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git-commit-vandalism/Documentation/git-cat-file.txt
Jeff King 97be04077f cat-file: only split on whitespace when %(rest) is used 
Commit c334b87b (cat-file: split --batch input lines on whitespace,
2013-07-11) taught `cat-file --batch-check` to split input lines on
the first whitespace, and stash everything after the first token
into the %(rest) output format element.  It claimed:

   Object names cannot contain spaces, so any input with
   spaces would have resulted in a "missing" line.

But that is not correct.  Refs, object sha1s, and various peeling
suffixes cannot contain spaces, but some object names can. In
particular:

  1. Tree paths like "[<tree>]:path with whitespace"

  2. Reflog specifications like "@{2 days ago}"

  3. Commit searches like "rev^{/grep me}" or ":/grep me"

To remain backwards compatible, we cannot split on whitespace by
default, hence we will ship 1.8.4 with the commit reverted.

Resurrect its attempt but in a weaker form; only do the splitting
when "%(rest)" is used in the output format. Since that element did
not exist at all before c334b87, old scripts cannot be affected.

The existence of object names with spaces does mean that you
cannot reliably do:

  echo ":path with space and other data" |
  git cat-file --batch-check="%(objectname) %(rest)"

as it would split the path and feed only ":path" to get_sha1. But
that command is nonsensical. If you wanted to see "and other data"
in "%(rest)", git cannot possibly know where the filename ends and
the "rest" begins.

It might be more robust to have something like "-z" to separate the
input elements. But this patch is still a reasonable step before
having that.  It makes the easy cases easy; people who do not care
about %(rest) do not have to consider it, and the %(rest) code
handles the spaces and newlines of "rev-list --objects" correctly.

Hard cases remain hard but possible (if you might get whitespace in
your input, you do not get to use %(rest) and must split and join
the output yourself using more flexible tools). And most
importantly, it does not preclude us from having different splitting
rules later if a "-z" (or similar) option is added.  So we can make
the hard cases easier later, if we choose to.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2013-08-05 09:30:48 -07:00

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git-cat-file(1)
===============
NAME
----
git-cat-file - Provide content or type and size information for repository objects
SYNOPSIS
--------
[verse]
'git cat-file' (-t | -s | -e | -p | <type> | --textconv ) <object>
'git cat-file' (--batch | --batch-check) < <list-of-objects>
DESCRIPTION
-----------
In its first form, the command provides the content or the type of an object in
the repository. The type is required unless '-t' or '-p' is used to find the
object type, or '-s' is used to find the object size, or '--textconv' is used
(which implies type "blob").
In the second form, a list of objects (separated by linefeeds) is provided on
stdin, and the SHA-1, type, and size of each object is printed on stdout.
OPTIONS
-------
<object>::
The name of the object to show.
For a more complete list of ways to spell object names, see
the "SPECIFYING REVISIONS" section in linkgit:gitrevisions[7].
-t::
Instead of the content, show the object type identified by
<object>.
-s::
Instead of the content, show the object size identified by
<object>.
-e::
Suppress all output; instead exit with zero status if <object>
exists and is a valid object.
-p::
Pretty-print the contents of <object> based on its type.
<type>::
Typically this matches the real type of <object> but asking
for a type that can trivially be dereferenced from the given
<object> is also permitted. An example is to ask for a
"tree" with <object> being a commit object that contains it,
or to ask for a "blob" with <object> being a tag object that
points at it.
--textconv::
Show the content as transformed by a textconv filter. In this case,
<object> has be of the form <treeish>:<path>, or :<path> in order
to apply the filter to the content recorded in the index at <path>.
--batch::
--batch=<format>::
Print object information and contents for each object provided
on stdin. May not be combined with any other options or arguments.
See the section `BATCH OUTPUT` below for details.
--batch-check::
--batch-check=<format>::
Print object information for each object provided on stdin. May
not be combined with any other options or arguments. See the
section `BATCH OUTPUT` below for details.
OUTPUT
------
If '-t' is specified, one of the <type>.
If '-s' is specified, the size of the <object> in bytes.
If '-e' is specified, no output.
If '-p' is specified, the contents of <object> are pretty-printed.
If <type> is specified, the raw (though uncompressed) contents of the <object>
will be returned.
BATCH OUTPUT
------------
If `--batch` or `--batch-check` is given, `cat-file` will read objects
from stdin, one per line, and print information about them. By default,
the whole line is considered as an object, as if it were fed to
linkgit:git-rev-parse[1].
You can specify the information shown for each object by using a custom
`<format>`. The `<format>` is copied literally to stdout for each
object, with placeholders of the form `%(atom)` expanded, followed by a
newline. The available atoms are:
`objectname`::
The 40-hex object name of the object.
`objecttype`::
The type of of the object (the same as `cat-file -t` reports).
`objectsize`::
The size, in bytes, of the object (the same as `cat-file -s`
reports).
`objectsize:disk`::
The size, in bytes, that the object takes up on disk. See the
note about on-disk sizes in the `CAVEATS` section below.
`rest`::
If this atom is used in the output string, input lines are split
at the first whitespace boundary. All characters before that
whitespace are considered to be the object name; characters
after that first run of whitespace (i.e., the "rest" of the
line) are output in place of the `%(rest)` atom.
If no format is specified, the default format is `%(objectname)
%(objecttype) %(objectsize)`.
If `--batch` is specified, the object information is followed by the
object contents (consisting of `%(objectsize)` bytes), followed by a
newline.
For example, `--batch` without a custom format would produce:
------------
<sha1> SP <type> SP <size> LF
<contents> LF
------------
Whereas `--batch-check='%(objectname) %(objecttype)'` would produce:
------------
<sha1> SP <type> LF
------------
If a name is specified on stdin that cannot be resolved to an object in
the repository, then `cat-file` will ignore any custom format and print:
------------
<object> SP missing LF
------------
CAVEATS
-------
Note that the sizes of objects on disk are reported accurately, but care
should be taken in drawing conclusions about which refs or objects are
responsible for disk usage. The size of a packed non-delta object may be
much larger than the size of objects which delta against it, but the
choice of which object is the base and which is the delta is arbitrary
and is subject to change during a repack. Note also that multiple copies
of an object may be present in the object database; in this case, it is
undefined which copy's size will be reported.
GIT
---
Part of the linkgit:git[1] suite
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