Merge branch 'jh/fsmonitor-darwin-modernize'

[thirdparty/git.git] / Documentation / git-sparse-checkout.txt

git-sparse-checkout(1)
======================

NAME
----
git-sparse-checkout - Reduce your working tree to a subset of tracked files


SYNOPSIS
--------
[verse]
'git sparse-checkout' (init | list | set | add | reapply | disable) [<options>]


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

This command is used to create sparse checkouts, which change the
working tree from having all tracked files present to only having a
subset of those files.  It can also switch which subset of files are
present, or undo and go back to having all tracked files present in
the working copy.

The subset of files is chosen by providing a list of directories in
cone mode (the default), or by providing a list of patterns in
non-cone mode.

When in a sparse-checkout, other Git commands behave a bit differently.
For example, switching branches will not update paths outside the
sparse-checkout directories/patterns, and `git commit -a` will not record
paths outside the sparse-checkout directories/patterns as deleted.

THIS COMMAND IS EXPERIMENTAL. ITS BEHAVIOR, AND THE BEHAVIOR OF OTHER
COMMANDS IN THE PRESENCE OF SPARSE-CHECKOUTS, WILL LIKELY CHANGE IN
THE FUTURE.


COMMANDS
--------
'list'::
        Describe the directories or patterns in the sparse-checkout file.

'set'::
        Enable the necessary sparse-checkout config settings
        (`core.sparseCheckout`, `core.sparseCheckoutCone`, and
        `index.sparse`) if they are not already set to the desired values,
        populate the sparse-checkout file from the list of arguments
        following the 'set' subcommand, and update the working directory to
        match.
+
To ensure that adjusting the sparse-checkout settings within a worktree
does not alter the sparse-checkout settings in other worktrees, the 'set'
subcommand will upgrade your repository config to use worktree-specific
config if not already present. The sparsity defined by the arguments to
the 'set' subcommand are stored in the worktree-specific sparse-checkout
file. See linkgit:git-worktree[1] and the documentation of
`extensions.worktreeConfig` in linkgit:git-config[1] for more details.
+
When the `--stdin` option is provided, the directories or patterns are
read from standard in as a newline-delimited list instead of from the
arguments.
+
By default, the input list is considered a list of directories, matching
the output of `git ls-tree -d --name-only`.  This includes interpreting
pathnames that begin with a double quote (") as C-style quoted strings.
Note that all files under the specified directories (at any depth) will
be included in the sparse checkout, as well as files that are siblings
of either the given directory or any of its ancestors (see 'CONE PATTERN
SET' below for more details).  In the past, this was not the default,
and `--cone` needed to be specified or `core.sparseCheckoutCone` needed
to be enabled.
+
When `--no-cone` is passed, the input list is considered a list of
patterns.  This mode has a number of drawbacks, including not working
with some options like `--sparse-index`.  As explained in the
"Non-cone Problems" section below, we do not recommend using it.
+
Use the `--[no-]sparse-index` option to use a sparse index (the
default is to not use it).  A sparse index reduces the size of the
index to be more closely aligned with your sparse-checkout
definition. This can have significant performance advantages for
commands such as `git status` or `git add`.  This feature is still
experimental. Some commands might be slower with a sparse index until
they are properly integrated with the feature.
+
**WARNING:** Using a sparse index requires modifying the index in a way
that is not completely understood by external tools. If you have trouble
with this compatibility, then run `git sparse-checkout init --no-sparse-index`
to rewrite your index to not be sparse. Older versions of Git will not
understand the sparse directory entries index extension and may fail to
interact with your repository until it is disabled.

'add'::
        Update the sparse-checkout file to include additional directories
        (in cone mode) or patterns (in non-cone mode).  By default, these
        directories or patterns are read from the command-line arguments,
        but they can be read from stdin using the `--stdin` option.

'reapply'::
        Reapply the sparsity pattern rules to paths in the working tree.
        Commands like merge or rebase can materialize paths to do their
        work (e.g. in order to show you a conflict), and other
        sparse-checkout commands might fail to sparsify an individual file
        (e.g. because it has unstaged changes or conflicts).  In such
        cases, it can make sense to run `git sparse-checkout reapply` later
        after cleaning up affected paths (e.g. resolving conflicts, undoing
        or committing changes, etc.).
+
The `reapply` command can also take `--[no-]cone` and `--[no-]sparse-index`
flags, with the same meaning as the flags from the `set` command, in order
to change which sparsity mode you are using without needing to also respecify
all sparsity paths.

'disable'::
        Disable the `core.sparseCheckout` config setting, and restore the
        working directory to include all files.

'init'::
        Deprecated command that behaves like `set` with no specified paths.
        May be removed in the future.
+
Historically, `set` did not handle all the necessary config settings,
which meant that both `init` and `set` had to be called.  Invoking
both meant the `init` step would first remove nearly all tracked files
(and in cone mode, ignored files too), then the `set` step would add
many of the tracked files (but not ignored files) back.  In addition
to the lost files, the performance and UI of this combination was
poor.
+
Also, historically, `init` would not actually initialize the
sparse-checkout file if it already existed.  This meant it was
possible to return to a sparse-checkout without remembering which
paths to pass to a subsequent 'set' or 'add' command.  However,
`--cone` and `--sparse-index` options would not be remembered across
the disable command, so the easy restore of calling a plain `init`
decreased in utility.

EXAMPLES
--------
`git sparse-checkout set MY/DIR1 SUB/DIR2`::

        Change to a sparse checkout with all files (at any depth) under
        MY/DIR1/ and SUB/DIR2/ present in the working copy (plus all
        files immediately under MY/ and SUB/ and the toplevel
        directory).  If already in a sparse checkout, change which files
        are present in the working copy to this new selection.  Note
        that this command will also delete all ignored files in any
        directory that no longer has either tracked or
        non-ignored-untracked files present.

`git sparse-checkout disable`::

        Repopulate the working directory with all files, disabling sparse
        checkouts.

`git sparse-checkout add SOME/DIR/ECTORY`::

        Add all files under SOME/DIR/ECTORY/ (at any depth) to the
        sparse checkout, as well as all files immediately under
        SOME/DIR/ and immediately under SOME/.  Must already be in a
        sparse checkout before using this command.

`git sparse-checkout reapply`::

        It is possible for commands to update the working tree in a
        way that does not respect the selected sparsity directories.
        This can come from tools external to Git writing files, or
        even affect Git commands because of either special cases (such
        as hitting conflicts when merging/rebasing), or because some
        commands didn't fully support sparse checkouts (e.g. the old
        `recursive` merge backend had only limited support).  This
        command reapplies the existing sparse directory specifications
        to make the working directory match.

INTERNALS -- SPARSE CHECKOUT
----------------------------

"Sparse checkout" allows populating the working directory sparsely.  It
uses the skip-worktree bit (see linkgit:git-update-index[1]) to tell Git
whether a file in the working directory is worth looking at. If the
skip-worktree bit is set, and the file is not present in the working tree,
then its absence is ignored. Git will avoid populating the contents of
those files, which makes a sparse checkout helpful when working in a
repository with many files, but only a few are important to the current
user.

The `$GIT_DIR/info/sparse-checkout` file is used to define the
skip-worktree reference bitmap. When Git updates the working
directory, it updates the skip-worktree bits in the index based
on this file. The files matching the patterns in the file will
appear in the working directory, and the rest will not.

INTERNALS -- NON-CONE PROBLEMS
------------------------------

The `$GIT_DIR/info/sparse-checkout` file populated by the `set` and
`add` subcommands is defined to be a bunch of patterns (one per line)
using the same syntax as `.gitignore` files.  In cone mode, these
patterns are restricted to matching directories (and users only ever
need supply or see directory names), while in non-cone mode any
gitignore-style pattern is permitted.  Using the full gitignore-style
patterns in non-cone mode has a number of shortcomings:

  * Fundamentally, it makes various worktree-updating processes (pull,
    merge, rebase, switch, reset, checkout, etc.) require O(N*M) pattern
    matches, where N is the number of patterns and M is the number of
    paths in the index.  This scales poorly.

  * Avoiding the scaling issue has to be done via limiting the number
    of patterns via specifying leading directory name or glob.

  * Passing globs on the command line is error-prone as users may
    forget to quote the glob, causing the shell to expand it into all
    matching files and pass them all individually along to
    sparse-checkout set/add.  While this could also be a problem with
    e.g. "git grep -- *.c", mistakes with grep/log/status appear in
    the immediate output.  With sparse-checkout, the mistake gets
    recorded at the time the sparse-checkout command is run and might
    not be problematic until the user later switches branches or rebases
    or merges, thus putting a delay between the user's error and when
    they have a chance to catch/notice it.

  * Related to the previous item, sparse-checkout has an 'add'
    subcommand but no 'remove' subcommand.  Even if a 'remove'
    subcommand were added, undoing an accidental unquoted glob runs
    the risk of "removing too much", as it may remove entries that had
    been included before the accidental add.

  * Non-cone mode uses gitignore-style patterns to select what to
    *include* (with the exception of negated patterns), while
    .gitignore files use gitignore-style patterns to select what to
    *exclude* (with the exception of negated patterns).  The
    documentation on gitignore-style patterns usually does not talk in
    terms of matching or non-matching, but on what the user wants to
    "exclude".  This can cause confusion for users trying to learn how
    to specify sparse-checkout patterns to get their desired behavior.

  * Every other git subcommand that wants to provide "special path
    pattern matching" of some sort uses pathspecs, but non-cone mode
    for sparse-checkout uses gitignore patterns, which feels
    inconsistent.

  * It has edge cases where the "right" behavior is unclear.  Two examples:

    First, two users are in a subdirectory, and the first runs
       git sparse-checkout set '/toplevel-dir/*.c'
    while the second runs
       git sparse-checkout set relative-dir
    Should those arguments be transliterated into
       current/subdirectory/toplevel-dir/*.c
    and
       current/subdirectory/relative-dir
    before inserting into the sparse-checkout file?  The user who typed
    the first command is probably aware that arguments to set/add are
    supposed to be patterns in non-cone mode, and probably would not be
    happy with such a transliteration.  However, many gitignore-style
    patterns are just paths, which might be what the user who typed the
    second command was thinking, and they'd be upset if their argument
    wasn't transliterated.

    Second, what should bash-completion complete on for set/add commands
    for non-cone users?  If it suggests paths, is it exacerbating the
    problem above?  Also, if it suggests paths, what if the user has a
    file or directory that begins with either a '!' or '#' or has a '*',
    '\', '?', '[', or ']' in its name?  And if it suggests paths, will
    it complete "/pro" to "/proc" (in the root filesytem) rather than to
    "/progress.txt" in the current directory?  (Note that users are
    likely to want to start paths with a leading '/' in non-cone mode,
    for the same reason that .gitignore files often have one.)
    Completing on files or directories might give nasty surprises in
    all these cases.

  * The excessive flexibility made other extensions essentially
    impractical.  `--sparse-index` is likely impossible in non-cone
    mode; even if it is somehow feasible, it would have been far more
    work to implement and may have been too slow in practice.  Some
    ideas for adding coupling between partial clones and sparse
    checkouts are only practical with a more restricted set of paths
    as well.

For all these reasons, non-cone mode is deprecated.  Please switch to
using cone mode.


INTERNALS -- CONE MODE HANDLING
-------------------------------

The "cone mode", which is the default, lets you specify only what
directories to include.  For any directory specified, all paths below
that directory will be included, and any paths immediately under
leading directories (including the toplevel directory) will also be
included.  Thus, if you specified the directory
    Documentation/technical/
then your sparse checkout would contain:

  * all files in the toplevel-directory
  * all files immediately under Documentation/
  * all files at any depth under Documentation/technical/

Also, in cone mode, even if no directories are specified, then the
files in the toplevel directory will be included.

When changing the sparse-checkout patterns in cone mode, Git will inspect each
tracked directory that is not within the sparse-checkout cone to see if it
contains any untracked files. If all of those files are ignored due to the
`.gitignore` patterns, then the directory will be deleted. If any of the
untracked files within that directory is not ignored, then no deletions will
occur within that directory and a warning message will appear. If these files
are important, then reset your sparse-checkout definition so they are included,
use `git add` and `git commit` to store them, then remove any remaining files
manually to ensure Git can behave optimally.

See also the "Internals -- Cone Pattern Set" section to learn how the
directories are transformed under the hood into a subset of the
Full Pattern Set of sparse-checkout.


INTERNALS -- FULL PATTERN SET
-----------------------------

The full pattern set allows for arbitrary pattern matches and complicated
inclusion/exclusion rules. These can result in O(N*M) pattern matches when
updating the index, where N is the number of patterns and M is the number
of paths in the index. To combat this performance issue, a more restricted
pattern set is allowed when `core.sparseCheckoutCone` is enabled.

The sparse-checkout file uses the same syntax as `.gitignore` files;
see linkgit:gitignore[5] for details.  Here, though, the patterns are
usually being used to select which files to include rather than which
files to exclude.  (However, it can get a bit confusing since
gitignore-style patterns have negations defined by patterns which
begin with a '!', so you can also select files to _not_ include.)

For example, to select everything, and then to remove the file
`unwanted` (so that every file will appear in your working tree except
the file named `unwanted`):

    git sparse-checkout set --no-cone '/*' '!unwanted'

These patterns are just placed into the
`$GIT_DIR/info/sparse-checkout` as-is, so the contents of that file
at this point would be

----------------
/*
!unwanted
----------------

See also the "Sparse Checkout" section of linkgit:git-read-tree[1] to
learn more about the gitignore-style patterns used in sparse
checkouts.


INTERNALS -- CONE PATTERN SET
-----------------------------

In cone mode, only directories are accepted, but they are translated into
the same gitignore-style patterns used in the full pattern set.  We refer
to the particular patterns used in those mode as being of one of two types:

1. *Recursive:* All paths inside a directory are included.

2. *Parent:* All files immediately inside a directory are included.

Since cone mode always includes files at the toplevel, when running
`git sparse-checkout set` with no directories specified, the toplevel
directory is added as a parent pattern.  At this point, the
sparse-checkout file contains the following patterns:

----------------
/*
!/*/
----------------

This says "include everything immediately under the toplevel
directory, but nothing at any level below that."

When in cone mode, the `git sparse-checkout set` subcommand takes a
list of directories.  The command `git sparse-checkout set A/B/C` sets
the directory `A/B/C` as a recursive pattern, the directories `A` and
`A/B` are added as parent patterns. The resulting sparse-checkout file
is now

----------------
/*
!/*/
/A/
!/A/*/
/A/B/
!/A/B/*/
/A/B/C/
----------------

Here, order matters, so the negative patterns are overridden by the positive
patterns that appear lower in the file.

Unless `core.sparseCheckoutCone` is explicitly set to `false`, Git will
parse the sparse-checkout file expecting patterns of these types. Git will
warn if the patterns do not match.  If the patterns do match the expected
format, then Git will use faster hash-based algorithms to compute inclusion
in the sparse-checkout.  If they do not match, git will behave as though
`core.sparseCheckoutCone` was false, regardless of its setting.

In the cone mode case, despite the fact that full patterns are written
to the $GIT_DIR/info/sparse-checkout file, the `git sparse-checkout
list` subcommand will list the directories that define the recursive
patterns. For the example sparse-checkout file above, the output is as
follows:

--------------------------
$ git sparse-checkout list
A/B/C
--------------------------

If `core.ignoreCase=true`, then the pattern-matching algorithm will use a
case-insensitive check. This corrects for case mismatched filenames in the
'git sparse-checkout set' command to reflect the expected cone in the working
directory.


INTERNALS -- SUBMODULES
-----------------------

If your repository contains one or more submodules, then submodules
are populated based on interactions with the `git submodule` command.
Specifically, `git submodule init -- <path>` will ensure the submodule
at `<path>` is present, while `git submodule deinit [-f] -- <path>`
will remove the files for the submodule at `<path>` (including any
untracked files, uncommitted changes, and unpushed history).  Similar
to how sparse-checkout removes files from the working tree but still
leaves entries in the index, deinitialized submodules are removed from
the working directory but still have an entry in the index.

Since submodules may have unpushed changes or untracked files,
removing them could result in data loss.  Thus, changing sparse
inclusion/exclusion rules will not cause an already checked out
submodule to be removed from the working copy.  Said another way, just
as `checkout` will not cause submodules to be automatically removed or
initialized even when switching between branches that remove or add
submodules, using `sparse-checkout` to reduce or expand the scope of
"interesting" files will not cause submodules to be automatically
deinitialized or initialized either.

Further, the above facts mean that there are multiple reasons that
"tracked" files might not be present in the working copy: sparsity
pattern application from sparse-checkout, and submodule initialization
state.  Thus, commands like `git grep` that work on tracked files in
the working copy may return results that are limited by either or both
of these restrictions.


SEE ALSO
--------

linkgit:git-read-tree[1]
linkgit:gitignore[5]

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