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2cf565c5 DG |
1 | git-read-tree(1) |
2 | ================ | |
2cf565c5 DG |
3 | |
4 | NAME | |
5 | ---- | |
5f3aa197 | 6 | git-read-tree - Reads tree information into the index |
2cf565c5 DG |
7 | |
8 | ||
9 | SYNOPSIS | |
10 | -------- | |
b1889c36 | 11 | 'git read-tree' (<tree-ish> | [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] [--exclude-per-directory=<gitignore>] [--index-output=<file>] <tree-ish1> [<tree-ish2> [<tree-ish3>]]) |
ccef66b5 | 12 | |
2cf565c5 DG |
13 | |
14 | DESCRIPTION | |
15 | ----------- | |
5f3aa197 | 16 | Reads the tree information given by <tree-ish> into the index, |
c1bdacf9 | 17 | but does not actually *update* any of the files it "caches". (see: |
5162e697 | 18 | linkgit:git-checkout-index[1]) |
2cf565c5 | 19 | |
5f3aa197 | 20 | Optionally, it can merge a tree into the index, perform a |
61f693bd JL |
21 | fast-forward (i.e. 2-way) merge, or a 3-way merge, with the `-m` |
22 | flag. When used with `-m`, the `-u` flag causes it to also update | |
ccef66b5 | 23 | the files in the work tree with the result of the merge. |
2cf565c5 | 24 | |
ba020ef5 JN |
25 | Trivial merges are done by 'git-read-tree' itself. Only conflicting paths |
26 | will be in unmerged state when 'git-read-tree' returns. | |
2cf565c5 DG |
27 | |
28 | OPTIONS | |
29 | ------- | |
30 | -m:: | |
3f41f5a9 | 31 | Perform a merge, not just a read. The command will |
32 | refuse to run if your index file has unmerged entries, | |
33 | indicating that you have not finished previous merge you | |
34 | started. | |
ccef66b5 | 35 | |
2db0bfbc | 36 | --reset:: |
3f41f5a9 | 37 | Same as -m, except that unmerged entries are discarded |
38 | instead of failing. | |
2db0bfbc | 39 | |
ccef66b5 JH |
40 | -u:: |
41 | After a successful merge, update the files in the work | |
42 | tree with the result of the merge. | |
2cf565c5 | 43 | |
f318dd22 JH |
44 | -i:: |
45 | Usually a merge requires the index file as well as the | |
46 | files in the working tree are up to date with the | |
47 | current head commit, in order not to lose local | |
48 | changes. This flag disables the check with the working | |
49 | tree and is meant to be used when creating a merge of | |
50 | trees that are not directly related to the current | |
51 | working tree status into a temporary index file. | |
52 | ||
22e801f2 MV |
53 | -v:: |
54 | Show the progress of checking files out. | |
55 | ||
6da08783 | 56 | --trivial:: |
ba020ef5 | 57 | Restrict three-way merge by 'git-read-tree' to happen |
6da08783 JN |
58 | only if there is no file-level merging required, instead |
59 | of resolving merge for trivial cases and leaving | |
60 | conflicting files unresolved in the index. | |
61 | ||
afaa8d66 | 62 | --aggressive:: |
ba020ef5 | 63 | Usually a three-way merge by 'git-read-tree' resolves |
afaa8d66 JH |
64 | the merge for really trivial cases and leaves other |
65 | cases unresolved in the index, so that Porcelains can | |
66 | implement different merge policies. This flag makes the | |
67 | command to resolve a few more cases internally: | |
68 | + | |
69 | * when one side removes a path and the other side leaves the path | |
70 | unmodified. The resolution is to remove that path. | |
71 | * when both sides remove a path. The resolution is to remove that path. | |
72 | * when both sides adds a path identically. The resolution | |
73 | is to add that path. | |
74 | ||
f4c6f2d3 JH |
75 | --prefix=<prefix>/:: |
76 | Keep the current index contents, and read the contents | |
77 | of named tree-ish under directory at `<prefix>`. The | |
78 | original index file cannot have anything at the path | |
79 | `<prefix>` itself, and have nothing in `<prefix>/` | |
80 | directory. Note that the `<prefix>/` value must end | |
81 | with a slash. | |
82 | ||
22f741da JH |
83 | --exclude-per-directory=<gitignore>:: |
84 | When running the command with `-u` and `-m` options, the | |
85 | merge result may need to overwrite paths that are not | |
86 | tracked in the current branch. The command usually | |
87 | refuses to proceed with the merge to avoid losing such a | |
88 | path. However this safety valve sometimes gets in the | |
89 | way. For example, it often happens that the other | |
90 | branch added a file that used to be a generated file in | |
91 | your branch, and the safety valve triggers when you try | |
92 | to switch to that branch after you ran `make` but before | |
93 | running `make clean` to remove the generated file. This | |
94 | option tells the command to read per-directory exclude | |
95 | file (usually '.gitignore') and allows such an untracked | |
96 | but explicitly ignored file to be overwritten. | |
f4c6f2d3 | 97 | |
5e7f56ac JH |
98 | --index-output=<file>:: |
99 | Instead of writing the results out to `$GIT_INDEX_FILE`, | |
100 | write the resulting index in the named file. While the | |
101 | command is operating, the original index file is locked | |
102 | with the same mechanism as usual. The file must allow | |
103 | to be rename(2)ed into from a temporary file that is | |
104 | created next to the usual index file; typically this | |
105 | means it needs to be on the same filesystem as the index | |
106 | file itself, and you need write permission to the | |
107 | directories the index file and index output file are | |
108 | located in. | |
109 | ||
2cf565c5 DG |
110 | <tree-ish#>:: |
111 | The id of the tree object(s) to be read/merged. | |
112 | ||
113 | ||
114 | Merging | |
115 | ------- | |
ba020ef5 | 116 | If `-m` is specified, 'git-read-tree' can perform 3 kinds of |
ccef66b5 JH |
117 | merge, a single tree merge if only 1 tree is given, a |
118 | fast-forward merge with 2 trees, or a 3-way merge if 3 trees are | |
2cf565c5 DG |
119 | provided. |
120 | ||
ccef66b5 | 121 | |
2cf565c5 DG |
122 | Single Tree Merge |
123 | ~~~~~~~~~~~~~~~~~ | |
ba020ef5 | 124 | If only 1 tree is specified, 'git-read-tree' operates as if the user did not |
61f693bd | 125 | specify `-m`, except that if the original index has an entry for a |
2c6e4771 | 126 | given pathname, and the contents of the path matches with the tree |
5f3aa197 LS |
127 | being read, the stat info from the index is used. (In other words, the |
128 | index's stat()s take precedence over the merged tree's). | |
2cf565c5 | 129 | |
b1889c36 | 130 | That means that if you do a `git read-tree -m <newtree>` followed by a |
ba020ef5 | 131 | `git checkout-index -f -u -a`, the 'git-checkout-index' only checks out |
2cf565c5 DG |
132 | the stuff that really changed. |
133 | ||
ba020ef5 JN |
134 | This is used to avoid unnecessary false hits when 'git-diff-files' is |
135 | run after 'git-read-tree'. | |
2cf565c5 | 136 | |
c8596009 JH |
137 | |
138 | Two Tree Merge | |
139 | ~~~~~~~~~~~~~~ | |
140 | ||
b1889c36 | 141 | Typically, this is invoked as `git read-tree -m $H $M`, where $H |
c8596009 JH |
142 | is the head commit of the current repository, and $M is the head |
143 | of a foreign tree, which is simply ahead of $H (i.e. we are in a | |
144 | fast forward situation). | |
145 | ||
ba020ef5 | 146 | When two trees are specified, the user is telling 'git-read-tree' |
c8596009 JH |
147 | the following: |
148 | ||
df8baa42 | 149 | 1. The current index and work tree is derived from $H, but |
c8596009 JH |
150 | the user may have local changes in them since $H; |
151 | ||
df8baa42 | 152 | 2. The user wants to fast-forward to $M. |
c8596009 | 153 | |
b1889c36 | 154 | In this case, the `git read-tree -m $H $M` command makes sure |
c8596009 JH |
155 | that no local change is lost as the result of this "merge". |
156 | Here are the "carry forward" rules: | |
157 | ||
158 | I (index) H M Result | |
159 | ------------------------------------------------------- | |
160 | 0 nothing nothing nothing (does not happen) | |
161 | 1 nothing nothing exists use M | |
5f3aa197 | 162 | 2 nothing exists nothing remove path from index |
55218834 JH |
163 | 3 nothing exists exists, use M if "initial checkout" |
164 | H == M keep index otherwise | |
165 | exists fail | |
166 | H != M | |
c8596009 JH |
167 | |
168 | clean I==H I==M | |
169 | ------------------ | |
170 | 4 yes N/A N/A nothing nothing keep index | |
171 | 5 no N/A N/A nothing nothing keep index | |
172 | ||
173 | 6 yes N/A yes nothing exists keep index | |
174 | 7 no N/A yes nothing exists keep index | |
175 | 8 yes N/A no nothing exists fail | |
176 | 9 no N/A no nothing exists fail | |
177 | ||
5f3aa197 | 178 | 10 yes yes N/A exists nothing remove path from index |
c8596009 JH |
179 | 11 no yes N/A exists nothing fail |
180 | 12 yes no N/A exists nothing fail | |
181 | 13 no no N/A exists nothing fail | |
182 | ||
183 | clean (H=M) | |
184 | ------ | |
185 | 14 yes exists exists keep index | |
186 | 15 no exists exists keep index | |
187 | ||
188 | clean I==H I==M (H!=M) | |
189 | ------------------ | |
190 | 16 yes no no exists exists fail | |
191 | 17 no no no exists exists fail | |
192 | 18 yes no yes exists exists keep index | |
193 | 19 no no yes exists exists keep index | |
194 | 20 yes yes no exists exists use M | |
195 | 21 no yes no exists exists fail | |
196 | ||
5f3aa197 | 197 | In all "keep index" cases, the index entry stays as in the |
c8596009 | 198 | original index file. If the entry were not up to date, |
ba020ef5 | 199 | 'git-read-tree' keeps the copy in the work tree intact when |
c8596009 JH |
200 | operating under the -u flag. |
201 | ||
ba020ef5 | 202 | When this form of 'git-read-tree' returns successfully, you can |
c8596009 | 203 | see what "local changes" you made are carried forward by running |
b1889c36 JN |
204 | `git diff-index --cached $M`. Note that this does not |
205 | necessarily match `git diff-index --cached $H` would have | |
c8596009 JH |
206 | produced before such a two tree merge. This is because of cases |
207 | 18 and 19 --- if you already had the changes in $M (e.g. maybe | |
b1889c36 | 208 | you picked it up via e-mail in a patch form), `git diff-index |
61f693bd | 209 | --cached $H` would have told you about the change before this |
b1889c36 | 210 | merge, but it would not show in `git diff-index --cached $M` |
c8596009 JH |
211 | output after two-tree merge. |
212 | ||
55218834 JH |
213 | Case #3 is slightly tricky and needs explanation. The result from this |
214 | rule logically should be to remove the path if the user staged the removal | |
79fd4cc7 | 215 | of the path and then switching to a new branch. That however will prevent |
55218834 JH |
216 | the initial checkout from happening, so the rule is modified to use M (new |
217 | tree) only when the contents of the index is empty. Otherwise the removal | |
218 | of the path is kept as long as $H and $M are the same. | |
c8596009 | 219 | |
2cf565c5 DG |
220 | 3-Way Merge |
221 | ~~~~~~~~~~~ | |
222 | Each "index" entry has two bits worth of "stage" state. stage 0 is the | |
223 | normal one, and is the only one you'd see in any kind of normal use. | |
224 | ||
ba020ef5 | 225 | However, when you do 'git-read-tree' with three trees, the "stage" |
2cf565c5 DG |
226 | starts out at 1. |
227 | ||
228 | This means that you can do | |
229 | ||
61f693bd | 230 | ---------------- |
b1889c36 | 231 | $ git read-tree -m <tree1> <tree2> <tree3> |
61f693bd | 232 | ---------------- |
2cf565c5 DG |
233 | |
234 | and you will end up with an index with all of the <tree1> entries in | |
235 | "stage1", all of the <tree2> entries in "stage2" and all of the | |
bb6d7b89 JH |
236 | <tree3> entries in "stage3". When performing a merge of another |
237 | branch into the current branch, we use the common ancestor tree | |
238 | as <tree1>, the current branch head as <tree2>, and the other | |
239 | branch head as <tree3>. | |
2cf565c5 | 240 | |
ba020ef5 | 241 | Furthermore, 'git-read-tree' has special-case logic that says: if you see |
2cf565c5 DG |
242 | a file that matches in all respects in the following states, it |
243 | "collapses" back to "stage0": | |
244 | ||
245 | - stage 2 and 3 are the same; take one or the other (it makes no | |
bb6d7b89 JH |
246 | difference - the same work has been done on our branch in |
247 | stage 2 and their branch in stage 3) | |
2cf565c5 DG |
248 | |
249 | - stage 1 and stage 2 are the same and stage 3 is different; take | |
bb6d7b89 JH |
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 | |
252 | it) | |
2cf565c5 DG |
253 | |
254 | - stage 1 and stage 3 are the same and stage 2 is different take | |
bb6d7b89 | 255 | stage 2 (we did something while they did nothing) |
2cf565c5 | 256 | |
ba020ef5 | 257 | The 'git-write-tree' command refuses to write a nonsensical tree, and it |
2cf565c5 DG |
258 | will complain about unmerged entries if it sees a single entry that is not |
259 | stage 0. | |
260 | ||
abda1ef5 | 261 | OK, this all sounds like a collection of totally nonsensical rules, |
2cf565c5 DG |
262 | but it's actually exactly what you want in order to do a fast |
263 | merge. The different stages represent the "result tree" (stage 0, aka | |
264 | "merged"), the original tree (stage 1, aka "orig"), and the two trees | |
265 | you are trying to merge (stage 2 and 3 respectively). | |
266 | ||
ccef66b5 JH |
267 | The order of stages 1, 2 and 3 (hence the order of three |
268 | <tree-ish> command line arguments) are significant when you | |
269 | start a 3-way merge with an index file that is already | |
270 | populated. Here is an outline of how the algorithm works: | |
2cf565c5 DG |
271 | |
272 | - if a file exists in identical format in all three trees, it will | |
ba020ef5 | 273 | automatically collapse to "merged" state by 'git-read-tree'. |
2cf565c5 DG |
274 | |
275 | - a file that has _any_ difference what-so-ever in the three trees | |
2c6e4771 | 276 | will stay as separate entries in the index. It's up to "porcelain |
2cf565c5 | 277 | policy" to determine how to remove the non-0 stages, and insert a |
ccef66b5 | 278 | merged version. |
2cf565c5 DG |
279 | |
280 | - the index file saves and restores with all this information, so you | |
281 | can merge things incrementally, but as long as it has entries in | |
abda1ef5 | 282 | stages 1/2/3 (i.e., "unmerged entries") you can't write the result. So |
2cf565c5 DG |
283 | now the merge algorithm ends up being really simple: |
284 | ||
285 | * you walk the index in order, and ignore all entries of stage 0, | |
286 | since they've already been done. | |
287 | ||
288 | * if you find a "stage1", but no matching "stage2" or "stage3", you | |
289 | know it's been removed from both trees (it only existed in the | |
290 | original tree), and you remove that entry. | |
291 | ||
292 | * if you find a matching "stage2" and "stage3" tree, you remove one | |
293 | of them, and turn the other into a "stage0" entry. Remove any | |
294 | matching "stage1" entry if it exists too. .. all the normal | |
295 | trivial rules .. | |
296 | ||
ba020ef5 JN |
297 | You would normally use 'git-merge-index' with supplied |
298 | 'git-merge-one-file' to do this last step. The script updates | |
bb6d7b89 JH |
299 | the files in the working tree as it merges each path and at the |
300 | end of a successful merge. | |
ccef66b5 JH |
301 | |
302 | When you start a 3-way merge with an index file that is already | |
303 | populated, it is assumed that it represents the state of the | |
304 | files in your work tree, and you can even have files with | |
305 | changes unrecorded in the index file. It is further assumed | |
306 | that this state is "derived" from the stage 2 tree. The 3-way | |
307 | merge refuses to run if it finds an entry in the original index | |
308 | file that does not match stage 2. | |
309 | ||
310 | This is done to prevent you from losing your work-in-progress | |
bb6d7b89 JH |
311 | changes, and mixing your random changes in an unrelated merge |
312 | commit. To illustrate, suppose you start from what has been | |
37425065 | 313 | committed last to your repository: |
ccef66b5 | 314 | |
61f693bd | 315 | ---------------- |
b1889c36 JN |
316 | $ JC=`git rev-parse --verify "HEAD^0"` |
317 | $ git checkout-index -f -u -a $JC | |
61f693bd | 318 | ---------------- |
ccef66b5 | 319 | |
ba020ef5 | 320 | You do random edits, without running 'git-update-index'. And then |
ccef66b5 JH |
321 | you notice that the tip of your "upstream" tree has advanced |
322 | since you pulled from him: | |
323 | ||
61f693bd | 324 | ---------------- |
b1889c36 | 325 | $ git fetch git://.... linus |
bb6d7b89 | 326 | $ LT=`cat .git/FETCH_HEAD` |
61f693bd | 327 | ---------------- |
ccef66b5 JH |
328 | |
329 | Your work tree is still based on your HEAD ($JC), but you have | |
330 | some edits since. Three-way merge makes sure that you have not | |
5f3aa197 | 331 | added or modified index entries since $JC, and if you haven't, |
ccef66b5 JH |
332 | then does the right thing. So with the following sequence: |
333 | ||
61f693bd | 334 | ---------------- |
b1889c36 JN |
335 | $ git read-tree -m -u `git merge-base $JC $LT` $JC $LT |
336 | $ git merge-index git-merge-one-file -a | |
61f693bd | 337 | $ echo "Merge with Linus" | \ |
b1889c36 | 338 | git commit-tree `git write-tree` -p $JC -p $LT |
61f693bd | 339 | ---------------- |
ccef66b5 | 340 | |
61f693bd | 341 | what you would commit is a pure merge between $JC and $LT without |
ccef66b5 JH |
342 | your work-in-progress changes, and your work tree would be |
343 | updated to the result of the merge. | |
344 | ||
bb6d7b89 | 345 | However, if you have local changes in the working tree that |
ba020ef5 | 346 | would be overwritten by this merge, 'git-read-tree' will refuse |
bb6d7b89 JH |
347 | to run to prevent your changes from being lost. |
348 | ||
349 | In other words, there is no need to worry about what exists only | |
350 | in the working tree. When you have local changes in a part of | |
351 | the project that is not involved in the merge, your changes do | |
352 | not interfere with the merge, and are kept intact. When they | |
ba020ef5 | 353 | *do* interfere, the merge does not even start ('git-read-tree' |
bb6d7b89 JH |
354 | complains loudly and fails without modifying anything). In such |
355 | a case, you can simply continue doing what you were in the | |
356 | middle of doing, and when your working tree is ready (i.e. you | |
357 | have finished your work-in-progress), attempt the merge again. | |
358 | ||
2cf565c5 | 359 | |
56ae8df5 | 360 | SEE ALSO |
c1bdacf9 | 361 | -------- |
5162e697 DM |
362 | linkgit:git-write-tree[1]; linkgit:git-ls-files[1]; |
363 | linkgit:gitignore[5] | |
2cf565c5 DG |
364 | |
365 | ||
366 | Author | |
367 | ------ | |
368 | Written by Linus Torvalds <torvalds@osdl.org> | |
369 | ||
370 | Documentation | |
371 | -------------- | |
372 | Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>. | |
373 | ||
374 | GIT | |
375 | --- | |
9e1f0a85 | 376 | Part of the linkgit:git[1] suite |