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<body class="article">
<div id="header">
<h1>Git index format</h1>
</div>
<div id="content">
<div class="sect1">
<h2 id="_the_git_index_file_has_the_following_format">The Git index file has the following format</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre><code>All binary numbers are in network byte order. Version 2 is described
here unless stated otherwise.</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
A 12-byte header consisting of
</p>
<div class="literalblock">
<div class="content">
<pre><code>4-byte signature:
  The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>4-byte version number:
  The current supported versions are 2, 3 and 4.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit number of index entries.</code></pre>
</div></div>
</li>
<li>
<p>
A number of sorted index entries (see below).
</p>
</li>
<li>
<p>
Extensions
</p>
<div class="literalblock">
<div class="content">
<pre><code>Extensions are identified by signature. Optional extensions can
be ignored if Git does not understand them.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>Git currently supports cached tree and resolve undo extensions.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>4-byte extension signature. If the first byte is 'A'..'Z' the
extension is optional and can be ignored.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit size of the extension</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>Extension data</code></pre>
</div></div>
</li>
<li>
<p>
160-bit SHA-1 over the content of the index file before this
     checksum.
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_index_entry">Index entry</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre><code>Index entries are sorted in ascending order on the name field,
interpreted as a string of unsigned bytes (i.e. memcmp() order, no
localization, no special casing of directory separator '/'). Entries
with the same name are sorted by their stage field.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit ctime seconds, the last time a file's metadata changed
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit ctime nanosecond fractions
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit mtime seconds, the last time a file's data changed
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit mtime nanosecond fractions
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit dev
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit ino
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit mode, split into (high to low bits)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>4-bit object type
  valid values in binary are 1000 (regular file), 1010 (symbolic link)
  and 1110 (gitlink)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>3-bit unused</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>9-bit unix permission. Only 0755 and 0644 are valid for regular files.
Symbolic links and gitlinks have value 0 in this field.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit uid
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit gid
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit file size
  This is the on-disk size from stat(2), truncated to 32-bit.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>160-bit SHA-1 for the represented object</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>A 16-bit 'flags' field split into (high to low bits)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit assume-valid flag</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit extended flag (must be zero in version 2)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>2-bit stage (during merge)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
is stored in this field.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>(Version 3 or later) A 16-bit field, only applicable if the
"extended flag" above is 1, split into (high to low bits).</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit reserved for future</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit skip-worktree flag (used by sparse checkout)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit intent-to-add flag (used by "git add -N")</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>13-bit unused, must be zero</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>Entry path name (variable length) relative to top level directory
  (without leading slash). '/' is used as path separator. The special
  path components ".", ".." and ".git" (without quotes) are disallowed.
  Trailing slash is also disallowed.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The exact encoding is undefined, but the '.' and '/' characters
are encoded in 7-bit ASCII and the encoding cannot contain a NUL
byte (iow, this is a UNIX pathname).</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>(Version 4) In version 4, the entry path name is prefix-compressed
  relative to the path name for the previous entry (the very first
  entry is encoded as if the path name for the previous entry is an
  empty string).  At the beginning of an entry, an integer N in the
  variable width encoding (the same encoding as the offset is encoded
  for OFS_DELTA pack entries; see pack-format.txt) is stored, followed
  by a NUL-terminated string S.  Removing N bytes from the end of the
  path name for the previous entry, and replacing it with the string S
  yields the path name for this entry.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
while keeping the name NUL-terminated.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>(Version 4) In version 4, the padding after the pathname does not
exist.</code></pre>
</div></div>
</div>
</div>
<div class="sect1">
<h2 id="_extensions">Extensions</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_cached_tree">Cached tree</h3>
<div class="literalblock">
<div class="content">
<pre><code>Cached tree extension contains pre-computed hashes for trees that can
be derived from the index. It helps speed up tree object generation
from index for a new commit.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>When a path is updated in index, the path must be invalidated and
removed from tree cache.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The signature for this extension is { 'T', 'R', 'E', 'E' }.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>A series of entries fill the entire extension; each of which
consists of:</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
NUL-terminated path component (relative to its parent directory);
</p>
</li>
<li>
<p>
ASCII decimal number of entries in the index that is covered by the
    tree this entry represents (entry_count);
</p>
</li>
<li>
<p>
A space (ASCII 32);
</p>
</li>
<li>
<p>
ASCII decimal number that represents the number of subtrees this
    tree has;
</p>
</li>
<li>
<p>
A newline (ASCII 10); and
</p>
</li>
<li>
<p>
160-bit object name for the object that would result from writing
    this span of index as a tree.
</p>
<div class="literalblock">
<div class="content">
<pre><code>An entry can be in an invalidated state and is represented by having
a negative number in the entry_count field. In this case, there is no
object name and the next entry starts immediately after the newline.
When writing an invalid entry, -1 should always be used as entry_count.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The entries are written out in the top-down, depth-first order.  The
first entry represents the root level of the repository, followed by the
first subtree---let's call this A---of the root level (with its name
relative to the root level), followed by the first subtree of A (with
its name relative to A), ...</code></pre>
</div></div>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_resolve_undo">Resolve undo</h3>
<div class="literalblock">
<div class="content">
<pre><code>A conflict is represented in the index as a set of higher stage entries.
When a conflict is resolved (e.g. with "git add path"), these higher
stage entries will be removed and a stage-0 entry with proper resoluton
is added.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>When these higher stage entries are removed, they are saved in the
resolve undo extension, so that conflicts can be recreated (e.g. with
"git checkout -m"), in case users want to redo a conflict resolution
from scratch.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The signature for this extension is { 'R', 'E', 'U', 'C' }.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>A series of entries fill the entire extension; each of which
consists of:</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
NUL-terminated pathname the entry describes (relative to the root of
    the repository, i.e. full pathname);
</p>
</li>
<li>
<p>
Three NUL-terminated ASCII octal numbers, entry mode of entries in
    stage 1 to 3 (a missing stage is represented by "0" in this field);
    and
</p>
</li>
<li>
<p>
At most three 160-bit object names of the entry in stages from 1 to 3
    (nothing is written for a missing stage).
</p>
</li>
</ul></div>
</div>
</div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
Last updated 2013-06-10 20:01:55 UTC
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