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git/Documentation/git-cat-file.adoc
Pablo Sabater 5b591f977f cat-file: validate remote atoms with allow_list 
strstr() is not enough to validate the format placeholders in
remote-object-info causing two errors:

- Atoms recognized by expand_atom() but the remote doesn't returns 1, but
  data->type contains garbage causing segfault.
- expand_atom() returns 0 for unknown atoms, calling
  strbuf_expand_bad_format() which ends in die() blocking local queries
  if the same format is shared.

Add an allow_list with the supported atoms at the top of expand_atom().
In remote mode, unsupported atoms return 1 leaving the sb empty,
honoring how for-each-ref handles known but inapplicable atoms.

As extra safety, initialize data->type to OBJ_BAD and add a NULL check
for type_name() so uninitialized data doesn't cause segfault.

Update tests that expect previous die() behaviour to expect an empty
string and add an explicit test for empty string return on unknown
placeholder.

Update caveat behaviour documentation.

Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Mentored-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Pablo Sabater <pabloosabaterr@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2026-06-08 23:30:15 +09:00

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git-cat-file(1)
===============
NAME
----
git-cat-file - Provide contents or details of repository objects
SYNOPSIS
--------
[verse]
'git cat-file' <type> <object>
'git cat-file' (-e | -p | -t | -s) <object>
'git cat-file' (--textconv | --filters)
[<rev>:<path|tree-ish> | --path=<path|tree-ish> <rev>]
'git cat-file' (--batch | --batch-check | --batch-command) [--batch-all-objects]
[--buffer] [--follow-symlinks] [--unordered]
[--textconv | --filters] [-Z]
DESCRIPTION
-----------
Output the contents or other properties such as size, type or delta
information of one or more objects.
This command can operate in two modes, depending on whether an option
from the `--batch` family is specified.
In non-batch mode, the command provides information on an object
named on the command line.
In batch mode, arguments are read from standard input.
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>`. If used with `--use-mailmap` option, will show
the size of updated object after replacing idents using the
mailmap mechanism.
-e::
Exit with zero status if `<object>` exists and is a valid
object. If `<object>` is of an invalid format, exit with non-zero
status and emit an error on stderr.
-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.
--mailmap::
--no-mailmap::
--use-mailmap::
--no-use-mailmap::
Use mailmap file to map author, committer and tagger names
and email addresses to canonical real names and email addresses.
See linkgit:git-shortlog[1].
--textconv::
Show the content as transformed by a textconv filter. In this case,
`<object>` has to be of the form `<tree-ish>:<path>`, or `:<path>` in
order to apply the filter to the content recorded in the index at
`<path>`.
--filters::
Show the content as converted by the filters configured in
the current working tree for the given `<path>` (i.e. smudge filters,
end-of-line conversion, etc). In this case, `<object>` has to be of
the form `<tree-ish>:<path>`, or `:<path>`.
--filter=<filter-spec>::
--no-filter::
Omit objects from the list of printed objects. This can only be used in
combination with one of the batched modes. Excluded objects that have
been explicitly requested via any of the batch modes that read objects
via standard input (`--batch`, `--batch-check`) will be reported as
"filtered". Excluded objects in `--batch-all-objects` mode will not be
printed at all. The '<filter-spec>' may be one of the following:
+
The form '--filter=blob:none' omits all blobs.
+
The form '--filter=blob:limit=<n>[kmg]' omits blobs of size at least n
bytes or units. n may be zero. The suffixes k, m, and g can be used to name
units in KiB, MiB, or GiB. For example, 'blob:limit=1k' is the same as
'blob:limit=1024'.
+
The form '--filter=object:type=(tag|commit|tree|blob)' omits all objects which
are not of the requested type.
--path=<path>::
For use with `--textconv` or `--filters`, to allow specifying an object
name and a path separately, e.g. when it is difficult to figure out
the revision from which the blob came.
--batch::
--batch=<format>::
Print object information and contents for each object provided
on stdin. May not be combined with any other options or arguments
except `--textconv`, `--filters`, or `--use-mailmap`.
+
--
* When used with `--textconv` or `--filters`, the input lines
must specify the path, separated by whitespace. See the section
`BATCH OUTPUT` below for details.
* When used with `--use-mailmap`, for commit and tag objects, the
contents part of the output shows the identities replaced using the
mailmap mechanism, while the information part of the output shows
the size of the object as if it actually recorded the replacement
identities.
--
--batch-check::
--batch-check=<format>::
Print object information for each object provided on stdin. May not be
combined with any other options or arguments except `--textconv`, `--filters`
or `--use-mailmap`.
+
--
* When used with `--textconv` or `--filters`, the input lines must
specify the path, separated by whitespace. See the section
`BATCH OUTPUT` below for details.
* When used with `--use-mailmap`, for commit and tag objects, the
printed object information shows the size of the object as if the
identities recorded in it were replaced by the mailmap mechanism.
--
--batch-command::
--batch-command=<format>::
Enter a command mode that reads commands and arguments from stdin. May
only be combined with `--buffer`, `--textconv`, `--use-mailmap` or
`--filters`.
+
--
* When used with `--textconv` or `--filters`, the input lines must
specify the path, separated by whitespace. See the section
`BATCH OUTPUT` below for details.
* When used with `--use-mailmap`, for commit and tag objects, the
`contents` command shows the identities replaced using the
mailmap mechanism, while the `info` command shows the size
of the object as if it actually recorded the replacement
identities.
--
+
`--batch-command` recognizes the following commands:
+
--
contents <object>::
Print object contents for object reference `<object>`. This corresponds to
the output of `--batch`.
info <object>::
Print object info for object reference `<object>`. This corresponds to the
output of `--batch-check`.
remote-object-info <remote> <object>...::
Print object info for object references `<object>` at specified
`<remote>` without downloading objects from the remote.
Raise an error when the `object-info` capability is not supported by the remote.
Raise an error when no object references are provided.
This command may be combined with `--buffer`.
flush::
Used with `--buffer` to execute all preceding commands that were issued
since the beginning or since the last flush was issued. When `--buffer`
is used, no output will come until a `flush` is issued. When `--buffer`
is not used, commands are flushed each time without issuing `flush`.
`mailmap (<bool>)`::
Enable or disable mailmap for subsequent commands. The `<bool>`
argument accepts the same boolean values as linkgit:git-config[1].
The mailmap data is read upon the first use and only once.
--
+
--batch-all-objects::
Instead of reading a list of objects on stdin, perform the
requested batch operation on all objects in the repository and
any alternate object stores (not just reachable objects).
Requires `--batch` or `--batch-check` be specified. By default,
the objects are visited in order sorted by their hashes; see
also `--unordered` below. Objects are presented as-is, without
respecting the "replace" mechanism of linkgit:git-replace[1].
--buffer::
Normally batch output is flushed after each object is output, so
that a process can interactively read and write from
`cat-file`. With this option, the output uses normal stdio
buffering; this is much more efficient when invoking
`--batch-check` or `--batch-command` on a large number of objects.
--unordered::
When `--batch-all-objects` is in use, visit objects in an
order which may be more efficient for accessing the object
contents than hash order. The exact details of the order are
unspecified, but if you do not require a specific order, this
should generally result in faster output, especially with
`--batch`. Note that `cat-file` will still show each object
only once, even if it is stored multiple times in the
repository.
--follow-symlinks::
With `--batch` or `--batch-check`, follow symlinks inside the
repository when requesting objects with extended SHA-1
expressions of the form tree-ish:path-in-tree. Instead of
providing output about the link itself, provide output about
the linked-to object. If a symlink points outside the
tree-ish (e.g. a link to `/foo` or a root-level link to `../foo`),
the portion of the link which is outside the tree will be
printed.
+
This option does not (currently) work correctly when an object in the
index is specified (e.g. `:link` instead of `HEAD:link`) rather than
one in the tree.
+
This option cannot (currently) be used unless `--batch` or
`--batch-check` is used.
+
For example, consider a git repository containing:
+
--
f: a file containing "hello\n"
link: a symlink to f
dir/link: a symlink to ../f
plink: a symlink to ../f
alink: a symlink to /etc/passwd
--
+
For a regular file `f`, `echo HEAD:f | git cat-file --batch` would print
+
--
ce013625030ba8dba906f756967f9e9ca394464a blob 6
--
+
And `echo HEAD:link | git cat-file --batch --follow-symlinks` would
print the same thing, as would `HEAD:dir/link`, as they both point at
`HEAD:f`.
+
Without `--follow-symlinks`, these would print data about the symlink
itself. In the case of `HEAD:link`, you would see
+
--
4d1ae35ba2c8ec712fa2a379db44ad639ca277bd blob 1
--
+
Both `plink` and `alink` point outside the tree, so they would
respectively print:
+
--
symlink 4
../f
symlink 11
/etc/passwd
--
-Z::
Only meaningful with `--batch`, `--batch-check`, or
`--batch-command`; input and output is NUL-delimited instead of
newline-delimited.
-z::
Only meaningful with `--batch`, `--batch-check`, or
`--batch-command`; input is NUL-delimited instead of
newline-delimited. This option is deprecated in favor of
`-Z` as the output can otherwise be ambiguous.
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, unless the `<object>` is malformed.
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 in the same
order as they have been read. By default, the whole line is
considered as an object, as if it were fed to linkgit:git-rev-parse[1].
When `--batch-command` is given, `cat-file` will read commands from stdin,
one per line, and print information based on the command given. With
`--batch-command`, the `info` command followed by an object will print
information about the object the same way `--batch-check` would, and the
`contents` command followed by an object prints contents in the same way
`--batch` would.
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 full hex representation of the object name.
`objecttype`::
The type of the object (the same as `cat-file -t` reports). See
`CAVEATS` below. Not supported by `remote-object-info`.
`objectmode`::
If the specified object has mode information (such as a tree or
index entry), the mode expressed as an octal integer. Otherwise,
empty string.
`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. Not
supported by `remote-object-info`.
`deltabase`::
If the object is stored as a delta on-disk, this expands to the
full hex representation of the delta base object name.
Otherwise, expands to the null OID (all zeroes). See `CAVEATS`
below. Not supported by `remote-object-info`.
`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)`, except for `remote-object-info` commands which use
`%(objectname) %(objectsize)` for now because "%(objecttype)" is not supported yet.
WARNING: When "%(objecttype)" is supported, the default format WILL be unified, so
DO NOT RELY on the current default format to stay the same!!!
If `--batch` is specified, or if `--batch-command` is used with the `contents`
command, 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:
-----------
<oid> SP <type> SP <size> LF
<contents> LF
-----------
Whereas `--batch-check='%(objectname) %(objecttype)'` would produce:
------------
<oid> 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
------------
If a name is specified on stdin that is filtered out via `--filter=`,
then `cat-file` will ignore any custom format and print:
------------
<object> SP excluded LF
------------
If a name is specified that might refer to more than one object (an ambiguous short sha), then `cat-file` will ignore any custom format and print:
------------
<object> SP ambiguous LF
------------
If a name is specified that refers to a submodule entry in a tree and the
target object does not exist in the repository, then `cat-file` will ignore
any custom format and print (with the object ID of the submodule):
------------
<oid> SP submodule LF
------------
If `--follow-symlinks` is used, and a symlink in the repository points
outside the repository, then `cat-file` will ignore any custom format
and print:
------------
symlink SP <size> LF
<symlink> LF
------------
The symlink will either be absolute (beginning with a `/`), or relative
to the tree root. For instance, if dir/link points to `../../foo`, then
`<symlink>` will be `../foo`. `<size>` is the size of the symlink in bytes.
If `--follow-symlinks` is used, the following error messages will be
displayed:
------------
<object> SP missing LF
------------
is printed when the initial symlink requested does not exist.
------------
dangling SP <size> LF
<object> LF
------------
is printed when the initial symlink exists, but something that
it (transitive-of) points to does not.
------------
loop SP <size> LF
<object> LF
------------
is printed for symlink loops (or any symlinks that
require more than 40 link resolutions to resolve).
------------
notdir SP <size> LF
<object> LF
------------
is printed when, during symlink resolution, a file is used as a
directory name.
Alternatively, when `-Z` is passed, the line feeds in any of the above examples
are replaced with NUL terminators. This ensures that output will be parsable if
the output itself would contain a linefeed and is thus recommended for
scripting purposes.
CAVEATS
-------
Note that since %(objecttype), %(objectsize:disk) and %(deltabase) are
currently not supported by the `remote-object-info` command, they will
return an empty string for remote queries, matching how `for-each-ref`
behaves for known but inapplicable placeholders.
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 or delta base
will be reported.
GIT
---
Part of the linkgit:git[1] suite
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