trees, it will
272 automatically collapse to "merged" state by _
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274 · a file that has _
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\by difference what-so-ever in the three trees will
275 stay as separate entries in the index. It’s up to "porcelain
276 policy" to determine how to remove the non-0 stages, and insert a
279 · the index file saves and restores with all this information, so you
280 can merge things incrementally, but as long as it has entries in
281 stages 1/2/3 (i.e., "unmerged entries") you can’t write the result.
282 So now the merge algorithm ends up being really simple:
284 · you walk the index in order, and ignore all entries of stage 0,
285 since they’ve already been done.
287 · if you find a "stage1", but no matching "stage2" or "stage3",
288 you know it’s been removed from both trees (it only existed in
289 the original tree), and you remove that entry.
291 · if you find a matching "stage2" and "stage3" tree, you remove
292 one of them, and turn the other into a "stage0" entry. Remove
293 any matching "stage1" entry if it exists too. .. all the normal
296 You would normally use _
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\bx with supplied _
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297 to do this last step. The script updates the files in the working tree
298 as it merges each path and at the end of a successful merge.
300 When you start a 3-way merge with an index file that is already
301 populated, it is assumed that it represents the state of the files in
302 your work tree, and you can even have files with changes unrecorded in
303 the index file. It is further assumed that this state is "derived" from
304 the stage 2 tree. The 3-way merge refuses to run if it finds an entry
305 in the original index file that does not match stage 2.
307 This is done to prevent you from losing your work-in-progress changes,
308 and mixing your random changes in an unrelated merge commit. To
309 illustrate, suppose you start from what has been committed last to your
312 $ JC=‘git rev-parse --verify "HEAD^0"‘
313 $ git checkout-index -f -u -a $JC
316 You do random edits, without running _
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317 notice that the tip of your "upstream" tree has advanced since you
320 $ git fetch git://.... linus
321 $ LT=‘cat .git/FETCH_HEAD‘
324 Your work tree is still based on your HEAD ($JC), but you have some
325 edits since. Three-way merge makes sure that you have not added or
326 modified index entries since $JC, and if you haven’t, then does the
327 right thing. So with the following sequence:
329 $ git read-tree -m -u ‘git merge-base $JC $LT‘ $JC $LT
330 $ git merge-index git-merge-one-file -a
331 $ echo "Merge with Linus" | \
332 git commit-tree ‘git write-tree‘ -p $JC -p $LT
335 what you would commit is a pure merge between $JC and $LT without your
336 work-in-progress changes, and your work tree would be updated to the
339 However, if you have local changes in the working tree that would be
340 overwritten by this merge, _
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341 your changes from being lost.
343 In other words, there is no need to worry about what exists only in the
344 working tree. When you have local changes in a part of the project that
345 is not involved in the merge, your changes do not interfere with the
346 merge, and are kept intact. When they d
\bdo
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347 even start (_
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\be complains loudly and fails without modifying
348 anything). In such a case, you can simply continue doing what you were
349 in the middle of doing, and when your working tree is ready (i.e. you
350 have finished your work-in-progress), attempt the merge again.
352 S
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353 "Sparse checkout" allows to sparsely populate working directory. It
354 uses skip-worktree bit (see g
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\bx(1)) to tell Git whether a
355 file on working directory is worth looking at.
357 "git read-tree" and other merge-based commands ("git merge", "git
358 checkout"...) can help maintaining skip-worktree bitmap and working
359 directory update. $GIT_DIR/info/sparse-checkout is used to define the
360 skip-worktree reference bitmap. When "git read-tree" needs to update
361 working directory, it will reset skip-worktree bit in index based on
362 this file, which uses the same syntax as .gitignore files. If an entry
363 matches a pattern in this file, skip-worktree will be set on that
364 entry. Otherwise, skip-worktree will be unset.
366 Then it compares the new skip-worktree value with the previous one. If
367 skip-worktree turns from unset to set, it will add the corresponding
368 file back. If it turns from set to unset, that file will be removed.
370 While $GIT_DIR/info/sparse-checkout is usually used to specify what
371 files are in. You can also specify what files are _
\bn_
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\bt in, using negate
372 patterns. For example, to remove file "unwanted":
378 Another tricky thing is fully repopulating working directory when you
379 no longer want sparse checkout. You cannot just disable "sparse
380 checkout" because skip-worktree are still in the index and you working
381 directory is still sparsely populated. You should re-populate working
382 directory with the $GIT_DIR/info/sparse-checkout file content as
388 Then you can disable sparse checkout. Sparse checkout support in "git
389 read-tree" and similar commands is disabled by default. You need to
390 turn core.sparseCheckout on in order to have sparse checkout support.
392 S
\bSE
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\bE A
\bAL
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393 g
\bgi
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\b-w
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\be(1); g
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\bs(1); g
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\be(5)
395 A
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\bTH
\bHO
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\bR
396 Written by Linus Torvalds <t
\bto
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\bsd
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398 D
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399 Documentation by David Greaves, Junio C Hamano and the git-list
400 <g
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\br.
\b.k
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\b.o
\bor
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\bg[2]>.
403 Part of the g
\bgi
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\bt(1) suite
407 mailto:torvalds@osdl.org
409 2. git@vger.kernel.org
410 mailto:git@vger.kernel.org
414 Git 1.7.1.1.g16e90.d 04/30/2010 GIT-READ-TREE(1)