Merge "checkout ambiguous ref bugfix" into maint

[thirdparty/git.git] / Documentation / gitattributes.txt

gitattributes(5)
================

NAME
----
gitattributes - defining attributes per path

SYNOPSIS
--------
$GIT_DIR/info/attributes, .gitattributes


DESCRIPTION
-----------

A `gitattributes` file is a simple text file that gives
`attributes` to pathnames.

Each line in `gitattributes` file is of form:

	pattern	attr1 attr2 ...

That is, a pattern followed by an attributes list,
separated by whitespaces.  When the pattern matches the
path in question, the attributes listed on the line are given to
the path.

Each attribute can be in one of these states for a given path:

Set::

	The path has the attribute with special value "true";
	this is specified by listing only the name of the
	attribute in the attribute list.

Unset::

	The path has the attribute with special value "false";
	this is specified by listing the name of the attribute
	prefixed with a dash `-` in the attribute list.

Set to a value::

	The path has the attribute with specified string value;
	this is specified by listing the name of the attribute
	followed by an equal sign `=` and its value in the
	attribute list.

Unspecified::

	No pattern matches the path, and nothing says if
	the path has or does not have the attribute, the
	attribute for the path is said to be Unspecified.

When more than one pattern matches the path, a later line
overrides an earlier line.  This overriding is done per
attribute.  The rules how the pattern matches paths are the
same as in `.gitignore` files; see linkgit:gitignore[5].

When deciding what attributes are assigned to a path, git
consults `$GIT_DIR/info/attributes` file (which has the highest
precedence), `.gitattributes` file in the same directory as the
path in question, and its parent directories up to the toplevel of the
work tree (the further the directory that contains `.gitattributes`
is from the path in question, the lower its precedence). Finally
global and system-wide files are considered (they have the lowest
precedence).

If you wish to affect only a single repository (i.e., to assign
attributes to files that are particular to
one user's workflow for that repository), then
attributes should be placed in the `$GIT_DIR/info/attributes` file.
Attributes which should be version-controlled and distributed to other
repositories (i.e., attributes of interest to all users) should go into
`.gitattributes` files. Attributes that should affect all repositories
for a single user should be placed in a file specified by the
`core.attributesfile` configuration option (see linkgit:git-config[1]).
Attributes for all users on a system should be placed in the
`$(prefix)/etc/gitattributes` file.

Sometimes you would need to override an setting of an attribute
for a path to `unspecified` state.  This can be done by listing
the name of the attribute prefixed with an exclamation point `!`.


EFFECTS
-------

Certain operations by git can be influenced by assigning
particular attributes to a path.  Currently, the following
operations are attributes-aware.

Checking-out and checking-in
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

These attributes affect how the contents stored in the
repository are copied to the working tree files when commands
such as 'git checkout' and 'git merge' run.  They also affect how
git stores the contents you prepare in the working tree in the
repository upon 'git add' and 'git commit'.

`text`
^^^^^^

This attribute enables and controls end-of-line normalization.  When a
text file is normalized, its line endings are converted to LF in the
repository.  To control what line ending style is used in the working
directory, use the `eol` attribute for a single file and the
`core.eol` configuration variable for all text files.

Set::

	Setting the `text` attribute on a path enables end-of-line
	normalization and marks the path as a text file.  End-of-line
	conversion takes place without guessing the content type.

Unset::

	Unsetting the `text` attribute on a path tells git not to
	attempt any end-of-line conversion upon checkin or checkout.

Set to string value "auto"::

	When `text` is set to "auto", the path is marked for automatic
	end-of-line normalization.  If git decides that the content is
	text, its line endings are normalized to LF on checkin.

Unspecified::

	If the `text` attribute is unspecified, git uses the
	`core.autocrlf` configuration variable to determine if the
	file should be converted.

Any other value causes git to act as if `text` has been left
unspecified.

`eol`
^^^^^

This attribute sets a specific line-ending style to be used in the
working directory.  It enables end-of-line normalization without any
content checks, effectively setting the `text` attribute.

Set to string value "crlf"::

	This setting forces git to normalize line endings for this
	file on checkin and convert them to CRLF when the file is
	checked out.

Set to string value "lf"::

	This setting forces git to normalize line endings to LF on
	checkin and prevents conversion to CRLF when the file is
	checked out.

Backwards compatibility with `crlf` attribute
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For backwards compatibility, the `crlf` attribute is interpreted as
follows:

------------------------
crlf		text
-crlf		-text
crlf=input	eol=lf
------------------------

End-of-line conversion
^^^^^^^^^^^^^^^^^^^^^^

While git normally leaves file contents alone, it can be configured to
normalize line endings to LF in the repository and, optionally, to
convert them to CRLF when files are checked out.

Here is an example that will make git normalize .txt, .vcproj and .sh
files, ensure that .vcproj files have CRLF and .sh files have LF in
the working directory, and prevent .jpg files from being normalized
regardless of their content.

------------------------
*.txt		text
*.vcproj	eol=crlf
*.sh		eol=lf
*.jpg		-text
------------------------

Other source code management systems normalize all text files in their
repositories, and there are two ways to enable similar automatic
normalization in git.

If you simply want to have CRLF line endings in your working directory
regardless of the repository you are working with, you can set the
config variable "core.autocrlf" without changing any attributes.

------------------------
[core]
	autocrlf = true
------------------------

This does not force normalization of all text files, but does ensure
that text files that you introduce to the repository have their line
endings normalized to LF when they are added, and that files that are
already normalized in the repository stay normalized.

If you want to interoperate with a source code management system that
enforces end-of-line normalization, or you simply want all text files
in your repository to be normalized, you should instead set the `text`
attribute to "auto" for _all_ files.

------------------------
*	text=auto
------------------------

This ensures that all files that git considers to be text will have
normalized (LF) line endings in the repository.  The `core.eol`
configuration variable controls which line endings git will use for
normalized files in your working directory; the default is to use the
native line ending for your platform, or CRLF if `core.autocrlf` is
set.

NOTE: When `text=auto` normalization is enabled in an existing
repository, any text files containing CRLFs should be normalized.  If
they are not they will be normalized the next time someone tries to
change them, causing unfortunate misattribution.  From a clean working
directory:

-------------------------------------------------
$ echo "* text=auto" >>.gitattributes
$ rm .git/index     # Remove the index to force git to
$ git reset         # re-scan the working directory
$ git status        # Show files that will be normalized
$ git add -u
$ git add .gitattributes
$ git commit -m "Introduce end-of-line normalization"
-------------------------------------------------

If any files that should not be normalized show up in 'git status',
unset their `text` attribute before running 'git add -u'.

------------------------
manual.pdf	-text
------------------------

Conversely, text files that git does not detect can have normalization
enabled manually.

------------------------
weirdchars.txt	text
------------------------

If `core.safecrlf` is set to "true" or "warn", git verifies if
the conversion is reversible for the current setting of
`core.autocrlf`.  For "true", git rejects irreversible
conversions; for "warn", git only prints a warning but accepts
an irreversible conversion.  The safety triggers to prevent such
a conversion done to the files in the work tree, but there are a
few exceptions.  Even though...

- 'git add' itself does not touch the files in the work tree, the
  next checkout would, so the safety triggers;

- 'git apply' to update a text file with a patch does touch the files
  in the work tree, but the operation is about text files and CRLF
  conversion is about fixing the line ending inconsistencies, so the
  safety does not trigger;

- 'git diff' itself does not touch the files in the work tree, it is
  often run to inspect the changes you intend to next 'git add'.  To
  catch potential problems early, safety triggers.


`ident`
^^^^^^^

When the attribute `ident` is set for a path, git replaces
`$Id$` in the blob object with `$Id:`, followed by the
40-character hexadecimal blob object name, followed by a dollar
sign `$` upon checkout.  Any byte sequence that begins with
`$Id:` and ends with `$` in the worktree file is replaced
with `$Id$` upon check-in.


`filter`
^^^^^^^^

A `filter` attribute can be set to a string value that names a
filter driver specified in the configuration.

A filter driver consists of a `clean` command and a `smudge`
command, either of which can be left unspecified.  Upon
checkout, when the `smudge` command is specified, the command is
fed the blob object from its standard input, and its standard
output is used to update the worktree file.  Similarly, the
`clean` command is used to convert the contents of worktree file
upon checkin.

A missing filter driver definition in the config is not an error
but makes the filter a no-op passthru.

The content filtering is done to massage the content into a
shape that is more convenient for the platform, filesystem, and
the user to use.  The key phrase here is "more convenient" and not
"turning something unusable into usable".  In other words, the
intent is that if someone unsets the filter driver definition,
or does not have the appropriate filter program, the project
should still be usable.

For example, in .gitattributes, you would assign the `filter`
attribute for paths.

------------------------
*.c	filter=indent
------------------------

Then you would define a "filter.indent.clean" and "filter.indent.smudge"
configuration in your .git/config to specify a pair of commands to
modify the contents of C programs when the source files are checked
in ("clean" is run) and checked out (no change is made because the
command is "cat").

------------------------
[filter "indent"]
	clean = indent
	smudge = cat
------------------------

For best results, `clean` should not alter its output further if it is
run twice ("clean->clean" should be equivalent to "clean"), and
multiple `smudge` commands should not alter `clean`'s output
("smudge->smudge->clean" should be equivalent to "clean").  See the
section on merging below.

The "indent" filter is well-behaved in this regard: it will not modify
input that is already correctly indented.  In this case, the lack of a
smudge filter means that the clean filter _must_ accept its own output
without modifying it.

Sequence "%f" on the filter command line is replaced with the name of
the file the filter is working on.  A filter might use this in keyword
substitution.  For example:

------------------------
[filter "p4"]
	clean = git-p4-filter --clean %f
	smudge = git-p4-filter --smudge %f
------------------------


Interaction between checkin/checkout attributes
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In the check-in codepath, the worktree file is first converted
with `filter` driver (if specified and corresponding driver
defined), then the result is processed with `ident` (if
specified), and then finally with `text` (again, if specified
and applicable).

In the check-out codepath, the blob content is first converted
with `text`, and then `ident` and fed to `filter`.


Merging branches with differing checkin/checkout attributes
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you have added attributes to a file that cause the canonical
repository format for that file to change, such as adding a
clean/smudge filter or text/eol/ident attributes, merging anything
where the attribute is not in place would normally cause merge
conflicts.

To prevent these unnecessary merge conflicts, git can be told to run a
virtual check-out and check-in of all three stages of a file when
resolving a three-way merge by setting the `merge.renormalize`
configuration variable.  This prevents changes caused by check-in
conversion from causing spurious merge conflicts when a converted file
is merged with an unconverted file.

As long as a "smudge->clean" results in the same output as a "clean"
even on files that are already smudged, this strategy will
automatically resolve all filter-related conflicts.  Filters that do
not act in this way may cause additional merge conflicts that must be
resolved manually.


Generating diff text
~~~~~~~~~~~~~~~~~~~~

`diff`
^^^^^^

The attribute `diff` affects how 'git' generates diffs for particular
files. It can tell git whether to generate a textual patch for the path
or to treat the path as a binary file.  It can also affect what line is
shown on the hunk header `@@ -k,l +n,m @@` line, tell git to use an
external command to generate the diff, or ask git to convert binary
files to a text format before generating the diff.

Set::

	A path to which the `diff` attribute is set is treated
	as text, even when they contain byte values that
	normally never appear in text files, such as NUL.

Unset::

	A path to which the `diff` attribute is unset will
	generate `Binary files differ` (or a binary patch, if
	binary patches are enabled).

Unspecified::

	A path to which the `diff` attribute is unspecified
	first gets its contents inspected, and if it looks like
	text, it is treated as text.  Otherwise it would
	generate `Binary files differ`.

String::

	Diff is shown using the specified diff driver.  Each driver may
	specify one or more options, as described in the following
	section. The options for the diff driver "foo" are defined
	by the configuration variables in the "diff.foo" section of the
	git config file.


Defining an external diff driver
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The definition of a diff driver is done in `gitconfig`, not
`gitattributes` file, so strictly speaking this manual page is a
wrong place to talk about it.  However...

To define an external diff driver `jcdiff`, add a section to your
`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:

----------------------------------------------------------------
[diff "jcdiff"]
	command = j-c-diff
----------------------------------------------------------------

When git needs to show you a diff for the path with `diff`
attribute set to `jcdiff`, it calls the command you specified
with the above configuration, i.e. `j-c-diff`, with 7
parameters, just like `GIT_EXTERNAL_DIFF` program is called.
See linkgit:git[1] for details.


Defining a custom hunk-header
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Each group of changes (called a "hunk") in the textual diff output
is prefixed with a line of the form:

	@@ -k,l +n,m @@ TEXT

This is called a 'hunk header'.  The "TEXT" portion is by default a line
that begins with an alphabet, an underscore or a dollar sign; this
matches what GNU 'diff -p' output uses.  This default selection however
is not suited for some contents, and you can use a customized pattern
to make a selection.

First, in .gitattributes, you would assign the `diff` attribute
for paths.

------------------------
*.tex	diff=tex
------------------------

Then, you would define a "diff.tex.xfuncname" configuration to
specify a regular expression that matches a line that you would
want to appear as the hunk header "TEXT". Add a section to your
`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:

------------------------
[diff "tex"]
	xfuncname = "^(\\\\(sub)*section\\{.*)$"
------------------------

Note.  A single level of backslashes are eaten by the
configuration file parser, so you would need to double the
backslashes; the pattern above picks a line that begins with a
backslash, and zero or more occurrences of `sub` followed by
`section` followed by open brace, to the end of line.

There are a few built-in patterns to make this easier, and `tex`
is one of them, so you do not have to write the above in your
configuration file (you still need to enable this with the
attribute mechanism, via `.gitattributes`).  The following built in
patterns are available:

- `bibtex` suitable for files with BibTeX coded references.

- `cpp` suitable for source code in the C and C++ languages.

- `csharp` suitable for source code in the C# language.

- `fortran` suitable for source code in the Fortran language.

- `html` suitable for HTML/XHTML documents.

- `java` suitable for source code in the Java language.

- `objc` suitable for source code in the Objective-C language.

- `pascal` suitable for source code in the Pascal/Delphi language.

- `perl` suitable for source code in the Perl language.

- `php` suitable for source code in the PHP language.

- `python` suitable for source code in the Python language.

- `ruby` suitable for source code in the Ruby language.

- `tex` suitable for source code for LaTeX documents.


Customizing word diff
^^^^^^^^^^^^^^^^^^^^^

You can customize the rules that `git diff --word-diff` uses to
split words in a line, by specifying an appropriate regular expression
in the "diff.*.wordRegex" configuration variable.  For example, in TeX
a backslash followed by a sequence of letters forms a command, but
several such commands can be run together without intervening
whitespace.  To separate them, use a regular expression in your
`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:

------------------------
[diff "tex"]
	wordRegex = "\\\\[a-zA-Z]+|[{}]|\\\\.|[^\\{}[:space:]]+"
------------------------

A built-in pattern is provided for all languages listed in the
previous section.


Performing text diffs of binary files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Sometimes it is desirable to see the diff of a text-converted
version of some binary files. For example, a word processor
document can be converted to an ASCII text representation, and
the diff of the text shown. Even though this conversion loses
some information, the resulting diff is useful for human
viewing (but cannot be applied directly).

The `textconv` config option is used to define a program for
performing such a conversion. The program should take a single
argument, the name of a file to convert, and produce the
resulting text on stdout.

For example, to show the diff of the exif information of a
file instead of the binary information (assuming you have the
exif tool installed), add the following section to your
`$GIT_DIR/config` file (or `$HOME/.gitconfig` file):

------------------------
[diff "jpg"]
	textconv = exif
------------------------

NOTE: The text conversion is generally a one-way conversion;
in this example, we lose the actual image contents and focus
just on the text data. This means that diffs generated by
textconv are _not_ suitable for applying. For this reason,
only `git diff` and the `git log` family of commands (i.e.,
log, whatchanged, show) will perform text conversion. `git
format-patch` will never generate this output. If you want to
send somebody a text-converted diff of a binary file (e.g.,
because it quickly conveys the changes you have made), you
should generate it separately and send it as a comment _in
addition to_ the usual binary diff that you might send.

Because text conversion can be slow, especially when doing a
large number of them with `git log -p`, git provides a mechanism
to cache the output and use it in future diffs.  To enable
caching, set the "cachetextconv" variable in your diff driver's
config. For example:

------------------------
[diff "jpg"]
	textconv = exif
	cachetextconv = true
------------------------

This will cache the result of running "exif" on each blob
indefinitely. If you change the textconv config variable for a
diff driver, git will automatically invalidate the cache entries
and re-run the textconv filter. If you want to invalidate the
cache manually (e.g., because your version of "exif" was updated
and now produces better output), you can remove the cache
manually with `git update-ref -d refs/notes/textconv/jpg` (where
"jpg" is the name of the diff driver, as in the example above).

Marking files as binary
^^^^^^^^^^^^^^^^^^^^^^^

Git usually guesses correctly whether a blob contains text or binary
data by examining the beginning of the contents. However, sometimes you
may want to override its decision, either because a blob contains binary
data later in the file, or because the content, while technically
composed of text characters, is opaque to a human reader. For example,
many postscript files contain only ascii characters, but produce noisy
and meaningless diffs.

The simplest way to mark a file as binary is to unset the diff
attribute in the `.gitattributes` file:

------------------------
*.ps -diff
------------------------

This will cause git to generate `Binary files differ` (or a binary
patch, if binary patches are enabled) instead of a regular diff.

However, one may also want to specify other diff driver attributes. For
example, you might want to use `textconv` to convert postscript files to
an ascii representation for human viewing, but otherwise treat them as
binary files. You cannot specify both `-diff` and `diff=ps` attributes.
The solution is to use the `diff.*.binary` config option:

------------------------
[diff "ps"]
  textconv = ps2ascii
  binary = true
------------------------

Performing a three-way merge
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`merge`
^^^^^^^

The attribute `merge` affects how three versions of a file are
merged when a file-level merge is necessary during `git merge`,
and other commands such as `git revert` and `git cherry-pick`.

Set::

	Built-in 3-way merge driver is used to merge the
	contents in a way similar to 'merge' command of `RCS`
	suite.  This is suitable for ordinary text files.

Unset::

	Take the version from the current branch as the
	tentative merge result, and declare that the merge has
	conflicts.  This is suitable for binary files that do
	not have a well-defined merge semantics.

Unspecified::

	By default, this uses the same built-in 3-way merge
	driver as is the case when the `merge` attribute is set.
	However, the `merge.default` configuration variable can name
	different merge driver to be used with paths for which the
	`merge` attribute is unspecified.

String::

	3-way merge is performed using the specified custom
	merge driver.  The built-in 3-way merge driver can be
	explicitly specified by asking for "text" driver; the
	built-in "take the current branch" driver can be
	requested with "binary".


Built-in merge drivers
^^^^^^^^^^^^^^^^^^^^^^

There are a few built-in low-level merge drivers defined that
can be asked for via the `merge` attribute.

text::

	Usual 3-way file level merge for text files.  Conflicted
	regions are marked with conflict markers `<<<<<<<`,
	`=======` and `>>>>>>>`.  The version from your branch
	appears before the `=======` marker, and the version
	from the merged branch appears after the `=======`
	marker.

binary::

	Keep the version from your branch in the work tree, but
	leave the path in the conflicted state for the user to
	sort out.

union::

	Run 3-way file level merge for text files, but take
	lines from both versions, instead of leaving conflict
	markers.  This tends to leave the added lines in the
	resulting file in random order and the user should
	verify the result. Do not use this if you do not
	understand the implications.


Defining a custom merge driver
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The definition of a merge driver is done in the `.git/config`
file, not in the `gitattributes` file, so strictly speaking this
manual page is a wrong place to talk about it.  However...

To define a custom merge driver `filfre`, add a section to your
`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:

----------------------------------------------------------------
[merge "filfre"]
	name = feel-free merge driver
	driver = filfre %O %A %B
	recursive = binary
----------------------------------------------------------------

The `merge.*.name` variable gives the driver a human-readable
name.

The `merge.*.driver` variable's value is used to construct a
command to run to merge ancestor's version (`%O`), current
version (`%A`) and the other branches' version (`%B`).  These
three tokens are replaced with the names of temporary files that
hold the contents of these versions when the command line is
built. Additionally, %L will be replaced with the conflict marker
size (see below).

The merge driver is expected to leave the result of the merge in
the file named with `%A` by overwriting it, and exit with zero
status if it managed to merge them cleanly, or non-zero if there
were conflicts.

The `merge.*.recursive` variable specifies what other merge
driver to use when the merge driver is called for an internal
merge between common ancestors, when there are more than one.
When left unspecified, the driver itself is used for both
internal merge and the final merge.


`conflict-marker-size`
^^^^^^^^^^^^^^^^^^^^^^

This attribute controls the length of conflict markers left in
the work tree file during a conflicted merge.  Only setting to
the value to a positive integer has any meaningful effect.

For example, this line in `.gitattributes` can be used to tell the merge
machinery to leave much longer (instead of the usual 7-character-long)
conflict markers when merging the file `Documentation/git-merge.txt`
results in a conflict.

------------------------
Documentation/git-merge.txt	conflict-marker-size=32
------------------------


Checking whitespace errors
~~~~~~~~~~~~~~~~~~~~~~~~~~

`whitespace`
^^^^^^^^^^^^

The `core.whitespace` configuration variable allows you to define what
'diff' and 'apply' should consider whitespace errors for all paths in
the project (See linkgit:git-config[1]).  This attribute gives you finer
control per path.

Set::

	Notice all types of potential whitespace errors known to git.
	The tab width is taken from the value of the `core.whitespace`
	configuration variable.

Unset::

	Do not notice anything as error.

Unspecified::

	Use the value of the `core.whitespace` configuration variable to
	decide what to notice as error.

String::

	Specify a comma separate list of common whitespace problems to
	notice in the same format as the `core.whitespace` configuration
	variable.


Creating an archive
~~~~~~~~~~~~~~~~~~~

`export-ignore`
^^^^^^^^^^^^^^^

Files and directories with the attribute `export-ignore` won't be added to
archive files.

`export-subst`
^^^^^^^^^^^^^^

If the attribute `export-subst` is set for a file then git will expand
several placeholders when adding this file to an archive.  The
expansion depends on the availability of a commit ID, i.e., if
linkgit:git-archive[1] has been given a tree instead of a commit or a
tag then no replacement will be done.  The placeholders are the same
as those for the option `--pretty=format:` of linkgit:git-log[1],
except that they need to be wrapped like this: `$Format:PLACEHOLDERS$`
in the file.  E.g. the string `$Format:%H$` will be replaced by the
commit hash.


Packing objects
~~~~~~~~~~~~~~~

`delta`
^^^^^^^

Delta compression will not be attempted for blobs for paths with the
attribute `delta` set to false.


Viewing files in GUI tools
~~~~~~~~~~~~~~~~~~~~~~~~~~

`encoding`
^^^^^^^^^^

The value of this attribute specifies the character encoding that should
be used by GUI tools (e.g. linkgit:gitk[1] and linkgit:git-gui[1]) to
display the contents of the relevant file. Note that due to performance
considerations linkgit:gitk[1] does not use this attribute unless you
manually enable per-file encodings in its options.

If this attribute is not set or has an invalid value, the value of the
`gui.encoding` configuration variable is used instead
(See linkgit:git-config[1]).


USING ATTRIBUTE MACROS
----------------------

You do not want any end-of-line conversions applied to, nor textual diffs
produced for, any binary file you track.  You would need to specify e.g.

------------
*.jpg -text -diff
------------

but that may become cumbersome, when you have many attributes.  Using
attribute macros, you can specify groups of attributes set or unset at
the same time.  The system knows a built-in attribute macro, `binary`:

------------
*.jpg binary
------------

which is equivalent to the above.  Note that the attribute macros can only
be "Set" (see the above example that sets "binary" macro as if it were an
ordinary attribute --- setting it in turn unsets "text" and "diff").


DEFINING ATTRIBUTE MACROS
-------------------------

Custom attribute macros can be defined only in the `.gitattributes` file
at the toplevel (i.e. not in any subdirectory).  The built-in attribute
macro "binary" is equivalent to:

------------
[attr]binary -diff -text
------------


EXAMPLE
-------

If you have these three `gitattributes` file:

----------------------------------------------------------------
(in $GIT_DIR/info/attributes)

a*	foo !bar -baz

(in .gitattributes)
abc	foo bar baz

(in t/.gitattributes)
ab*	merge=filfre
abc	-foo -bar
*.c	frotz
----------------------------------------------------------------

the attributes given to path `t/abc` are computed as follows:

1. By examining `t/.gitattributes` (which is in the same
   directory as the path in question), git finds that the first
   line matches.  `merge` attribute is set.  It also finds that
   the second line matches, and attributes `foo` and `bar`
   are unset.

2. Then it examines `.gitattributes` (which is in the parent
   directory), and finds that the first line matches, but
   `t/.gitattributes` file already decided how `merge`, `foo`
   and `bar` attributes should be given to this path, so it
   leaves `foo` and `bar` unset.  Attribute `baz` is set.

3. Finally it examines `$GIT_DIR/info/attributes`.  This file
   is used to override the in-tree settings.  The first line is
   a match, and `foo` is set, `bar` is reverted to unspecified
   state, and `baz` is unset.

As the result, the attributes assignment to `t/abc` becomes:

----------------------------------------------------------------
foo	set to true
bar	unspecified
baz	set to false
merge	set to string value "filfre"
frotz	unspecified
----------------------------------------------------------------



GIT
---
Part of the linkgit:git[1] suite