1GITDIFFCORE(7) Git Manual GITDIFFCORE(7)
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6 gitdiffcore - Tweaking diff output
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9 git diff *
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12 The diff commands git diff-index, git diff-files, and git diff-tree can
13 be told to manipulate differences they find in unconventional ways
14 before showing diff output. The manipulation is collectively called
15 "diffcore transformation". This short note describes what they are and
16 how to use them to produce diff output that is easier to understand
17 than the conventional kind.
18
20 The git diff-* family works by first comparing two sets of files:
21 · git diff-index compares contents of a "tree" object and the
23 working directory (when --cached flag is not used) or a "tree"
24 object and the index file (when --cached flag is used);
25 · git diff-files compares contents of the index file and the working
27 directory;
28 · git diff-tree compares contents of two "tree" objects;
30 In all of these cases, the commands themselves first optionally limit
32 the two sets of files by any pathspecs given on their command-lines,
33 and compare corresponding paths in the two resulting sets of files.
34 The pathspecs are used to limit the world diff operates in. They remove
36 the filepairs outside the specified sets of pathnames. E.g. If the
37 input set of filepairs included:
38 :100644 100644 bcd1234... 0123456... M junkfile
40 but the command invocation was git diff-files myfile, then the junkfile
43 entry would be removed from the list because only "myfile" is under
44 consideration.
45 The result of comparison is passed from these commands to what is
47 internally called "diffcore", in a format similar to what is output
48 when the -p option is not used. E.g.
49 in-place edit :100644 100644 bcd1234... 0123456... M file0
51 create :000000 100644 0000000... 1234567... A file4
52 delete :100644 000000 1234567... 0000000... D file5
53 unmerged :000000 000000 0000000... 0000000... U file6
54 The diffcore mechanism is fed a list of such comparison results (each
57 of which is called "filepair", although at this point each of them
58 talks about a single file), and transforms such a list into another
59 list. There are currently 5 such transformations:
60 · diffcore-break
62 · diffcore-rename
64 · diffcore-merge-broken
66 · diffcore-pickaxe
68 · diffcore-order
70 These are applied in sequence. The set of filepairs git diff-* commands
72 find are used as the input to diffcore-break, and the output from
73 diffcore-break is used as the input to the next transformation. The
74 final result is then passed to the output routine and generates either
75 diff-raw format (see Output format sections of the manual for git
76 diff-* commands) or diff-patch format.
77
79 The second transformation in the chain is diffcore-break, and is
80 controlled by the -B option to the git diff-* commands. This is used to
81 detect a filepair that represents "complete rewrite" and break such
82 filepair into two filepairs that represent delete and create. E.g. If
83 the input contained this filepair:
84 :100644 100644 bcd1234... 0123456... M file0
86 and if it detects that the file "file0" is completely rewritten, it
89 changes it to:
90 :100644 000000 bcd1234... 0000000... D file0
92 :000000 100644 0000000... 0123456... A file0
93 For the purpose of breaking a filepair, diffcore-break examines the
96 extent of changes between the contents of the files before and after
97 modification (i.e. the contents that have "bcd1234..." and "0123456..."
98 as their SHA1 content ID, in the above example). The amount of deletion
99 of original contents and insertion of new material are added together,
100 and if it exceeds the "break score", the filepair is broken into two.
101 The break score defaults to 50% of the size of the smaller of the
102 original and the result (i.e. if the edit shrinks the file, the size of
103 the result is used; if the edit lengthens the file, the size of the
104 original is used), and can be customized by giving a number after "-B"
105 option (e.g. "-B75" to tell it to use 75%).
106
108 This transformation is used to detect renames and copies, and is
109 controlled by the -M option (to detect renames) and the -C option (to
110 detect copies as well) to the git diff-* commands. If the input
111 contained these filepairs:
112 :100644 000000 0123456... 0000000... D fileX
114 :000000 100644 0000000... 0123456... A file0
115 and the contents of the deleted file fileX is similar enough to the
118 contents of the created file file0, then rename detection merges these
119 filepairs and creates:
120 :100644 100644 0123456... 0123456... R100 fileX file0
122 When the "-C" option is used, the original contents of modified files,
125 and deleted files (and also unmodified files, if the
126 "--find-copies-harder" option is used) are considered as candidates of
127 the source files in rename/copy operation. If the input were like these
128 filepairs, that talk about a modified file fileY and a newly created
129 file file0:
130 :100644 100644 0123456... 1234567... M fileY
132 :000000 100644 0000000... bcd3456... A file0
133 the original contents of fileY and the resulting contents of file0 are
136 compared, and if they are similar enough, they are changed to:
137 :100644 100644 0123456... 1234567... M fileY
139 :100644 100644 0123456... bcd3456... C100 fileY file0
140 In both rename and copy detection, the same "extent of changes"
143 algorithm used in diffcore-break is used to determine if two files are
144 "similar enough", and can be customized to use a similarity score
145 different from the default of 50% by giving a number after the "-M" or
146 "-C" option (e.g. "-M8" to tell it to use 8/10 = 80%).
147 Note. When the "-C" option is used with --find-copies-harder option,
149 git diff-* commands feed unmodified filepairs to diffcore mechanism as
150 well as modified ones. This lets the copy detector consider unmodified
151 files as copy source candidates at the expense of making it slower.
152 Without --find-copies-harder, git diff-* commands can detect copies
153 only if the file that was copied happened to have been modified in the
154 same changeset.
155
157 This transformation is used to merge filepairs broken by
158 diffcore-break, and not transformed into rename/copy by
159 diffcore-rename, back into a single modification. This always runs when
160 diffcore-break is used.
161 For the purpose of merging broken filepairs back, it uses a different
163 "extent of changes" computation from the ones used by diffcore-break
164 and diffcore-rename. It counts only the deletion from the original, and
165 does not count insertion. If you removed only 10 lines from a 100-line
166 document, even if you added 910 new lines to make a new 1000-line
167 document, you did not do a complete rewrite. diffcore-break breaks such
168 a case in order to help diffcore-rename to consider such filepairs as
169 candidate of rename/copy detection, but if filepairs broken that way
170 were not matched with other filepairs to create rename/copy, then this
171 transformation merges them back into the original "modification".
172 The "extent of changes" parameter can be tweaked from the default 80%
174 (that is, unless more than 80% of the original material is deleted, the
175 broken pairs are merged back into a single modification) by giving a
176 second number to -B option, like these:
177 · -B50/60 (give 50% "break score" to diffcore-break, use 60% for
179 diffcore-merge-broken).
180 · -B/60 (the same as above, since diffcore-break defaults to 50%).
182 Note that earlier implementation left a broken pair as a separate
184 creation and deletion patches. This was an unnecessary hack and the
185 latest implementation always merges all the broken pairs back into
186 modifications, but the resulting patch output is formatted differently
187 for easier review in case of such a complete rewrite by showing the
188 entire contents of old version prefixed with -, followed by the entire
189 contents of new version prefixed with +.
190
192 This transformation is used to find filepairs that represent changes
193 that touch a specified string, and is controlled by the -S option and
194 the --pickaxe-all option to the git diff-* commands.
195 When diffcore-pickaxe is in use, it checks if there are filepairs whose
197 "original" side has the specified string and whose "result" side does
198 not. Such a filepair represents "the string appeared in this
199 changeset". It also checks for the opposite case that loses the
200 specified string.
201 When --pickaxe-all is not in effect, diffcore-pickaxe leaves only such
203 filepairs that touch the specified string in its output. When
204 --pickaxe-all is used, diffcore-pickaxe leaves all filepairs intact if
205 there is such a filepair, or makes the output empty otherwise. The
206 latter behaviour is designed to make reviewing of the changes in the
207 context of the whole changeset easier.
208
210 This is used to reorder the filepairs according to the user’s (or
211 project’s) taste, and is controlled by the -O option to the git diff-*
212 commands.
213 This takes a text file each of whose lines is a shell glob pattern.
215 Filepairs that match a glob pattern on an earlier line in the file are
216 output before ones that match a later line, and filepairs that do not
217 match any glob pattern are output last.
218 As an example, a typical orderfile for the core git probably would look
220 like this:
221 README
223 Makefile
224 Documentation
225 *.h
226 *.c
227 t
228
231 git-diff(1), git-diff-files(1), git-diff-index(1), git-diff-tree(1),
232 git-format-patch(1), git-log(1), gitglossary(7), The Git User’s
233 Manual[1]
234
236 Part of the git(1) suite.
237
239 1. The Git User’s Manual
240 file:///usr/share/doc/git-1.7.1/user-manual.html
241Git 1.7.1 08/16/2017 GITDIFFCORE(7)