Document --unified/-U option

[git/mjg.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:

        glob    attr1 attr2 ...

That is, a glob pattern followed by an attributes list,
separated by whitespaces.  When the glob 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 glob 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 glob pattern matches the path, a later line
overrides an earlier line.  This overriding is done per
attribute.

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 (the further the
directory that contains `.gitattributes` is from the path in
question, the lower its precedence).

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`.

`crlf`
^^^^^^

This attribute controls the line-ending convention.

Set::

        Setting the `crlf` attribute on a path is meant to mark
        the path as a "text" file.  'core.autocrlf' conversion
        takes place without guessing the content type by
        inspection.

Unset::

        Unsetting the `crlf` attribute on a path is meant to
        mark the path as a "binary" file.  The path never goes
        through line endings conversion upon checkin/checkout.

Unspecified::

        Unspecified `crlf` attribute tells git to apply the
        `core.autocrlf` conversion when the file content looks
        like text.

Set to string value "input"::

        This is similar to setting the attribute to `true`, but
        also forces git to act as if `core.autocrlf` is set to
        `input` for the path.

Any other value set to `crlf` attribute is ignored and git acts
as if the attribute is left unspecified.


The `core.autocrlf` conversion
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If the configuration variable `core.autocrlf` is false, no
conversion is done.

When `core.autocrlf` is true, it means that the platform wants
CRLF line endings for files in the working tree, and you want to
convert them back to the normal LF line endings when checking
in to the repository.

When `core.autocrlf` is set to "input", line endings are
converted to LF upon checkin, but there is no conversion done
upon checkout.


`ident`
^^^^^^^

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


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

In the check-in codepath, the worktree file is first converted
with `ident` (if specified), and then with `crlf` (again, if
specified and applicable).

In the check-out codepath, the blob content is first converted
with `crlf`, and then `ident`.


`filter`
^^^^^^^^

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

A filter driver consists of `clean` command and `smudge`
command, either of which can be left unspecified.  Upon
checkout, when `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, `clean` command
is used to convert the contents of worktree file upon checkin.

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 keyword here is "more convenient" and not
"turning something unusable into usable".  In other words, it is
"hanging yourself because we gave you a long rope" if your
project uses filtering mechanism in such a way that it makes
your project unusable unless the checkout is done with a
specific filter in effect.


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 `crlf` (again, if specified
and applicable).

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


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

The attribute `diff` affects if `git diff` generates textual
patch for the path or just says `Binary files differ`.  It also
can affect what line is shown on the hunk header `@@ -k,l +n,m @@`
line.

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`.

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 custom diff driver.
        The driver program is given its input using the same
        calling convention as used for GIT_EXTERNAL_DIFF
        program.  This name is also used for custom hunk header
        selection.


Defining a custom 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 a custom 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 gitlink:git[7] for details.


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

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

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

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

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

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

Then, you would define "diff.tex.funcname" configuration to
specify a regular expression that matches a line that you would
want to appear as the hunk header, like this:

------------------------
[diff "tex"]
        funcname = "^\\(\\\\\\(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 occurences 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`).  Another built-in
pattern is defined for `java` that defines a pattern suitable
for program text in Java language.


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

The attribute `merge` affects how three versions of a file is
merged when a file-level merge is necessary during `git merge`,
and other programs 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 does
        not have a well-defined merge semantics.

Unspecified::

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


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

The definition of a merge 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 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.

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.


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
   diretory 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/gitattributes`.  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 assignement 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 gitlink:git[7] suite