peru

Maybe sometimes better than copy-paste.

Peru is a tool for including other people's code in your projects. It
fetches from anywhere -- git, hg, svn, tarballs -- and puts files
wherever you like. Peru helps you track exact versions of your
dependencies, so that your history is always reproducible. And it fits
inside your scripts and Makefiles, so your build
stays simple and foolproof.

Why?

If you build with make, you don't have to do anything special when you
switch branches or pull new commits. Build tools notice those changes
without any help. But if you depend on other people's code, the tools
aren't so automatic anymore. You need to remember when to git submodule update or go get -u or pip install -r. If you forget a step you can
break your build, or worse, you might build something wrong without
noticing.

Peru wants you to automate dependency management just like you automate
the rest of your build. It doesn't interfere with your source control or
install anything global, so you can just throw it in at the start of a
script and forget about it. It'll run every time, and your dependencies
will never be out of sync. Simple, and fast as heck.

The name "peru", along with our love for reproducible builds, was inspired by
Amazon's Brazil build system.
It also happens to be an anagram for "reup".

Installation

Peru supports Linux, Mac, and Windows. It requires python (3.5 or later)
and git, and optionally hg and svn if you want fetch from those
types of repos. Use pip to install it:

pip install peru

Note that depending on how Python is set up on your machine, you might
need to use sudo with that, and Python 3's pip might be called pip3.
Also, if you have to use Python 3.3 or 3.4, those were supported up to
peru 1.1.4.

On Ubuntu, you can install also peru from our
PPA. On Arch,
you can install peru from the
AUR.

Getting Started

Here's the peru version of the first git submodules
example
from the Git Book. We're going to add the Rack
library to our project. First, create a peru.yaml file like this:

imports:
    rack_example: rack/  # This is where we want peru to put the module.

git module rack_example:
    url: git://github.com/chneukirchen/rack.git

Now run peru sync.

What the heck just happened?

Peru cloned Rack for you, and imported a copy of it under the rack directory.
It also created a magical directory called .peru to hold that clone and some
other business. If you're using source control, now would be a good time to put
these directories in your ignore list (like .gitignore). You usually don't
want to check them in.

Running peru clean will make the imported directory disappear. Running peru sync again will make it come back, and it'll be a lot faster this time,
because peru caches everything.

Getting Fancy

For a more involved example, let's use peru to manage some dotfiles. We're big
fans of the Solarized colorscheme, and
we want to get it working in both ls and vim. For ls all we need peru to
do is fetch a Solarized dircolors file. (That'll get loaded somewhere like
.bashrc, not included in this example.) For vim we're going to need the
Solarized vim plugin,
and we also want Pathogen, which makes
plugin installation much cleaner. Here's the peru.yaml:

imports:
    # The dircolors file just goes at the root of our project.
    dircolors: ./
    # We're going to merge Pathogen's autoload directory into our own.
    pathogen: .vim/autoload/
    # The Solarized plugin gets its own directory, where Pathogen expects it.
    vim-solarized: .vim/bundle/solarized/

git module dircolors:
    url: https://github.com/seebi/dircolors-solarized
    # Only copy this file. Can be a list of files. Accepts * and ** globs.
    pick: dircolors.ansi-dark

curl module pathogen:
    url: https://codeload.github.com/tpope/vim-pathogen/tar.gz/v2.3
    # Untar the archive after fetching.
    unpack: tar
    # After the unpack, use this subdirectory as the root of the module.
    export: vim-pathogen-2.3/autoload/

git module vim-solarized:
    url: https://github.com/altercation/vim-colors-solarized
    # Fetch this exact commit, instead of master.
    rev: 7a7e5c8818d717084730133ed6b84a3ffc9d0447

The contents of the dircolors module are copied to the root of our repo. The
pick field restricts this to just one file, dircolors.ansi-dark.

The pathogen module uses the curl type instead of git, and its URL points
to a tarball. (This is for the sake of an example. In real life you'd probably
use git here too.) The unpack field means that we get the contents of the
tarball rather than the tarball file itself. Because the module specifies an
export directory, it's that directory rather than the whole module that gets
copied to the import path, .vim/autoload. The result is that Pathogen's
autoload directory gets merged with our own, which is the standard way to
install Pathogen.

The vim-solarized module gets copied into its own directory under bundle,
which is where Pathogen will look for it. Note that it has an explicit rev
field, which tells peru to fetch that exact revision, rather than the
default branch (master in git). That's a Super Serious Best Practice™,
because it means your dependencies will always be consistent, even when you
look at commits from a long time ago.

You really want all of your dependencies to have hashes, but editing
those by hand is painful. The next section is about making that easier.

Magical Updates

If you run peru reup, peru will talk to each of your upstream repos, get
their latest versions, and then edit your peru.yaml file with any updates. If
you don't have peru.yaml checked into some kind of source control, you should
probably do that first, because the reup will modify it in place. When we reup
the example above, the changes look something like this:

diff --git a/peru.yaml b/peru.yaml
index 15c758d..7f0e26b 100644
--- a/peru.yaml
+++ b/peru.yaml
@@ -6,12 +6,14 @@ imports:
 git module dircolors:
     url: https://github.com/seebi/dircolors-solarized
     pick: dircolors.ansi-dark
+    rev: a5e130c642e45323a22226f331cb60fd37ce564f

 curl module pathogen:
     url: https://codeload.github.com/tpope/vim-pathogen/tar.gz/v2.3
     unpack: tar
     export: vim-pathogen-2.3/autoload/
+    sha1: 9c3fd6d9891bfe2cd3ed3ddc9ffe5f3fccb72b6a

 git module vim-solarized:
     url: https://github.com/altercation/vim-colors-solarized
-    rev: 7a7e5c8818d717084730133ed6b84a3ffc9d0447
+    rev: 528a59f26d12278698bb946f8fb82a63711eec21

Peru made three changes:

• The dircolors module, which didn't have a rev before, just got one. By
  default for git, this is the current master. To change that, you can set
  the reup field to the name of a different branch.
• The pathogen module got a sha1 field. Unlike git, a curl module is
  plain old HTTP, so it's stuck downloading whatever file is at the url. But
  it will check this hash after the download is finished, and it will raise an
  error if there's a mismatch.
• The vim-solarized module had a hash before, but it's been updated. Again,
  the new value came from master by default.

At this point, you'll probably want to make a new commit of peru.yaml to
record the version bumps. You can do this every so often to keep your plugins
up to date, and you'll always be able to reach old versions in your history.

Commands

• sync
  • Pull in your imports. sync yells at you instead of overwriting existing
    or modified files. Use --force/-f to tell it you're serious.
• clean
  • Remove imported files. Same --force/-f flag as sync.
• reup
  • Update module fields with new revision information. For git, hg, and
    svn, this updates the rev field. For curl, this sets the sha1
    field. You can optionally give specific module names as arguments.
• copy
  • Make a copy of all the files in a module. Either specify a directory to put
    them in, or peru will create a temp dir for you. You can use this to see
    modules you don't normally import, or to play with different module/rule
    combinations (see "Rules" below).
• override
  • Replace the contents of a module with a local directory path, usually a
    clone you've made of the same repo. This lets you test changes to imported
    modules without needing to push your changes upstream or edit peru.yaml.

Module Types

git, hg, svn

For cloning repos. These types all provide the same fields:

• url: required, any protocol supported by the underlying VCS
• rev: optional, the specific revision/branch/tag to fetch
• reup: optional, the branch/tag to get the latest rev from when running
  peru reup

The git type also supports setting submodules: false to skip
fetching git submodules. Otherwise they're included by default.

curl

For downloading a file from a URL. This type is powered by Pythons's standard
library, rather than an external program.

• url: required, any kind supported by urllib (HTTP, FTP, file://)
• filename: optional, overrides the default filename
• sha1: optional, checks that the downloaded file matches the checksum
• unpack: optional, tar or zip

Peru includes a few other types mostly for testing purposes. See rsync for an
example implemented in Bash.

Creating New Module Types

Module type plugins are as-dumb-as-possible scripts that only know how to
sync, and optionally reup. Peru shells out to them and then handles most of
the caching magic itself, though plugins can also do their own caching as
appropriate. For example, the git and hg plugins keep track of repos they
clone. Peru itself doesn't need to know how to do that. For all the details,
see Architecture: Plugins.

Rules

Some fields (like rev and unpack) are specific to certain module
types. There are also fields you can use in any module, which modify the
tree of files after it's fetched. Some of these made an appearance in
the fancy example above:

• copy: A map or multimap of source and destination paths to copy.
  Works like cp on the command line, so if the destination is a
  directory, it'll preserve the source filename and copy into the
  destination directory.
• move: A map or multimap of source and destination paths to move.
  Similar to copy above, but removes the source.
• drop: A file or directory, or a list of files and directories, to
  remove from the module. Paths can contain * or ** globs.
• pick: A file or directory, or a list of files and directories, to
  include in the module. Everything else is dropped. Paths can contain
  * or ** globs.
• executable: A file or list of files to make executable, as if
  calling chmod +x. Also accepts globs.
• export: A subdirectory that peru should treat as the root of the
  module tree. Everything else is dropped, including parent directories.

Besides using those fields in your modules, you can also use them in "named
rules", which let you transform one module in multiple ways. For example, say
you want the asyncio subdir from the Tulip project, but you also want the
license file somewhere else. Rather than defining the same module twice, you
can use one module and two named rules, like this:

imports:
    tulip, asyncio: python/asyncio/
    tulip, license: licenses/

git module tulip:
    url: https://github.com/python/asyncio

rule asyncio:
    export: asyncio/

rule license:
    pick: COPYING

As in this example, named rules are declared a lot like modules and then
used in the imports list, with the syntax module, rule. The ,
operator there works kind of like a shell pipeline, so you can even do
twisted things like module, rule1, rule2, with each rule applying to the
output tree of the previous.

Recursion

If you import a module that has a peru file of its own, peru can include
that module's imports along with it, similar to how git submodules
behave with git clone --recursive. To enable this, add recursive: true in a module's definition.

It's also possible to directly import modules that are defined in the
peru.yaml file of another module. If your project defines a module
foo, and foo has a peru file in it that defines a module bar, you
can use foo.bar in your own imports. This works even if you never
actually import foo, and it does not require setting recursive: true.

Configuration

There are several flags and environment variables you can set, to
control where peru puts things. Flags always take precedence.

• --file=<file>: The path to your peru YAML file. By default peru
  looks for peru.yaml in the current directory or one of its parents.
  This setting tells peru to use a specific file. If set, --sync-dir
  must also be set.
• --sync-dir=<dir>: The path that all imports are interpreted
  relative to. That is, if you import a module to ./, the contents of
  that module go directly in the sync dir. By default this is the
  directory containing your peru.yaml file. If set, --file must also
  be set.
• --state-dir=<dir>: The directory where peru stashes all of its state
  metadata, and also the parent of the cache dir. By default this is
  .peru inside the sync dir. You should not share this directory
  between two projects, or peru sync will get confused.
• --cache-dir=<dir> or PERU_CACHE_DIR: The directory where peru
  keeps everything it's fetched. If you have many projects fetching the
  same dependencies, you can use a shared cache dir to speed things up.
• --file-basename=<name>: Change the default peru file name (normally
  peru.yaml). As usual, peru will search the current directory and its
  parents for a file of that name, and it will use that file's parent
  dir as the sync dir. Incompatible with --file.

Links

• Discussion and announcements (Google
  Group)
• Architecture doc
• Using peru with make