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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 | -------- | |
7791a1d9 | 11 | [verse] |
5a56da58 SB |
12 | 'git read-tree' [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] |
13 | [-u [--exclude-per-directory=<gitignore>] | -i]] | |
a5d07d0f | 14 | [--index-output=<file>] [--no-sparse-checkout] |
fb1bb965 | 15 | (--empty | <tree-ish1> [<tree-ish2> [<tree-ish3>]]) |
ccef66b5 | 16 | |
2cf565c5 DG |
17 | |
18 | DESCRIPTION | |
19 | ----------- | |
5f3aa197 | 20 | Reads the tree information given by <tree-ish> into the index, |
c1bdacf9 | 21 | but does not actually *update* any of the files it "caches". (see: |
5162e697 | 22 | linkgit:git-checkout-index[1]) |
2cf565c5 | 23 | |
5f3aa197 | 24 | Optionally, it can merge a tree into the index, perform a |
61f693bd JL |
25 | fast-forward (i.e. 2-way) merge, or a 3-way merge, with the `-m` |
26 | flag. When used with `-m`, the `-u` flag causes it to also update | |
ccef66b5 | 27 | the files in the work tree with the result of the merge. |
2cf565c5 | 28 | |
0b444cdb TR |
29 | Trivial merges are done by 'git read-tree' itself. Only conflicting paths |
30 | will be in unmerged state when 'git read-tree' returns. | |
2cf565c5 DG |
31 | |
32 | OPTIONS | |
33 | ------- | |
34 | -m:: | |
3f41f5a9 | 35 | Perform a merge, not just a read. The command will |
36 | refuse to run if your index file has unmerged entries, | |
37 | indicating that you have not finished previous merge you | |
38 | started. | |
ccef66b5 | 39 | |
2db0bfbc | 40 | --reset:: |
3f41f5a9 | 41 | Same as -m, except that unmerged entries are discarded |
42 | instead of failing. | |
2db0bfbc | 43 | |
ccef66b5 JH |
44 | -u:: |
45 | After a successful merge, update the files in the work | |
46 | tree with the result of the merge. | |
2cf565c5 | 47 | |
f318dd22 JH |
48 | -i:: |
49 | Usually a merge requires the index file as well as the | |
cc1a2b66 | 50 | files in the working tree to be up to date with the |
f318dd22 JH |
51 | current head commit, in order not to lose local |
52 | changes. This flag disables the check with the working | |
53 | tree and is meant to be used when creating a merge of | |
54 | trees that are not directly related to the current | |
55 | working tree status into a temporary index file. | |
56 | ||
ea5070c9 JL |
57 | -n:: |
58 | --dry-run:: | |
59 | Check if the command would error out, without updating the index | |
60 | nor the files in the working tree for real. | |
61 | ||
22e801f2 MV |
62 | -v:: |
63 | Show the progress of checking files out. | |
64 | ||
6da08783 | 65 | --trivial:: |
0b444cdb | 66 | Restrict three-way merge by 'git read-tree' to happen |
6da08783 JN |
67 | only if there is no file-level merging required, instead |
68 | of resolving merge for trivial cases and leaving | |
69 | conflicting files unresolved in the index. | |
70 | ||
afaa8d66 | 71 | --aggressive:: |
0b444cdb | 72 | Usually a three-way merge by 'git read-tree' resolves |
afaa8d66 | 73 | the merge for really trivial cases and leaves other |
cc1a2b66 | 74 | cases unresolved in the index, so that porcelains can |
afaa8d66 | 75 | implement different merge policies. This flag makes the |
cc1a2b66 | 76 | command resolve a few more cases internally: |
afaa8d66 JH |
77 | + |
78 | * when one side removes a path and the other side leaves the path | |
79 | unmodified. The resolution is to remove that path. | |
80 | * when both sides remove a path. The resolution is to remove that path. | |
cc1a2b66 | 81 | * when both sides add a path identically. The resolution |
afaa8d66 JH |
82 | is to add that path. |
83 | ||
f4c6f2d3 JH |
84 | --prefix=<prefix>/:: |
85 | Keep the current index contents, and read the contents | |
cc1a2b66 | 86 | of the named tree-ish under the directory at `<prefix>`. The |
f4c6f2d3 | 87 | original index file cannot have anything at the path |
cc1a2b66 | 88 | `<prefix>` itself, nor anything in the `<prefix>/` |
f4c6f2d3 JH |
89 | directory. Note that the `<prefix>/` value must end |
90 | with a slash. | |
91 | ||
22f741da JH |
92 | --exclude-per-directory=<gitignore>:: |
93 | When running the command with `-u` and `-m` options, the | |
94 | merge result may need to overwrite paths that are not | |
95 | tracked in the current branch. The command usually | |
96 | refuses to proceed with the merge to avoid losing such a | |
97 | path. However this safety valve sometimes gets in the | |
98 | way. For example, it often happens that the other | |
99 | branch added a file that used to be a generated file in | |
100 | your branch, and the safety valve triggers when you try | |
101 | to switch to that branch after you ran `make` but before | |
102 | running `make clean` to remove the generated file. This | |
103 | option tells the command to read per-directory exclude | |
104 | file (usually '.gitignore') and allows such an untracked | |
105 | but explicitly ignored file to be overwritten. | |
f4c6f2d3 | 106 | |
5e7f56ac JH |
107 | --index-output=<file>:: |
108 | Instead of writing the results out to `$GIT_INDEX_FILE`, | |
109 | write the resulting index in the named file. While the | |
110 | command is operating, the original index file is locked | |
111 | with the same mechanism as usual. The file must allow | |
112 | to be rename(2)ed into from a temporary file that is | |
113 | created next to the usual index file; typically this | |
114 | means it needs to be on the same filesystem as the index | |
115 | file itself, and you need write permission to the | |
116 | directories the index file and index output file are | |
117 | located in. | |
118 | ||
a5d07d0f NTND |
119 | --no-sparse-checkout:: |
120 | Disable sparse checkout support even if `core.sparseCheckout` | |
121 | is true. | |
122 | ||
fb1bb965 JK |
123 | --empty:: |
124 | Instead of reading tree object(s) into the index, just empty | |
125 | it. | |
126 | ||
2cf565c5 DG |
127 | <tree-ish#>:: |
128 | The id of the tree object(s) to be read/merged. | |
129 | ||
130 | ||
131 | Merging | |
132 | ------- | |
0b444cdb | 133 | If `-m` is specified, 'git read-tree' can perform 3 kinds of |
ccef66b5 JH |
134 | merge, a single tree merge if only 1 tree is given, a |
135 | fast-forward merge with 2 trees, or a 3-way merge if 3 trees are | |
2cf565c5 DG |
136 | provided. |
137 | ||
ccef66b5 | 138 | |
2cf565c5 DG |
139 | Single Tree Merge |
140 | ~~~~~~~~~~~~~~~~~ | |
0b444cdb | 141 | If only 1 tree is specified, 'git read-tree' operates as if the user did not |
61f693bd | 142 | specify `-m`, except that if the original index has an entry for a |
73252839 | 143 | given pathname, and the contents of the path match with the tree |
5f3aa197 LS |
144 | being read, the stat info from the index is used. (In other words, the |
145 | index's stat()s take precedence over the merged tree's). | |
2cf565c5 | 146 | |
b1889c36 | 147 | That means that if you do a `git read-tree -m <newtree>` followed by a |
0b444cdb | 148 | `git checkout-index -f -u -a`, the 'git checkout-index' only checks out |
2cf565c5 DG |
149 | the stuff that really changed. |
150 | ||
0b444cdb TR |
151 | This is used to avoid unnecessary false hits when 'git diff-files' is |
152 | run after 'git read-tree'. | |
2cf565c5 | 153 | |
c8596009 JH |
154 | |
155 | Two Tree Merge | |
156 | ~~~~~~~~~~~~~~ | |
157 | ||
b1889c36 | 158 | Typically, this is invoked as `git read-tree -m $H $M`, where $H |
c8596009 JH |
159 | is the head commit of the current repository, and $M is the head |
160 | of a foreign tree, which is simply ahead of $H (i.e. we are in a | |
a75d7b54 | 161 | fast-forward situation). |
c8596009 | 162 | |
0b444cdb | 163 | When two trees are specified, the user is telling 'git read-tree' |
c8596009 JH |
164 | the following: |
165 | ||
df8baa42 | 166 | 1. The current index and work tree is derived from $H, but |
73252839 | 167 | the user may have local changes in them since $H. |
c8596009 | 168 | |
df8baa42 | 169 | 2. The user wants to fast-forward to $M. |
c8596009 | 170 | |
b1889c36 | 171 | In this case, the `git read-tree -m $H $M` command makes sure |
c8596009 | 172 | that no local change is lost as the result of this "merge". |
73252839 MG |
173 | Here are the "carry forward" rules, where "I" denotes the index, |
174 | "clean" means that index and work tree coincide, and "exists"/"nothing" | |
175 | refer to the presence of a path in the specified commit: | |
c8596009 | 176 | |
73252839 | 177 | I H M Result |
c8596009 | 178 | ------------------------------------------------------- |
71928f7f MG |
179 | 0 nothing nothing nothing (does not happen) |
180 | 1 nothing nothing exists use M | |
181 | 2 nothing exists nothing remove path from index | |
73252839 | 182 | 3 nothing exists exists, use M if "initial checkout", |
55218834 | 183 | H == M keep index otherwise |
73252839 | 184 | exists, fail |
55218834 | 185 | H != M |
c8596009 JH |
186 | |
187 | clean I==H I==M | |
188 | ------------------ | |
71928f7f MG |
189 | 4 yes N/A N/A nothing nothing keep index |
190 | 5 no N/A N/A nothing nothing keep index | |
c8596009 | 191 | |
71928f7f MG |
192 | 6 yes N/A yes nothing exists keep index |
193 | 7 no N/A yes nothing exists keep index | |
194 | 8 yes N/A no nothing exists fail | |
195 | 9 no N/A no nothing exists fail | |
c8596009 | 196 | |
5f3aa197 | 197 | 10 yes yes N/A exists nothing remove path from index |
c8596009 JH |
198 | 11 no yes N/A exists nothing fail |
199 | 12 yes no N/A exists nothing fail | |
200 | 13 no no N/A exists nothing fail | |
201 | ||
73252839 | 202 | clean (H==M) |
c8596009 JH |
203 | ------ |
204 | 14 yes exists exists keep index | |
205 | 15 no exists exists keep index | |
206 | ||
207 | clean I==H I==M (H!=M) | |
208 | ------------------ | |
209 | 16 yes no no exists exists fail | |
210 | 17 no no no exists exists fail | |
211 | 18 yes no yes exists exists keep index | |
212 | 19 no no yes exists exists keep index | |
213 | 20 yes yes no exists exists use M | |
214 | 21 no yes no exists exists fail | |
215 | ||
5f3aa197 | 216 | In all "keep index" cases, the index entry stays as in the |
73252839 | 217 | original index file. If the entry is not up to date, |
0b444cdb | 218 | 'git read-tree' keeps the copy in the work tree intact when |
c8596009 JH |
219 | operating under the -u flag. |
220 | ||
0b444cdb | 221 | When this form of 'git read-tree' returns successfully, you can |
73252839 | 222 | see which of the "local changes" that you made were carried forward by running |
b1889c36 | 223 | `git diff-index --cached $M`. Note that this does not |
73252839 | 224 | necessarily match what `git diff-index --cached $H` would have |
c8596009 JH |
225 | produced before such a two tree merge. This is because of cases |
226 | 18 and 19 --- if you already had the changes in $M (e.g. maybe | |
b1889c36 | 227 | you picked it up via e-mail in a patch form), `git diff-index |
61f693bd | 228 | --cached $H` would have told you about the change before this |
b1889c36 | 229 | merge, but it would not show in `git diff-index --cached $M` |
73252839 | 230 | output after the two-tree merge. |
c8596009 | 231 | |
73252839 | 232 | Case 3 is slightly tricky and needs explanation. The result from this |
55218834 | 233 | rule logically should be to remove the path if the user staged the removal |
79fd4cc7 | 234 | of the path and then switching to a new branch. That however will prevent |
55218834 | 235 | the initial checkout from happening, so the rule is modified to use M (new |
73252839 | 236 | tree) only when the content of the index is empty. Otherwise the removal |
55218834 | 237 | of the path is kept as long as $H and $M are the same. |
c8596009 | 238 | |
2cf565c5 DG |
239 | 3-Way Merge |
240 | ~~~~~~~~~~~ | |
241 | Each "index" entry has two bits worth of "stage" state. stage 0 is the | |
242 | normal one, and is the only one you'd see in any kind of normal use. | |
243 | ||
0b444cdb | 244 | However, when you do 'git read-tree' with three trees, the "stage" |
2cf565c5 DG |
245 | starts out at 1. |
246 | ||
247 | This means that you can do | |
248 | ||
61f693bd | 249 | ---------------- |
b1889c36 | 250 | $ git read-tree -m <tree1> <tree2> <tree3> |
61f693bd | 251 | ---------------- |
2cf565c5 DG |
252 | |
253 | and you will end up with an index with all of the <tree1> entries in | |
254 | "stage1", all of the <tree2> entries in "stage2" and all of the | |
bb6d7b89 JH |
255 | <tree3> entries in "stage3". When performing a merge of another |
256 | branch into the current branch, we use the common ancestor tree | |
257 | as <tree1>, the current branch head as <tree2>, and the other | |
258 | branch head as <tree3>. | |
2cf565c5 | 259 | |
0b444cdb | 260 | Furthermore, 'git read-tree' has special-case logic that says: if you see |
2cf565c5 DG |
261 | a file that matches in all respects in the following states, it |
262 | "collapses" back to "stage0": | |
263 | ||
264 | - stage 2 and 3 are the same; take one or the other (it makes no | |
bb6d7b89 JH |
265 | difference - the same work has been done on our branch in |
266 | stage 2 and their branch in stage 3) | |
2cf565c5 DG |
267 | |
268 | - stage 1 and stage 2 are the same and stage 3 is different; take | |
bb6d7b89 JH |
269 | stage 3 (our branch in stage 2 did not do anything since the |
270 | ancestor in stage 1 while their branch in stage 3 worked on | |
271 | it) | |
2cf565c5 DG |
272 | |
273 | - stage 1 and stage 3 are the same and stage 2 is different take | |
bb6d7b89 | 274 | stage 2 (we did something while they did nothing) |
2cf565c5 | 275 | |
0b444cdb | 276 | The 'git write-tree' command refuses to write a nonsensical tree, and it |
2cf565c5 DG |
277 | will complain about unmerged entries if it sees a single entry that is not |
278 | stage 0. | |
279 | ||
abda1ef5 | 280 | OK, this all sounds like a collection of totally nonsensical rules, |
2cf565c5 DG |
281 | but it's actually exactly what you want in order to do a fast |
282 | merge. The different stages represent the "result tree" (stage 0, aka | |
283 | "merged"), the original tree (stage 1, aka "orig"), and the two trees | |
284 | you are trying to merge (stage 2 and 3 respectively). | |
285 | ||
ccef66b5 JH |
286 | The order of stages 1, 2 and 3 (hence the order of three |
287 | <tree-ish> command line arguments) are significant when you | |
288 | start a 3-way merge with an index file that is already | |
289 | populated. Here is an outline of how the algorithm works: | |
2cf565c5 DG |
290 | |
291 | - if a file exists in identical format in all three trees, it will | |
0b444cdb | 292 | automatically collapse to "merged" state by 'git read-tree'. |
2cf565c5 DG |
293 | |
294 | - a file that has _any_ difference what-so-ever in the three trees | |
2c6e4771 | 295 | will stay as separate entries in the index. It's up to "porcelain |
2cf565c5 | 296 | policy" to determine how to remove the non-0 stages, and insert a |
ccef66b5 | 297 | merged version. |
2cf565c5 DG |
298 | |
299 | - the index file saves and restores with all this information, so you | |
300 | can merge things incrementally, but as long as it has entries in | |
abda1ef5 | 301 | stages 1/2/3 (i.e., "unmerged entries") you can't write the result. So |
2cf565c5 DG |
302 | now the merge algorithm ends up being really simple: |
303 | ||
304 | * you walk the index in order, and ignore all entries of stage 0, | |
305 | since they've already been done. | |
306 | ||
307 | * if you find a "stage1", but no matching "stage2" or "stage3", you | |
308 | know it's been removed from both trees (it only existed in the | |
309 | original tree), and you remove that entry. | |
310 | ||
311 | * if you find a matching "stage2" and "stage3" tree, you remove one | |
312 | of them, and turn the other into a "stage0" entry. Remove any | |
313 | matching "stage1" entry if it exists too. .. all the normal | |
314 | trivial rules .. | |
315 | ||
0b444cdb TR |
316 | You would normally use 'git merge-index' with supplied |
317 | 'git merge-one-file' to do this last step. The script updates | |
bb6d7b89 JH |
318 | the files in the working tree as it merges each path and at the |
319 | end of a successful merge. | |
ccef66b5 JH |
320 | |
321 | When you start a 3-way merge with an index file that is already | |
322 | populated, it is assumed that it represents the state of the | |
323 | files in your work tree, and you can even have files with | |
324 | changes unrecorded in the index file. It is further assumed | |
325 | that this state is "derived" from the stage 2 tree. The 3-way | |
326 | merge refuses to run if it finds an entry in the original index | |
327 | file that does not match stage 2. | |
328 | ||
329 | This is done to prevent you from losing your work-in-progress | |
bb6d7b89 JH |
330 | changes, and mixing your random changes in an unrelated merge |
331 | commit. To illustrate, suppose you start from what has been | |
37425065 | 332 | committed last to your repository: |
ccef66b5 | 333 | |
61f693bd | 334 | ---------------- |
b1889c36 JN |
335 | $ JC=`git rev-parse --verify "HEAD^0"` |
336 | $ git checkout-index -f -u -a $JC | |
61f693bd | 337 | ---------------- |
ccef66b5 | 338 | |
0b444cdb | 339 | You do random edits, without running 'git update-index'. And then |
ccef66b5 JH |
340 | you notice that the tip of your "upstream" tree has advanced |
341 | since you pulled from him: | |
342 | ||
61f693bd | 343 | ---------------- |
b1889c36 | 344 | $ git fetch git://.... linus |
bb6d7b89 | 345 | $ LT=`cat .git/FETCH_HEAD` |
61f693bd | 346 | ---------------- |
ccef66b5 JH |
347 | |
348 | Your work tree is still based on your HEAD ($JC), but you have | |
349 | some edits since. Three-way merge makes sure that you have not | |
5f3aa197 | 350 | added or modified index entries since $JC, and if you haven't, |
ccef66b5 JH |
351 | then does the right thing. So with the following sequence: |
352 | ||
61f693bd | 353 | ---------------- |
b1889c36 JN |
354 | $ git read-tree -m -u `git merge-base $JC $LT` $JC $LT |
355 | $ git merge-index git-merge-one-file -a | |
61f693bd | 356 | $ echo "Merge with Linus" | \ |
b1889c36 | 357 | git commit-tree `git write-tree` -p $JC -p $LT |
61f693bd | 358 | ---------------- |
ccef66b5 | 359 | |
61f693bd | 360 | what you would commit is a pure merge between $JC and $LT without |
ccef66b5 JH |
361 | your work-in-progress changes, and your work tree would be |
362 | updated to the result of the merge. | |
363 | ||
bb6d7b89 | 364 | However, if you have local changes in the working tree that |
0b444cdb | 365 | would be overwritten by this merge, 'git read-tree' will refuse |
bb6d7b89 JH |
366 | to run to prevent your changes from being lost. |
367 | ||
368 | In other words, there is no need to worry about what exists only | |
369 | in the working tree. When you have local changes in a part of | |
370 | the project that is not involved in the merge, your changes do | |
371 | not interfere with the merge, and are kept intact. When they | |
0b444cdb | 372 | *do* interfere, the merge does not even start ('git read-tree' |
bb6d7b89 JH |
373 | complains loudly and fails without modifying anything). In such |
374 | a case, you can simply continue doing what you were in the | |
375 | middle of doing, and when your working tree is ready (i.e. you | |
376 | have finished your work-in-progress), attempt the merge again. | |
377 | ||
2cf565c5 | 378 | |
ed5336a7 NTND |
379 | Sparse checkout |
380 | --------------- | |
381 | ||
cc1a2b66 MG |
382 | "Sparse checkout" allows populating the working directory sparsely. |
383 | It uses the skip-worktree bit (see linkgit:git-update-index[1]) to tell | |
384 | Git whether a file in the working directory is worth looking at. | |
ed5336a7 | 385 | |
cc1a2b66 MG |
386 | 'git read-tree' and other merge-based commands ('git merge', 'git |
387 | checkout'...) can help maintaining the skip-worktree bitmap and working | |
ed5336a7 | 388 | directory update. `$GIT_DIR/info/sparse-checkout` is used to |
cc1a2b66 MG |
389 | define the skip-worktree reference bitmap. When 'git read-tree' needs |
390 | to update the working directory, it resets the skip-worktree bit in the index | |
ed5336a7 | 391 | based on this file, which uses the same syntax as .gitignore files. |
1f1f575e MG |
392 | If an entry matches a pattern in this file, skip-worktree will not be |
393 | set on that entry. Otherwise, skip-worktree will be set. | |
ed5336a7 NTND |
394 | |
395 | Then it compares the new skip-worktree value with the previous one. If | |
1f1f575e MG |
396 | skip-worktree turns from set to unset, it will add the corresponding |
397 | file back. If it turns from unset to set, that file will be removed. | |
ed5336a7 NTND |
398 | |
399 | While `$GIT_DIR/info/sparse-checkout` is usually used to specify what | |
cc1a2b66 MG |
400 | files are in, you can also specify what files are _not_ in, using |
401 | negate patterns. For example, to remove the file `unwanted`: | |
ed5336a7 NTND |
402 | |
403 | ---------------- | |
5e821231 | 404 | /* |
ed5336a7 NTND |
405 | !unwanted |
406 | ---------------- | |
407 | ||
cc1a2b66 | 408 | Another tricky thing is fully repopulating the working directory when you |
ed5336a7 | 409 | no longer want sparse checkout. You cannot just disable "sparse |
cc1a2b66 MG |
410 | checkout" because skip-worktree bits are still in the index and your working |
411 | directory is still sparsely populated. You should re-populate the working | |
ed5336a7 NTND |
412 | directory with the `$GIT_DIR/info/sparse-checkout` file content as |
413 | follows: | |
414 | ||
415 | ---------------- | |
5e821231 | 416 | /* |
ed5336a7 NTND |
417 | ---------------- |
418 | ||
cc1a2b66 MG |
419 | Then you can disable sparse checkout. Sparse checkout support in 'git |
420 | read-tree' and similar commands is disabled by default. You need to | |
08aefc9e NTND |
421 | turn `core.sparseCheckout` on in order to have sparse checkout |
422 | support. | |
ed5336a7 NTND |
423 | |
424 | ||
56ae8df5 | 425 | SEE ALSO |
c1bdacf9 | 426 | -------- |
5162e697 DM |
427 | linkgit:git-write-tree[1]; linkgit:git-ls-files[1]; |
428 | linkgit:gitignore[5] | |
2cf565c5 | 429 | |
2cf565c5 DG |
430 | GIT |
431 | --- | |
9e1f0a85 | 432 | Part of the linkgit:git[1] suite |