git-annex/doc/tips/largefiles.mdwn

[[!meta title="annex.largefiles: configuring mixed content repositories"]]

Normally commands like `git annex add` always add files to the annex.
And when using the v7 repository mode, even `git add` and `git commit -a`
will add files to the annex.

Let's suppose you're developing a video game, written in C. You have
source code, and some large game assets. You want to ensure the source
code is stored in git -- that's what git's for! And you want to store
the game assets in the git annex -- to avod bloating your git repos with
possibly enormous files, but still version control them.

The annex.largefiles configuration is useful for such mixed content
repositories. It's checked by `git annex add`, by `git add` and `git commit -a`
(in v7 repositories), by `git annex import` and the assistant. It's
also used by `git annex addurl` and `git annex importfeed` when downloading
files. When a file does not match annex.largefiles, these commands will
add its content to git instead of to the annex.

This saves you the bother of keeping things straight when adding files.

## examples

For example, let's make only files larger than 100 kb be added to the annex,
and never `*.c` and `*.h` source code files.

Write this to the `.gitattributes` file:

	* annex.largefiles=(largerthan=100kb)
	*.c annex.largefiles=nothing
	*.h annex.largefiles=nothing

Or, set the git configuration instead:
  
	git config annex.largefiles 'largerthan=100kb and not (include=*.c or include=*.h)'

Both of these settings do the same thing. Setting it in the `.gitattributes`
file makes any checkout of the repository share that configuration, so is often
a good choice. Setting the annex.largefiles git configuration lets different
checkouts behave differently. The git configuration overrides the
`.gitattributes` configuration.

## syntax

The value of annex.largefiles is similar to a
[[preferred content expression|git-annex-preferred-content]].
The following terms can be used in annex.largefiles:

* `include=glob` / `exclude=glob`

  Specify files to include or exclude.

  The glob can contain `*` and `?` to match arbitrary characters.

* `smallerthan=size` / `largerthan=size`

  Matches only files smaller than, or larger than the specified size.

  The size can be specified with any commonly used units, for example,
  "0.5 gb" or "100 KiloBytes"

* `mimetype=glob`

  Looks up the MIME type of a file, and checks if the glob matches it.

  For example, `"mimetype=text/*"` will match many varieties of text files,
  including "text/plain", but also "text/x-shellscript", "text/x-makefile",
  etc.

  The MIME types are the same that are displayed by running `file --mime-type`

  This is only available to use when git-annex was built with the
  MagicMime build flag.

* `mimeencoding=glob`

  Looks up the MIME encoding of a file, and checks if the glob matches it.

  For example, `"mimeencoding=binary"` will match many kinds of binary
  files.

  The MIME encodings are the same that are displayed by running `file --mime-encoding`

  This is only available to use when git-annex was built with the
  MagicMime build flag.

* `anything`

  Matches any file.

* `nothing`

  Matches no files. (Same as "not anything")

* `not expression`

  Inverts what the expression matches.

* `and` / `or` / `( expression )`

  These can be used to build up more complicated expressions.

The way the `.gitattributes` example above works is, `*.c` and `*.h` files
have the annex.largefiles attribute set to "nothing",
and so those files are never treated as large files. All other files use
the other value, which checks the file size.

Note that, since git attribute values cannot contain whitespace,
it's useful to instead parenthesize the terms of the annex.largefiles
attribute. This trick allows for more complicated expressions.
For example, this is the same as the git config shown earlier, shoehorned
into a git attribute:

	* annex.largefiles=(largerthan=100kb)and(not((include=*.c)or(include=*.h)))

## temporarily override

If you've set up an annex.largefiles configuration but want to force a file to
be stored in the annex, you can temporarily override the configuration like
this:

	git annex add -c annex.largefiles=anything smallfile

## converting git to annexed

When you have a file that is currently stored in git, and you want to
convert that to be stored in the annex, here's how to accomplish that:

	git rm --cached file
	git annex add -c annex.largefiles=anything file
	git commit file

This first removes the file from git's index cache, and then adds it back
using git-annex. You can modify the file before the `git-annex add` step,
perhaps replacing it with new larger content that necessitates git-annex.

## converting annexed to git

When you have a file that is currently stored in the annex, and you want to
convert that to be stored in git, here's how to accomplish that:

	git annex unlock file
	git -c annex.largefiles=nothing add file
	git commit -n file

You can modify the file after unlocking it and before adding it to
git. And this is probably a good idea if it was really a big file,
so that you can replace its content with something smaller.

Notice the `-n` switch when committing the file. This bypasses the
[[git-annex-precommit]] hook. In this situation, that hook sees an unlocked
file and wants to add it back to the annex, so you have to bypass the hook
to get the file committed to git.