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![Steffen Prohaska](/assets/img/avatar_default.png)
CRLF conversion bears a slight chance of corrupting data. autocrlf=true will convert CRLF to LF during commit and LF to CRLF during checkout. A file that contains a mixture of LF and CRLF before the commit cannot be recreated by git. For text files this is the right thing to do: it corrects line endings such that we have only LF line endings in the repository. But for binary files that are accidentally classified as text the conversion can corrupt data. If you recognize such corruption early you can easily fix it by setting the conversion type explicitly in .gitattributes. Right after committing you still have the original file in your work tree and this file is not yet corrupted. You can explicitly tell git that this file is binary and git will handle the file appropriately. Unfortunately, the desired effect of cleaning up text files with mixed line endings and the undesired effect of corrupting binary files cannot be distinguished. In both cases CRLFs are removed in an irreversible way. For text files this is the right thing to do because CRLFs are line endings, while for binary files converting CRLFs corrupts data. This patch adds a mechanism that can either warn the user about an irreversible conversion or can even refuse to convert. The mechanism is controlled by the variable core.safecrlf, with the following values: - false: disable safecrlf mechanism - warn: warn about irreversible conversions - true: refuse irreversible conversions The default is to warn. Users are only affected by this default if core.autocrlf is set. But the current default of git is to leave core.autocrlf unset, so users will not see warnings unless they deliberately chose to activate the autocrlf mechanism. The safecrlf mechanism's details depend on the git command. The general principles when safecrlf is active (not false) are: - we warn/error out if files in the work tree can modified in an irreversible way without giving the user a chance to backup the original file. - for read-only operations that do not modify files in the work tree we do not not print annoying warnings. There are 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. The concept of a safety check was originally proposed in a similar way by Linus Torvalds. Thanks to Dimitry Potapov for insisting on getting the naked LF/autocrlf=true case right. Signed-off-by: Steffen Prohaska <prohaska@zib.de>
515 lines
16 KiB
Plaintext
515 lines
16 KiB
Plaintext
gitattributes(5)
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================
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NAME
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----
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gitattributes - defining attributes per path
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SYNOPSIS
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--------
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$GIT_DIR/info/attributes, gitattributes
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DESCRIPTION
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-----------
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A `gitattributes` file is a simple text file that gives
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`attributes` to pathnames.
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Each line in `gitattributes` file is of form:
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glob attr1 attr2 ...
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That is, a glob pattern followed by an attributes list,
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separated by whitespaces. When the glob pattern matches the
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path in question, the attributes listed on the line are given to
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the path.
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Each attribute can be in one of these states for a given path:
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Set::
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The path has the attribute with special value "true";
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this is specified by listing only the name of the
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attribute in the attribute list.
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Unset::
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The path has the attribute with special value "false";
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this is specified by listing the name of the attribute
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prefixed with a dash `-` in the attribute list.
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Set to a value::
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The path has the attribute with specified string value;
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this is specified by listing the name of the attribute
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followed by an equal sign `=` and its value in the
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attribute list.
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Unspecified::
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No glob pattern matches the path, and nothing says if
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the path has or does not have the attribute, the
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attribute for the path is said to be Unspecified.
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When more than one glob pattern matches the path, a later line
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overrides an earlier line. This overriding is done per
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attribute.
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When deciding what attributes are assigned to a path, git
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consults `$GIT_DIR/info/attributes` file (which has the highest
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precedence), `.gitattributes` file in the same directory as the
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path in question, and its parent directories (the further the
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directory that contains `.gitattributes` is from the path in
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question, the lower its precedence).
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Sometimes you would need to override an setting of an attribute
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for a path to `unspecified` state. This can be done by listing
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the name of the attribute prefixed with an exclamation point `!`.
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EFFECTS
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-------
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Certain operations by git can be influenced by assigning
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particular attributes to a path. Currently, the following
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operations are attributes-aware.
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Checking-out and checking-in
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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These attributes affect how the contents stored in the
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repository are copied to the working tree files when commands
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such as `git checkout` and `git merge` run. They also affect how
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git stores the contents you prepare in the working tree in the
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repository upon `git add` and `git commit`.
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`crlf`
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^^^^^^
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This attribute controls the line-ending convention.
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Set::
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Setting the `crlf` attribute on a path is meant to mark
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the path as a "text" file. 'core.autocrlf' conversion
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takes place without guessing the content type by
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inspection.
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Unset::
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Unsetting the `crlf` attribute on a path is meant to
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mark the path as a "binary" file. The path never goes
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through line endings conversion upon checkin/checkout.
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Unspecified::
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Unspecified `crlf` attribute tells git to apply the
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`core.autocrlf` conversion when the file content looks
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like text.
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Set to string value "input"::
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This is similar to setting the attribute to `true`, but
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also forces git to act as if `core.autocrlf` is set to
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`input` for the path.
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Any other value set to `crlf` attribute is ignored and git acts
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as if the attribute is left unspecified.
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The `core.autocrlf` conversion
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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If the configuration variable `core.autocrlf` is false, no
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conversion is done.
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When `core.autocrlf` is true, it means that the platform wants
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CRLF line endings for files in the working tree, and you want to
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convert them back to the normal LF line endings when checking
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in to the repository.
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When `core.autocrlf` is set to "input", line endings are
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converted to LF upon checkin, but there is no conversion done
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upon checkout.
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If `core.safecrlf` is set to "true" or "warn", git verifies if
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the conversion is reversible for the current setting of
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`core.autocrlf`. For "true", git rejects irreversible
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conversions; for "warn", git only prints a warning but accepts
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an irreversible conversion. The safety triggers to prevent such
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a conversion done to the files in the work tree, but there are a
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few exceptions. Even though...
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- "git add" itself does not touch the files in the work tree, the
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next checkout would, so the safety triggers;
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- "git apply" to update a text file with a patch does touch the files
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in the work tree, but the operation is about text files and CRLF
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conversion is about fixing the line ending inconsistencies, so the
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safety does not trigger;
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- "git diff" itself does not touch the files in the work tree, it is
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often run to inspect the changes you intend to next "git add". To
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catch potential problems early, safety triggers.
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`ident`
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^^^^^^^
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When the attribute `ident` is set to a path, git replaces
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`$Id$` in the blob object with `$Id:`, followed by
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40-character hexadecimal blob object name, followed by a dollar
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sign `$` upon checkout. Any byte sequence that begins with
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`$Id:` and ends with `$` in the worktree file is replaced
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with `$Id$` upon check-in.
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`filter`
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^^^^^^^^
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A `filter` attribute can be set to a string value that names a
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filter driver specified in the configuration.
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A filter driver consists of a `clean` command and a `smudge`
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command, either of which can be left unspecified. Upon
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checkout, when the `smudge` command is specified, the command is
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fed the blob object from its standard input, and its standard
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output is used to update the worktree file. Similarly, the
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`clean` command is used to convert the contents of worktree file
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upon checkin.
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A missing filter driver definition in the config is not an error
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but makes the filter a no-op passthru.
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The content filtering is done to massage the content into a
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shape that is more convenient for the platform, filesystem, and
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the user to use. The key phrase here is "more convenient" and not
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"turning something unusable into usable". In other words, the
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intent is that if someone unsets the filter driver definition,
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or does not have the appropriate filter program, the project
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should still be usable.
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Interaction between checkin/checkout attributes
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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In the check-in codepath, the worktree file is first converted
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with `filter` driver (if specified and corresponding driver
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defined), then the result is processed with `ident` (if
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specified), and then finally with `crlf` (again, if specified
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and applicable).
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In the check-out codepath, the blob content is first converted
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with `crlf`, and then `ident` and fed to `filter`.
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Generating diff text
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~~~~~~~~~~~~~~~~~~~~
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The attribute `diff` affects if `git diff` generates textual
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patch for the path or just says `Binary files differ`. It also
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can affect what line is shown on the hunk header `@@ -k,l +n,m @@`
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line.
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Set::
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A path to which the `diff` attribute is set is treated
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as text, even when they contain byte values that
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normally never appear in text files, such as NUL.
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Unset::
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A path to which the `diff` attribute is unset will
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generate `Binary files differ`.
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Unspecified::
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A path to which the `diff` attribute is unspecified
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first gets its contents inspected, and if it looks like
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text, it is treated as text. Otherwise it would
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generate `Binary files differ`.
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String::
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Diff is shown using the specified custom diff driver.
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The driver program is given its input using the same
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calling convention as used for GIT_EXTERNAL_DIFF
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program. This name is also used for custom hunk header
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selection.
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Defining a custom diff driver
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The definition of a diff driver is done in `gitconfig`, not
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`gitattributes` file, so strictly speaking this manual page is a
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wrong place to talk about it. However...
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To define a custom diff driver `jcdiff`, add a section to your
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`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
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----------------------------------------------------------------
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[diff "jcdiff"]
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command = j-c-diff
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----------------------------------------------------------------
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When git needs to show you a diff for the path with `diff`
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attribute set to `jcdiff`, it calls the command you specified
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with the above configuration, i.e. `j-c-diff`, with 7
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parameters, just like `GIT_EXTERNAL_DIFF` program is called.
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See linkgit:git[7] for details.
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Defining a custom hunk-header
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Each group of changes (called "hunk") in the textual diff output
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is prefixed with a line of the form:
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@@ -k,l +n,m @@ TEXT
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The text is called 'hunk header', and by default a line that
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begins with an alphabet, an underscore or a dollar sign is used,
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which matches what GNU `diff -p` output uses. This default
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selection however is not suited for some contents, and you can
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use customized pattern to make a selection.
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First in .gitattributes, you would assign the `diff` attribute
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for paths.
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------------------------
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*.tex diff=tex
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------------------------
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Then, you would define "diff.tex.funcname" configuration to
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specify a regular expression that matches a line that you would
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want to appear as the hunk header, like this:
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------------------------
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[diff "tex"]
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funcname = "^\\(\\\\\\(sub\\)*section{.*\\)$"
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------------------------
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Note. A single level of backslashes are eaten by the
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configuration file parser, so you would need to double the
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backslashes; the pattern above picks a line that begins with a
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backslash, and zero or more occurrences of `sub` followed by
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`section` followed by open brace, to the end of line.
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There are a few built-in patterns to make this easier, and `tex`
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is one of them, so you do not have to write the above in your
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configuration file (you still need to enable this with the
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attribute mechanism, via `.gitattributes`). Another built-in
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pattern is defined for `java` that defines a pattern suitable
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for program text in Java language.
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Performing a three-way merge
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The attribute `merge` affects how three versions of a file is
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merged when a file-level merge is necessary during `git merge`,
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and other programs such as `git revert` and `git cherry-pick`.
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Set::
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Built-in 3-way merge driver is used to merge the
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contents in a way similar to `merge` command of `RCS`
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suite. This is suitable for ordinary text files.
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Unset::
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Take the version from the current branch as the
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tentative merge result, and declare that the merge has
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conflicts. This is suitable for binary files that does
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not have a well-defined merge semantics.
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Unspecified::
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By default, this uses the same built-in 3-way merge
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driver as is the case the `merge` attribute is set.
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However, `merge.default` configuration variable can name
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different merge driver to be used for paths to which the
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`merge` attribute is unspecified.
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String::
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3-way merge is performed using the specified custom
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merge driver. The built-in 3-way merge driver can be
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explicitly specified by asking for "text" driver; the
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built-in "take the current branch" driver can be
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requested with "binary".
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Built-in merge drivers
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^^^^^^^^^^^^^^^^^^^^^^
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There are a few built-in low-level merge drivers defined that
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can be asked for via the `merge` attribute.
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text::
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Usual 3-way file level merge for text files. Conflicted
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regions are marked with conflict markers `<<<<<<<`,
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`=======` and `>>>>>>>`. The version from your branch
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appears before the `=======` marker, and the version
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from the merged branch appears after the `=======`
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marker.
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binary::
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Keep the version from your branch in the work tree, but
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leave the path in the conflicted state for the user to
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sort out.
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union::
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Run 3-way file level merge for text files, but take
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lines from both versions, instead of leaving conflict
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markers. This tends to leave the added lines in the
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resulting file in random order and the user should
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verify the result. Do not use this if you do not
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understand the implications.
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Defining a custom merge driver
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The definition of a merge driver is done in the `.git/config`
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file, not in the `gitattributes` file, so strictly speaking this
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manual page is a wrong place to talk about it. However...
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To define a custom merge driver `filfre`, add a section to your
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`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
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----------------------------------------------------------------
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[merge "filfre"]
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name = feel-free merge driver
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driver = filfre %O %A %B
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recursive = binary
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----------------------------------------------------------------
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The `merge.*.name` variable gives the driver a human-readable
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name.
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The `merge.*.driver` variable's value is used to construct a
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command to run to merge ancestor's version (`%O`), current
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version (`%A`) and the other branches' version (`%B`). These
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three tokens are replaced with the names of temporary files that
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hold the contents of these versions when the command line is
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built.
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The merge driver is expected to leave the result of the merge in
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the file named with `%A` by overwriting it, and exit with zero
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status if it managed to merge them cleanly, or non-zero if there
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were conflicts.
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The `merge.*.recursive` variable specifies what other merge
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driver to use when the merge driver is called for an internal
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merge between common ancestors, when there are more than one.
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When left unspecified, the driver itself is used for both
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internal merge and the final merge.
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Checking whitespace errors
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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`whitespace`
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^^^^^^^^^^^^
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The `core.whitespace` configuration variable allows you to define what
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`diff` and `apply` should consider whitespace errors for all paths in
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the project (See linkgit:git-config[1]). This attribute gives you finer
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control per path.
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Set::
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Notice all types of potential whitespace errors known to git.
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Unset::
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Do not notice anything as error.
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Unspecified::
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Use the value of `core.whitespace` configuration variable to
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decide what to notice as error.
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String::
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Specify a comma separate list of common whitespace problems to
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notice in the same format as `core.whitespace` configuration
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variable.
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EXAMPLE
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-------
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If you have these three `gitattributes` file:
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----------------------------------------------------------------
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(in $GIT_DIR/info/attributes)
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a* foo !bar -baz
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(in .gitattributes)
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abc foo bar baz
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(in t/.gitattributes)
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ab* merge=filfre
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abc -foo -bar
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*.c frotz
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----------------------------------------------------------------
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the attributes given to path `t/abc` are computed as follows:
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1. By examining `t/.gitattributes` (which is in the same
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directory as the path in question), git finds that the first
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line matches. `merge` attribute is set. It also finds that
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the second line matches, and attributes `foo` and `bar`
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are unset.
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2. Then it examines `.gitattributes` (which is in the parent
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directory), and finds that the first line matches, but
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`t/.gitattributes` file already decided how `merge`, `foo`
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and `bar` attributes should be given to this path, so it
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leaves `foo` and `bar` unset. Attribute `baz` is set.
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3. Finally it examines `$GIT_DIR/info/attributes`. This file
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is used to override the in-tree settings. The first line is
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a match, and `foo` is set, `bar` is reverted to unspecified
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state, and `baz` is unset.
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As the result, the attributes assignment to `t/abc` becomes:
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----------------------------------------------------------------
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foo set to true
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bar unspecified
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baz set to false
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merge set to string value "filfre"
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frotz unspecified
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----------------------------------------------------------------
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Creating an archive
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~~~~~~~~~~~~~~~~~~~
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`export-subst`
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^^^^^^^^^^^^^^
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If the attribute `export-subst` is set for a file then git will expand
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several placeholders when adding this file to an archive. The
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expansion depends on the availability of a commit ID, i.e. if
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linkgit:git-archive[1] has been given a tree instead of a commit or a
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tag then no replacement will be done. The placeholders are the same
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as those for the option `--pretty=format:` of linkgit:git-log[1],
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except that they need to be wrapped like this: `$Format:PLACEHOLDERS$`
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in the file. E.g. the string `$Format:%H$` will be replaced by the
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commit hash.
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GIT
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---
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Part of the linkgit:git[7] suite
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