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    Command:

    gitdiffcore

    
    
    

    SYNOPSIS

           git diff *
    
    
    

    DESCRIPTION

           The diff commands git diff-index, git diff-files, and git diff-tree can
           be told to manipulate differences they find in unconventional ways
           before showing diff output. The manipulation is collectively called
           "diffcore transformation". This short note describes what they are and
           how to use them to produce diff output that is easier to understand
           than the conventional kind.
    
    
    

    THE CHAIN OF OPERATION

           The git diff-* family works by first comparing two sets of files:
    
           ?    git diff-index compares contents of a "tree" object and the
               working directory (when --cached flag is not used) or a "tree"
               object and the index file (when --cached flag is used);
    
           ?    git diff-files compares contents of the index file and the working
               directory;
    
           ?    git diff-tree compares contents of two "tree" objects;
    
           In all of these cases, the commands themselves first optionally limit
           the two sets of files by any pathspecs given on their command-lines,
           and compare corresponding paths in the two resulting sets of files.
    
           The pathspecs are used to limit the world diff operates in. They remove
           the filepairs outside the specified sets of pathnames. E.g. If the
           input set of filepairs included:
    
               :100644 100644 bcd1234... 0123456... M junkfile
    
           but the command invocation was git diff-files myfile, then the junkfile
           entry would be removed from the list because only "myfile" is under
           consideration.
    
           The result of comparison is passed from these commands to what is
           internally called "diffcore", in a format similar to what is output
           when the -p option is not used. E.g.
    
               in-place edit  :100644 100644 bcd1234... 0123456... M file0
               create         :000000 100644 0000000... 1234567... A file4
               delete         :100644 000000 1234567... 0000000... D file5
               unmerged       :000000 000000 0000000... 0000000... U file6
    
           The diffcore mechanism is fed a list of such comparison results (each
           of which is called "filepair", although at this point each of them
           talks about a single file), and transforms such a list into another
           list. There are currently 5 such transformations:
           final result is then passed to the output routine and generates either
           diff-raw format (see Output format sections of the manual for git
           diff-* commands) or diff-patch format.
    
    
    

    DIFFCORE-BREAK: FOR SPLITTING UP COMPLETE REWRITES""

           The second transformation in the chain is diffcore-break, and is
           controlled by the -B option to the git diff-* commands. This is used to
           detect a filepair that represents "complete rewrite" and break such
           filepair into two filepairs that represent delete and create. E.g. If
           the input contained this filepair:
    
               :100644 100644 bcd1234... 0123456... M file0
    
           and if it detects that the file "file0" is completely rewritten, it
           changes it to:
    
               :100644 000000 bcd1234... 0000000... D file0
               :000000 100644 0000000... 0123456... A file0
    
           For the purpose of breaking a filepair, diffcore-break examines the
           extent of changes between the contents of the files before and after
           modification (i.e. the contents that have "bcd1234..." and "0123456..."
           as their SHA1 content ID, in the above example). The amount of deletion
           of original contents and insertion of new material are added together,
           and if it exceeds the "break score", the filepair is broken into two.
           The break score defaults to 50% of the size of the smaller of the
           original and the result (i.e. if the edit shrinks the file, the size of
           the result is used; if the edit lengthens the file, the size of the
           original is used), and can be customized by giving a number after "-B"
           option (e.g. "-B75" to tell it to use 75%).
    
    
    

    DIFFCORE-RENAME: FOR DETECTION RENAMES AND COPIES

           This transformation is used to detect renames and copies, and is
           controlled by the -M option (to detect renames) and the -C option (to
           detect copies as well) to the git diff-* commands. If the input
           contained these filepairs:
    
               :100644 000000 0123456... 0000000... D fileX
               :000000 100644 0000000... 0123456... A file0
    
           and the contents of the deleted file fileX is similar enough to the
           contents of the created file file0, then rename detection merges these
           filepairs and creates:
    
               :100644 100644 0123456... 0123456... R100 fileX file0
    
           When the "-C" option is used, the original contents of modified files,
           and deleted files (and also unmodified files, if the
    
           In both rename and copy detection, the same "extent of changes"
           algorithm used in diffcore-break is used to determine if two files are
           "similar enough", and can be customized to use a similarity score
           different from the default of 50% by giving a number after the "-M" or
           "-C" option (e.g. "-M8" to tell it to use 8/10 = 80%).
    
           Note. When the "-C" option is used with --find-copies-harder option,
           git diff-* commands feed unmodified filepairs to diffcore mechanism as
           well as modified ones. This lets the copy detector consider unmodified
           files as copy source candidates at the expense of making it slower.
           Without --find-copies-harder, git diff-* commands can detect copies
           only if the file that was copied happened to have been modified in the
           same changeset.
    
    
    

    DIFFCORE-MERGE-BROKEN: FOR PUTTING COMPLETE REWRITES" BACK TOGETHER"

           This transformation is used to merge filepairs broken by
           diffcore-break, and not transformed into rename/copy by
           diffcore-rename, back into a single modification. This always runs when
           diffcore-break is used.
    
           For the purpose of merging broken filepairs back, it uses a different
           "extent of changes" computation from the ones used by diffcore-break
           and diffcore-rename. It counts only the deletion from the original, and
           does not count insertion. If you removed only 10 lines from a 100-line
           document, even if you added 910 new lines to make a new 1000-line
           document, you did not do a complete rewrite. diffcore-break breaks such
           a case in order to help diffcore-rename to consider such filepairs as
           candidate of rename/copy detection, but if filepairs broken that way
           were not matched with other filepairs to create rename/copy, then this
           transformation merges them back into the original "modification".
    
           The "extent of changes" parameter can be tweaked from the default 80%
           (that is, unless more than 80% of the original material is deleted, the
           broken pairs are merged back into a single modification) by giving a
           second number to -B option, like these:
    
           ?   -B50/60 (give 50% "break score" to diffcore-break, use 60% for
               diffcore-merge-broken).
    
           ?   -B/60 (the same as above, since diffcore-break defaults to 50%).
    
           Note that earlier implementation left a broken pair as a separate
           creation and deletion patches. This was an unnecessary hack and the
           latest implementation always merges all the broken pairs back into
           modifications, but the resulting patch output is formatted differently
           for easier review in case of such a complete rewrite by showing the
           entire contents of old version prefixed with -, followed by the entire
           contents of new version prefixed with +.
    
    
    

    DIFFCORE-PICKAXE: FOR DETECTING ADDITION/DELETION OF SPECIFIED STRING

           latter behaviour is designed to make reviewing of the changes in the
           context of the whole changeset easier.
    
    
    

    DIFFCORE-ORDER: FOR SORTING THE OUTPUT BASED ON FILENAMES

           This is used to reorder the filepairs according to the user's (or
           project's) taste, and is controlled by the -O option to the git diff-*
           commands.
    
           This takes a text file each of whose lines is a shell glob pattern.
           Filepairs that match a glob pattern on an earlier line in the file are
           output before ones that match a later line, and filepairs that do not
           match any glob pattern are output last.
    
           As an example, a typical orderfile for the core git probably would look
           like this:
    
               README
               Makefile
               Documentation
               *.h
               *.c
               t
    
    
    

    SEE ALSO

           git-diff(1), git-diff-files(1), git-diff-index(1), git-diff-tree(1),
           git-format-patch(1), git-log(1), gitglossary(7), The Git User's
           Manual[1]
    
    
    

    GIT

           Part of the git(1) suite.
    
    
    

    NOTES

            1. The Git User's Manual
               file:///usr/share/doc/git-1.7.1/user-manual.html
    
    
    

    Git 1.7.1 03/04/2013 GITDIFFCORE(7)

    
    
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