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 735 <body class="manpage">
 736 <div id="header">
 737 <h1>
 738 gitdiffcore(7) Manual Page
 739 </h1>
 740 <h2>NAME</h2>
 741 <div class="sectionbody">
 742 <p>gitdiffcore -
 743    Tweaking diff output
 744 </p>
 745 </div>
 746 </div>
 747 <div id="content">
 748 <div class="sect1">
 749 <h2 id="_synopsis">SYNOPSIS</h2>
 750 <div class="sectionbody">
 751 <div class="verseblock">
 752 <pre class="content"><em>git diff</em> *</pre>
 753 <div class="attribution">
 754 </div></div>
 755 </div>
 756 </div>
 757 <div class="sect1">
 758 <h2 id="_description">DESCRIPTION</h2>
 759 <div class="sectionbody">
 760 <div class="paragraph"><p>The diff commands <em>git diff-index</em>, <em>git diff-files</em>, and <em>git diff-tree</em>
 761 can be told to manipulate differences they find in
 762 unconventional ways before showing <em>diff</em> output.  The manipulation
 763 is collectively called "diffcore transformation".  This short note
 764 describes what they are and how to use them to produce <em>diff</em> output
 765 that is easier to understand than the conventional kind.</p></div>
 766 </div>
 767 </div>
 768 <div class="sect1">
 769 <h2 id="_the_chain_of_operation">The chain of operation</h2>
 770 <div class="sectionbody">
 771 <div class="paragraph"><p>The <em>git diff-&#42;</em> family works by first comparing two sets of
 772 files:</p></div>
 773 <div class="ulist"><ul>
 774 <li>
 775 <p>
 776 <em>git diff-index</em> compares contents of a "tree" object and the
 777    working directory (when <code>--cached</code> flag is not used) or a
 778    "tree" object and the index file (when <code>--cached</code> flag is
 779    used);
 780 </p>
 781 </li>
 782 <li>
 783 <p>
 784 <em>git diff-files</em> compares contents of the index file and the
 785    working directory;
 786 </p>
 787 </li>
 788 <li>
 789 <p>
 790 <em>git diff-tree</em> compares contents of two "tree" objects;
 791 </p>
 792 </li>
 793 </ul></div>
 794 <div class="paragraph"><p>In all of these cases, the commands themselves first optionally limit
 795 the two sets of files by any pathspecs given on their command-lines,
 796 and compare corresponding paths in the two resulting sets of files.</p></div>
 797 <div class="paragraph"><p>The pathspecs are used to limit the world diff operates in.  They remove
 798 the filepairs outside the specified sets of pathnames.  E.g. If the
 799 input set of filepairs included:</p></div>
 800 <div class="listingblock">
 801 <div class="content">
 802 <pre><code>:100644 100644 bcd1234... 0123456... M junkfile</code></pre>
 803 </div></div>
 804 <div class="paragraph"><p>but the command invocation was <code>git diff-files myfile</code>, then the
 805 junkfile entry would be removed from the list because only "myfile"
 806 is under consideration.</p></div>
 807 <div class="paragraph"><p>The result of comparison is passed from these commands to what is
 808 internally called "diffcore", in a format similar to what is output
 809 when the -p option is not used.  E.g.</p></div>
 810 <div class="listingblock">
 811 <div class="content">
 812 <pre><code>in-place edit  :100644 100644 bcd1234... 0123456... M file0
 813 create         :000000 100644 0000000... 1234567... A file4
 814 delete         :100644 000000 1234567... 0000000... D file5
 815 unmerged       :000000 000000 0000000... 0000000... U file6</code></pre>
 816 </div></div>
 817 <div class="paragraph"><p>The diffcore mechanism is fed a list of such comparison results
 818 (each of which is called "filepair", although at this point each
 819 of them talks about a single file), and transforms such a list
 820 into another list.  There are currently 5 such transformations:</p></div>
 821 <div class="ulist"><ul>
 822 <li>
 823 <p>
 824 diffcore-break
 825 </p>
 826 </li>
 827 <li>
 828 <p>
 829 diffcore-rename
 830 </p>
 831 </li>
 832 <li>
 833 <p>
 834 diffcore-merge-broken
 835 </p>
 836 </li>
 837 <li>
 838 <p>
 839 diffcore-pickaxe
 840 </p>
 841 </li>
 842 <li>
 843 <p>
 844 diffcore-order
 845 </p>
 846 </li>
 847 <li>
 848 <p>
 849 diffcore-rotate
 850 </p>
 851 </li>
 852 </ul></div>
 853 <div class="paragraph"><p>These are applied in sequence.  The set of filepairs <em>git diff-&#42;</em>
 854 commands find are used as the input to diffcore-break, and
 855 the output from diffcore-break is used as the input to the
 856 next transformation.  The final result is then passed to the
 857 output routine and generates either diff-raw format (see Output
 858 format sections of the manual for <em>git diff-&#42;</em> commands) or
 859 diff-patch format.</p></div>
 860 </div>
 861 </div>
 862 <div class="sect1">
 863 <h2 id="_diffcore_break_for_splitting_up_complete_rewrites">diffcore-break: For Splitting Up Complete Rewrites</h2>
 864 <div class="sectionbody">
 865 <div class="paragraph"><p>The second transformation in the chain is diffcore-break, and is
 866 controlled by the -B option to the <em>git diff-&#42;</em> commands.  This is
 867 used to detect a filepair that represents "complete rewrite" and
 868 break such filepair into two filepairs that represent delete and
 869 create.  E.g.  If the input contained this filepair:</p></div>
 870 <div class="listingblock">
 871 <div class="content">
 872 <pre><code>:100644 100644 bcd1234... 0123456... M file0</code></pre>
 873 </div></div>
 874 <div class="paragraph"><p>and if it detects that the file "file0" is completely rewritten,
 875 it changes it to:</p></div>
 876 <div class="listingblock">
 877 <div class="content">
 878 <pre><code>:100644 000000 bcd1234... 0000000... D file0
 879 :000000 100644 0000000... 0123456... A file0</code></pre>
 880 </div></div>
 881 <div class="paragraph"><p>For the purpose of breaking a filepair, diffcore-break examines
 882 the extent of changes between the contents of the files before
 883 and after modification (i.e. the contents that have "bcd1234&#8230;"
 884 and "0123456&#8230;" as their SHA-1 content ID, in the above
 885 example).  The amount of deletion of original contents and
 886 insertion of new material are added together, and if it exceeds
 887 the "break score", the filepair is broken into two.  The break
 888 score defaults to 50% of the size of the smaller of the original
 889 and the result (i.e. if the edit shrinks the file, the size of
 890 the result is used; if the edit lengthens the file, the size of
 891 the original is used), and can be customized by giving a number
 892 after "-B" option (e.g. "-B75" to tell it to use 75%).</p></div>
 893 </div>
 894 </div>
 895 <div class="sect1">
 896 <h2 id="_diffcore_rename_for_detecting_renames_and_copies">diffcore-rename: For Detecting Renames and Copies</h2>
 897 <div class="sectionbody">
 898 <div class="paragraph"><p>This transformation is used to detect renames and copies, and is
 899 controlled by the -M option (to detect renames) and the -C option
 900 (to detect copies as well) to the <em>git diff-&#42;</em> commands.  If the
 901 input contained these filepairs:</p></div>
 902 <div class="listingblock">
 903 <div class="content">
 904 <pre><code>:100644 000000 0123456... 0000000... D fileX
 905 :000000 100644 0000000... 0123456... A file0</code></pre>
 906 </div></div>
 907 <div class="paragraph"><p>and the contents of the deleted file fileX is similar enough to
 908 the contents of the created file file0, then rename detection
 909 merges these filepairs and creates:</p></div>
 910 <div class="listingblock">
 911 <div class="content">
 912 <pre><code>:100644 100644 0123456... 0123456... R100 fileX file0</code></pre>
 913 </div></div>
 914 <div class="paragraph"><p>When the "-C" option is used, the original contents of modified files,
 915 and deleted files (and also unmodified files, if the
 916 "--find-copies-harder" option is used) are considered as candidates
 917 of the source files in rename/copy operation.  If the input were like
 918 these filepairs, that talk about a modified file fileY and a newly
 919 created file file0:</p></div>
 920 <div class="listingblock">
 921 <div class="content">
 922 <pre><code>:100644 100644 0123456... 1234567... M fileY
 923 :000000 100644 0000000... bcd3456... A file0</code></pre>
 924 </div></div>
 925 <div class="paragraph"><p>the original contents of fileY and the resulting contents of
 926 file0 are compared, and if they are similar enough, they are
 927 changed to:</p></div>
 928 <div class="listingblock">
 929 <div class="content">
 930 <pre><code>:100644 100644 0123456... 1234567... M fileY
 931 :100644 100644 0123456... bcd3456... C100 fileY file0</code></pre>
 932 </div></div>
 933 <div class="paragraph"><p>In both rename and copy detection, the same "extent of changes"
 934 algorithm used in diffcore-break is used to determine if two
 935 files are "similar enough", and can be customized to use
 936 a similarity score different from the default of 50% by giving a
 937 number after the "-M" or "-C" option (e.g. "-M8" to tell it to use
 938 8/10 = 80%).</p></div>
 939 <div class="paragraph"><p>Note that when rename detection is on but both copy and break
 940 detection are off, rename detection adds a preliminary step that first
 941 checks if files are moved across directories while keeping their
 942 filename the same.  If there is a file added to a directory whose
 943 contents is sufficiently similar to a file with the same name that got
 944 deleted from a different directory, it will mark them as renames and
 945 exclude them from the later quadratic step (the one that pairwise
 946 compares all unmatched files to find the "best" matches, determined by
 947 the highest content similarity).  So, for example, if a deleted
 948 docs/ext.txt and an added docs/config/ext.txt are similar enough, they
 949 will be marked as a rename and prevent an added docs/ext.md that may
 950 be even more similar to the deleted docs/ext.txt from being considered
 951 as the rename destination in the later step.  For this reason, the
 952 preliminary "match same filename" step uses a bit higher threshold to
 953 mark a file pair as a rename and stop considering other candidates for
 954 better matches.  At most, one comparison is done per file in this
 955 preliminary pass; so if there are several remaining ext.txt files
 956 throughout the directory hierarchy after exact rename detection, this
 957 preliminary step may be skipped for those files.</p></div>
 958 <div class="paragraph"><p>Note.  When the "-C" option is used with <code>--find-copies-harder</code>
 959 option, <em>git diff-&#42;</em> commands feed unmodified filepairs to
 960 diffcore mechanism as well as modified ones.  This lets the copy
 961 detector consider unmodified files as copy source candidates at
 962 the expense of making it slower.  Without <code>--find-copies-harder</code>,
 963 <em>git diff-&#42;</em> commands can detect copies only if the file that was
 964 copied happened to have been modified in the same changeset.</p></div>
 965 </div>
 966 </div>
 967 <div class="sect1">
 968 <h2 id="_diffcore_merge_broken_for_putting_complete_rewrites_back_together">diffcore-merge-broken: For Putting Complete Rewrites Back Together</h2>
 969 <div class="sectionbody">
 970 <div class="paragraph"><p>This transformation is used to merge filepairs broken by
 971 diffcore-break, and not transformed into rename/copy by
 972 diffcore-rename, back into a single modification.  This always
 973 runs when diffcore-break is used.</p></div>
 974 <div class="paragraph"><p>For the purpose of merging broken filepairs back, it uses a
 975 different "extent of changes" computation from the ones used by
 976 diffcore-break and diffcore-rename.  It counts only the deletion
 977 from the original, and does not count insertion.  If you removed
 978 only 10 lines from a 100-line document, even if you added 910
 979 new lines to make a new 1000-line document, you did not do a
 980 complete rewrite.  diffcore-break breaks such a case in order to
 981 help diffcore-rename to consider such filepairs as candidate of
 982 rename/copy detection, but if filepairs broken that way were not
 983 matched with other filepairs to create rename/copy, then this
 984 transformation merges them back into the original
 985 "modification".</p></div>
 986 <div class="paragraph"><p>The "extent of changes" parameter can be tweaked from the
 987 default 80% (that is, unless more than 80% of the original
 988 material is deleted, the broken pairs are merged back into a
 989 single modification) by giving a second number to -B option,
 990 like these:</p></div>
 991 <div class="ulist"><ul>
 992 <li>
 993 <p>
 994 -B50/60 (give 50% "break score" to diffcore-break, use 60%
 995   for diffcore-merge-broken).
 996 </p>
 997 </li>
 998 <li>
 999 <p>
1000 -B/60 (the same as above, since diffcore-break defaults to 50%).
1001 </p>
1002 </li>
1003 </ul></div>
1004 <div class="paragraph"><p>Note that earlier implementation left a broken pair as a separate
1005 creation and deletion patches.  This was an unnecessary hack and
1006 the latest implementation always merges all the broken pairs
1007 back into modifications, but the resulting patch output is
1008 formatted differently for easier review in case of such
1009 a complete rewrite by showing the entire contents of old version
1010 prefixed with <em>-</em>, followed by the entire contents of new
1011 version prefixed with <em>+</em>.</p></div>
1012 </div>
1013 </div>
1014 <div class="sect1">
1015 <h2 id="_diffcore_pickaxe_for_detecting_addition_deletion_of_specified_string">diffcore-pickaxe: For Detecting Addition/Deletion of Specified String</h2>
1016 <div class="sectionbody">
1017 <div class="paragraph"><p>This transformation limits the set of filepairs to those that change
1018 specified strings between the preimage and the postimage in a certain
1019 way.  -S&lt;block of text&gt; and -G&lt;regular expression&gt; options are used to
1020 specify different ways these strings are sought.</p></div>
1021 <div class="paragraph"><p>"-S&lt;block of text&gt;" detects filepairs whose preimage and postimage
1022 have different number of occurrences of the specified block of text.
1023 By definition, it will not detect in-file moves.  Also, when a
1024 changeset moves a file wholesale without affecting the interesting
1025 string, diffcore-rename kicks in as usual, and <code>-S</code> omits the filepair
1026 (since the number of occurrences of that string didn&#8217;t change in that
1027 rename-detected filepair).  When used with <code>--pickaxe-regex</code>, treat
1028 the &lt;block of text&gt; as an extended POSIX regular expression to match,
1029 instead of a literal string.</p></div>
1030 <div class="paragraph"><p>"-G&lt;regular expression&gt;" (mnemonic: grep) detects filepairs whose
1031 textual diff has an added or a deleted line that matches the given
1032 regular expression.  This means that it will detect in-file (or what
1033 rename-detection considers the same file) moves, which is noise.  The
1034 implementation runs diff twice and greps, and this can be quite
1035 expensive.  To speed things up binary files without textconv filters
1036 will be ignored.</p></div>
1037 <div class="paragraph"><p>When <code>-S</code> or <code>-G</code> are used without <code>--pickaxe-all</code>, only filepairs
1038 that match their respective criterion are kept in the output.  When
1039 <code>--pickaxe-all</code> is used, if even one filepair matches their respective
1040 criterion in a changeset, the entire changeset is kept.  This behavior
1041 is designed to make reviewing changes in the context of the whole
1042 changeset easier.</p></div>
1043 </div>
1044 </div>
1045 <div class="sect1">
1046 <h2 id="_diffcore_order_for_sorting_the_output_based_on_filenames">diffcore-order: For Sorting the Output Based on Filenames</h2>
1047 <div class="sectionbody">
1048 <div class="paragraph"><p>This is used to reorder the filepairs according to the user&#8217;s
1049 (or project&#8217;s) taste, and is controlled by the -O option to the
1050 <em>git diff-&#42;</em> commands.</p></div>
1051 <div class="paragraph"><p>This takes a text file each of whose lines is a shell glob
1052 pattern.  Filepairs that match a glob pattern on an earlier line
1053 in the file are output before ones that match a later line, and
1054 filepairs that do not match any glob pattern are output last.</p></div>
1055 <div class="paragraph"><p>As an example, a typical orderfile for the core Git probably
1056 would look like this:</p></div>
1057 <div class="listingblock">
1058 <div class="content">
1059 <pre><code>README
1060 Makefile
1061 Documentation
1062 *.h
1063 *.c
1064 t</code></pre>
1065 </div></div>
1066 </div>
1067 </div>
1068 <div class="sect1">
1069 <h2 id="_diffcore_rotate_for_changing_at_which_path_output_starts">diffcore-rotate: For Changing At Which Path Output Starts</h2>
1070 <div class="sectionbody">
1071 <div class="paragraph"><p>This transformation takes one pathname, and rotates the set of
1072 filepairs so that the filepair for the given pathname comes first,
1073 optionally discarding the paths that come before it.  This is used
1074 to implement the <code>--skip-to</code> and the <code>--rotate-to</code> options.  It is
1075 an error when the specified pathname is not in the set of filepairs,
1076 but it is not useful to error out when used with "git log" family of
1077 commands, because it is unreasonable to expect that a given path
1078 would be modified by each and every commit shown by the "git log"
1079 command.  For this reason, when used with "git log", the filepair
1080 that sorts the same as, or the first one that sorts after, the given
1081 pathname is where the output starts.</p></div>
1082 <div class="paragraph"><p>Use of this transformation combined with diffcore-order will produce
1083 unexpected results, as the input to this transformation is likely
1084 not sorted when diffcore-order is in effect.</p></div>
1085 </div>
1086 </div>
1087 <div class="sect1">
1088 <h2 id="_see_also">SEE ALSO</h2>
1089 <div class="sectionbody">
1090 <div class="paragraph"><p><a href="git-diff.html">git-diff(1)</a>,
1091 <a href="git-diff-files.html">git-diff-files(1)</a>,
1092 <a href="git-diff-index.html">git-diff-index(1)</a>,
1093 <a href="git-diff-tree.html">git-diff-tree(1)</a>,
1094 <a href="git-format-patch.html">git-format-patch(1)</a>,
1095 <a href="git-log.html">git-log(1)</a>,
1096 <a href="gitglossary.html">gitglossary(7)</a>,
1097 <a href="user-manual.html">The Git User&#8217;s Manual</a></p></div>
1098 </div>
1099 </div>
1100 <div class="sect1">
1101 <h2 id="_git">GIT</h2>
1102 <div class="sectionbody">
1103 <div class="paragraph"><p>Part of the <a href="git.html">git(1)</a> suite</p></div>
1104 </div>
1105 </div>
1106 </div>
1107 <div id="footnotes"><hr /></div>
1108 <div id="footer">
1109 <div id="footer-text">
1110 Last updated
1111  2021-03-22 14:53:18 PDT
1112 </div>
1113 </div>
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