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20 .TH "GIT-READ-TREE" 1 "" "" ""
22 git-read-tree \- Reads tree information into the index
26 git\-read\-tree (<tree\-ish> | [[\-m | \-\-reset] [\-u | \-i]] <tree\-ish1> [<tree\-ish2> [<tree\-ish3>]])
31 Reads the tree information given by <tree\-ish> into the index, but does not actually update any of the files it "caches"\&. (see: \fBgit\-checkout\-index\fR(1))
34 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\&.
37 Trivial merges are done by git\-read\-tree itself\&. Only conflicting paths will be in unmerged state when git\-read\-tree returns\&.
43 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\&.
47 Same as \-m, except that unmerged entries are discarded instead of failing\&.
51 After a successful merge, update the files in the work tree with the result of the merge\&.
55 Usually a merge requires the index file as well as the files in the working tree are 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\&.
59 The id of the tree object(s) to be read/merged\&.
64 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\&.
66 .SS "Single Tree Merge"
69 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 matches 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)\&.
72 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\&.
75 This is used to avoid unnecessary false hits when git\-diff\-files is run after git\-read\-tree\&.
80 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)\&.
83 When two trees are specified, the user is telling git\-read\-tree the following:
87 The current index and work tree is derived from $H, but the user may have local changes in them since $H;
90 The user wants to fast\-forward to $M\&.
94 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:
98 \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
99 0 nothing nothing nothing (does not happen)
100 1 nothing nothing exists use M
101 2 nothing exists nothing remove path from index
102 3 nothing exists exists use M
107 \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
108 4 yes N/A N/A nothing nothing keep index
109 5 no N/A N/A nothing nothing keep index
113 6 yes N/A yes nothing exists keep index
114 7 no N/A yes nothing exists keep index
115 8 yes N/A no nothing exists fail
116 9 no N/A no nothing exists fail
120 10 yes yes N/A exists nothing remove path from index
121 11 no yes N/A exists nothing fail
122 12 yes no N/A exists nothing fail
123 13 no no N/A exists nothing fail
129 14 yes exists exists keep index
130 15 no exists exists keep index
134 clean I==H I==M (H!=M)
135 \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
136 16 yes no no exists exists fail
137 17 no no no exists exists fail
138 18 yes no yes exists exists keep index
139 19 no no yes exists exists keep index
140 20 yes yes no exists exists use M
141 21 no yes no exists exists fail
145 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\&.
148 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 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 output after two\-tree merge\&.
153 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\&.
156 However, when you do git\-read\-tree with three trees, the "stage" starts out at 1\&.
159 This means that you can do
162 $ git\-read\-tree \-m <tree1> <tree2> <tree3>
164 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"\&. 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>\&.
167 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":
171 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)
174 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)
177 stage 1 and stage 3 are the same and stage 2 is different take stage 2 (we did something while they did nothing)
181 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\&.
184 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 you are trying to merge (stage 2 and 3 respectively)\&.
187 The order of stages 1, 2 and 3 (hence the order of three <tree\-ish> command line arguments) are significant when you start a 3\-way merge with an index file that is already populated\&. Here is an outline of how the algorithm works:
191 if a file exists in identical format in all three trees, it will automatically collapse to "merged" state by git\-read\-tree\&.
194 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\&.
197 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 now the merge algorithm ends up being really simple:
202 you walk the index in order, and ignore all entries of stage 0, since they've already been done\&.
205 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\&.
208 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 \&.\&.
215 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\&.
218 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 files in your work tree, and you can even have files with changes unrecorded in the index file\&. It is further assumed that this state is "derived" from the stage 2 tree\&. The 3\-way merge refuses to run if it finds an entry in the original index file that does not match stage 2\&.
221 This is done to prevent you from losing your work\-in\-progress changes, and mixing your random changes in an unrelated merge commit\&. To illustrate, suppose you start from what has been commited last to your repository:
224 $ JC=`git\-rev\-parse \-\-verify "HEAD^0"`
225 $ git\-checkout\-index \-f \-u \-a $JC
227 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:
230 $ git\-fetch git://\&.\&.\&.\&. linus
231 $ LT=`cat \&.git/FETCH_HEAD`
233 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 index entries since $JC, and if you haven't, then does the right thing\&. So with the following sequence:
236 $ git\-read\-tree \-m \-u `git\-merge\-base $JC $LT` $JC $LT
237 $ git\-merge\-index git\-merge\-one\-file \-a
238 $ echo "Merge with Linus" | \\
239 git\-commit\-tree `git\-write\-tree` \-p $JC \-p $LT
241 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\&.
244 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\&.
247 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\&.
252 \fBgit\-write\-tree\fR(1); \fBgit\-ls\-files\fR(1)
257 Written by Linus Torvalds <torvalds@osdl\&.org>
262 Documentation by David Greaves, Junio C Hamano and the git\-list <git@vger\&.kernel\&.org>\&.
267 Part of the \fBgit\fR(7) suite
projects / git.git / blob