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1 | git-read-tree(1) |
2 | ================ | |
2cf565c5 DG |
3 | |
4 | NAME | |
5 | ---- | |
5f3aa197 | 6 | git-read-tree - Reads tree information into the index |
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7 | |
8 | ||
9 | SYNOPSIS | |
10 | -------- | |
f318dd22 | 11 | 'git-read-tree' (<tree-ish> | [-m [-u|-i]] <tree-ish1> [<tree-ish2> [<tree-ish3>]]) |
ccef66b5 | 12 | |
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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: |
215a7ad1 | 18 | git-checkout-index) |
2cf565c5 | 19 | |
5f3aa197 | 20 | Optionally, it can merge a tree into the index, perform a |
ccef66b5 JH |
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 | |
23 | the files in the work tree with the result of the merge. | |
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24 | |
25 | Trivial merges are done by "git-read-tree" itself. Only conflicting paths | |
26 | will be in unmerged state when "git-read-tree" returns. | |
27 | ||
28 | OPTIONS | |
29 | ------- | |
30 | -m:: | |
ccef66b5 JH |
31 | Perform a merge, not just a read. |
32 | ||
2db0bfbc NW |
33 | --reset:: |
34 | ||
35 | Same as -m except that unmerged entries will be silently ignored. | |
36 | ||
ccef66b5 JH |
37 | -u:: |
38 | After a successful merge, update the files in the work | |
39 | tree with the result of the merge. | |
2cf565c5 | 40 | |
f318dd22 JH |
41 | -i:: |
42 | Usually a merge requires the index file as well as the | |
43 | files in the working tree are up to date with the | |
44 | current head commit, in order not to lose local | |
45 | changes. This flag disables the check with the working | |
46 | tree and is meant to be used when creating a merge of | |
47 | trees that are not directly related to the current | |
48 | working tree status into a temporary index file. | |
49 | ||
50 | ||
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51 | <tree-ish#>:: |
52 | The id of the tree object(s) to be read/merged. | |
53 | ||
54 | ||
55 | Merging | |
56 | ------- | |
2c6e4771 | 57 | If '-m' is specified, "git-read-tree" can perform 3 kinds of |
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58 | merge, a single tree merge if only 1 tree is given, a |
59 | fast-forward merge with 2 trees, or a 3-way merge if 3 trees are | |
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60 | provided. |
61 | ||
ccef66b5 | 62 | |
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63 | Single Tree Merge |
64 | ~~~~~~~~~~~~~~~~~ | |
65 | If only 1 tree is specified, git-read-tree operates as if the user did not | |
5f3aa197 | 66 | specify '-m', except that if the original index has an entry for a |
2c6e4771 | 67 | given pathname, and the contents of the path matches with the tree |
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68 | being read, the stat info from the index is used. (In other words, the |
69 | index's stat()s take precedence over the merged tree's). | |
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70 | |
71 | That means that if you do a "git-read-tree -m <newtree>" followed by a | |
215a7ad1 | 72 | "git-checkout-index -f -u -a", the "git-checkout-index" only checks out |
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73 | the stuff that really changed. |
74 | ||
75 | This is used to avoid unnecessary false hits when "git-diff-files" is | |
76 | run after git-read-tree. | |
77 | ||
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78 | |
79 | Two Tree Merge | |
80 | ~~~~~~~~~~~~~~ | |
81 | ||
82 | Typically, this is invoked as "git-read-tree -m $H $M", where $H | |
83 | is the head commit of the current repository, and $M is the head | |
84 | of a foreign tree, which is simply ahead of $H (i.e. we are in a | |
85 | fast forward situation). | |
86 | ||
87 | When two trees are specified, the user is telling git-read-tree | |
88 | the following: | |
89 | ||
df8baa42 | 90 | 1. The current index and work tree is derived from $H, but |
c8596009 JH |
91 | the user may have local changes in them since $H; |
92 | ||
df8baa42 | 93 | 2. The user wants to fast-forward to $M. |
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94 | |
95 | In this case, the "git-read-tree -m $H $M" command makes sure | |
96 | that no local change is lost as the result of this "merge". | |
97 | Here are the "carry forward" rules: | |
98 | ||
99 | I (index) H M Result | |
100 | ------------------------------------------------------- | |
101 | 0 nothing nothing nothing (does not happen) | |
102 | 1 nothing nothing exists use M | |
5f3aa197 | 103 | 2 nothing exists nothing remove path from index |
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104 | 3 nothing exists exists use M |
105 | ||
106 | clean I==H I==M | |
107 | ------------------ | |
108 | 4 yes N/A N/A nothing nothing keep index | |
109 | 5 no N/A N/A nothing nothing keep index | |
110 | ||
111 | 6 yes N/A yes nothing exists keep index | |
112 | 7 no N/A yes nothing exists keep index | |
113 | 8 yes N/A no nothing exists fail | |
114 | 9 no N/A no nothing exists fail | |
115 | ||
5f3aa197 | 116 | 10 yes yes N/A exists nothing remove path from index |
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117 | 11 no yes N/A exists nothing fail |
118 | 12 yes no N/A exists nothing fail | |
119 | 13 no no N/A exists nothing fail | |
120 | ||
121 | clean (H=M) | |
122 | ------ | |
123 | 14 yes exists exists keep index | |
124 | 15 no exists exists keep index | |
125 | ||
126 | clean I==H I==M (H!=M) | |
127 | ------------------ | |
128 | 16 yes no no exists exists fail | |
129 | 17 no no no exists exists fail | |
130 | 18 yes no yes exists exists keep index | |
131 | 19 no no yes exists exists keep index | |
132 | 20 yes yes no exists exists use M | |
133 | 21 no yes no exists exists fail | |
134 | ||
5f3aa197 | 135 | In all "keep index" cases, the index entry stays as in the |
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136 | original index file. If the entry were not up to date, |
137 | git-read-tree keeps the copy in the work tree intact when | |
138 | operating under the -u flag. | |
139 | ||
140 | When this form of git-read-tree returns successfully, you can | |
141 | see what "local changes" you made are carried forward by running | |
215a7ad1 JH |
142 | "git-diff-index --cached $M". Note that this does not |
143 | necessarily match "git-diff-index --cached $H" would have | |
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144 | produced before such a two tree merge. This is because of cases |
145 | 18 and 19 --- if you already had the changes in $M (e.g. maybe | |
215a7ad1 | 146 | you picked it up via e-mail in a patch form), "git-diff-index |
c8596009 | 147 | --cached $H" would have told you about the change before this |
215a7ad1 | 148 | merge, but it would not show in "git-diff-index --cached $M" |
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149 | output after two-tree merge. |
150 | ||
151 | ||
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152 | 3-Way Merge |
153 | ~~~~~~~~~~~ | |
154 | Each "index" entry has two bits worth of "stage" state. stage 0 is the | |
155 | normal one, and is the only one you'd see in any kind of normal use. | |
156 | ||
157 | However, when you do "git-read-tree" with three trees, the "stage" | |
158 | starts out at 1. | |
159 | ||
160 | This means that you can do | |
161 | ||
162 | git-read-tree -m <tree1> <tree2> <tree3> | |
163 | ||
164 | and you will end up with an index with all of the <tree1> entries in | |
165 | "stage1", all of the <tree2> entries in "stage2" and all of the | |
166 | <tree3> entries in "stage3". | |
167 | ||
168 | Furthermore, "git-read-tree" has special-case logic that says: if you see | |
169 | a file that matches in all respects in the following states, it | |
170 | "collapses" back to "stage0": | |
171 | ||
172 | - stage 2 and 3 are the same; take one or the other (it makes no | |
173 | difference - the same work has been done on stage 2 and 3) | |
174 | ||
175 | - stage 1 and stage 2 are the same and stage 3 is different; take | |
176 | stage 3 (some work has been done on stage 3) | |
177 | ||
178 | - stage 1 and stage 3 are the same and stage 2 is different take | |
179 | stage 2 (some work has been done on stage 2) | |
180 | ||
181 | The "git-write-tree" command refuses to write a nonsensical tree, and it | |
182 | will complain about unmerged entries if it sees a single entry that is not | |
183 | stage 0. | |
184 | ||
185 | Ok, this all sounds like a collection of totally nonsensical rules, | |
186 | but it's actually exactly what you want in order to do a fast | |
187 | merge. The different stages represent the "result tree" (stage 0, aka | |
188 | "merged"), the original tree (stage 1, aka "orig"), and the two trees | |
189 | you are trying to merge (stage 2 and 3 respectively). | |
190 | ||
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191 | The order of stages 1, 2 and 3 (hence the order of three |
192 | <tree-ish> command line arguments) are significant when you | |
193 | start a 3-way merge with an index file that is already | |
194 | populated. Here is an outline of how the algorithm works: | |
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195 | |
196 | - if a file exists in identical format in all three trees, it will | |
ccef66b5 | 197 | automatically collapse to "merged" state by git-read-tree. |
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198 | |
199 | - a file that has _any_ difference what-so-ever in the three trees | |
2c6e4771 | 200 | will stay as separate entries in the index. It's up to "porcelain |
2cf565c5 | 201 | policy" to determine how to remove the non-0 stages, and insert a |
ccef66b5 | 202 | merged version. |
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203 | |
204 | - the index file saves and restores with all this information, so you | |
205 | can merge things incrementally, but as long as it has entries in | |
206 | stages 1/2/3 (ie "unmerged entries") you can't write the result. So | |
207 | now the merge algorithm ends up being really simple: | |
208 | ||
209 | * you walk the index in order, and ignore all entries of stage 0, | |
210 | since they've already been done. | |
211 | ||
212 | * if you find a "stage1", but no matching "stage2" or "stage3", you | |
213 | know it's been removed from both trees (it only existed in the | |
214 | original tree), and you remove that entry. | |
215 | ||
216 | * if you find a matching "stage2" and "stage3" tree, you remove one | |
217 | of them, and turn the other into a "stage0" entry. Remove any | |
218 | matching "stage1" entry if it exists too. .. all the normal | |
219 | trivial rules .. | |
220 | ||
215a7ad1 JH |
221 | You would normally use "git-merge-index" with supplied |
222 | "git-merge-one-file" to do this last step. The script | |
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223 | does not touch the files in the work tree, and the entire merge |
224 | happens in the index file. In other words, there is no need to | |
225 | worry about what is in the working directory, since it is never | |
226 | shown and never used. | |
227 | ||
228 | When you start a 3-way merge with an index file that is already | |
229 | populated, it is assumed that it represents the state of the | |
230 | files in your work tree, and you can even have files with | |
231 | changes unrecorded in the index file. It is further assumed | |
232 | that this state is "derived" from the stage 2 tree. The 3-way | |
233 | merge refuses to run if it finds an entry in the original index | |
234 | file that does not match stage 2. | |
235 | ||
236 | This is done to prevent you from losing your work-in-progress | |
237 | changes. To illustrate, suppose you start from what has been | |
238 | commited last to your repository: | |
239 | ||
cd0a781c | 240 | $ JC=`git-rev-parse --verify "HEAD^0"` |
215a7ad1 | 241 | $ git-checkout-index -f -u -a $JC |
ccef66b5 | 242 | |
215a7ad1 | 243 | You do random edits, without running git-update-index. And then |
ccef66b5 JH |
244 | you notice that the tip of your "upstream" tree has advanced |
245 | since you pulled from him: | |
246 | ||
215a7ad1 | 247 | $ git-fetch rsync://.... linus |
ccef66b5 JH |
248 | $ LT=`cat .git/MERGE_HEAD` |
249 | ||
250 | Your work tree is still based on your HEAD ($JC), but you have | |
251 | some edits since. Three-way merge makes sure that you have not | |
5f3aa197 | 252 | added or modified index entries since $JC, and if you haven't, |
ccef66b5 JH |
253 | then does the right thing. So with the following sequence: |
254 | ||
255 | $ git-read-tree -m -u `git-merge-base $JC $LT` $JC $LT | |
215a7ad1 | 256 | $ git-merge-index git-merge-one-file -a |
ccef66b5 JH |
257 | $ echo "Merge with Linus" | \ |
258 | git-commit-tree `git-write-tree` -p $JC -p $LT | |
259 | ||
260 | what you would commit is a pure merge between $JC and LT without | |
261 | your work-in-progress changes, and your work tree would be | |
262 | updated to the result of the merge. | |
263 | ||
2cf565c5 | 264 | |
c1bdacf9 DG |
265 | See Also |
266 | -------- | |
a7154e91 | 267 | gitlink:git-write-tree[1]; gitlink:git-ls-files[1] |
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268 | |
269 | ||
270 | Author | |
271 | ------ | |
272 | Written by Linus Torvalds <torvalds@osdl.org> | |
273 | ||
274 | Documentation | |
275 | -------------- | |
276 | Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>. | |
277 | ||
278 | GIT | |
279 | --- | |
a7154e91 | 280 | Part of the gitlink:git[7] suite |
2cf565c5 | 281 |