bpt 0.2a

Tool to create isolated environments

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What is BPT

BPT is a Python library (bpt) and a command line application (box) to create and manage isolated enviroments, or boxes. Boxes are relocatable, which means that they can be moved to a different directory or even distributed to other machines (provided that the architecture is compatible). Packages inside the box can be easily disabled, enabled and removed, so that different versions of the same software can be installed simultaneously, allowing to switch between them.

BPT is similar in some ways to virtualenv, but it is not restricted to Python packages, allowing to install virtually any Unix software. It also takes some ideas from jhbuild, but without the dependency resolution and automatic downloading machinery, and the bpt-rules format is inspired by Gentoo’s ebuilds.

How to use it

A box is a directory whose structure resembles /usr/, that can contain one or more software packages. Each package is contained in a subdirectory of the pkgs directory in the box. A box contains a script, env, which sets up the environment, putting all the libraries, executables, etc. in the path.

The command to create a box is:

$ bpt/box create my_first_box

(We assume that the source distribution of BPT is in the directory bpt)

This creates the basic structure:

$ find my_first_box
my_first_box
my_first_box/bin
my_first_box/bpt_meta
my_first_box/bpt_meta/box_info
my_first_box/env
my_first_box/include
my_first_box/lib
my_first_box/man
my_first_box/pkgs
my_first_box/share

To execute a command within the box environment, use the env script:

$ my_first_box/env 'echo $PATH'
/tmp/box_87a482cc-34fc-11de-865a-001ec21bf2c7/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/local/bin

Even if it may not seem obvious at first, the first path points to the box’s bin. We’ll talk about this later in the How it works section. Prefixing env to every command can be annoying, so box has a shell command that spawns a shell with the environment set up. The env script exports also an environment variable, BPT_BOX_PATH, that box uses to know the location of the current box:

$ bpt/box -b my_first_box/ shell
(my_first_box) ot@brian ~ $ echo $BPT_BOX_PATH
/Users/ot/my_first_box

To install packages into a box, box offers two different commands: build and autobuild. The first works with sourcedirs: a sourcedir is a directory that contains a bpt-rules file, which contains the instructions to build the software. A good practice is to install BPT itself into the box (the source distribution of BPT is a sourcedir):

(my_first_box) ot@brian ~ $ bpt/box build bpt
INFO:BPT:Using current box "my_first_box"
INFO:BPT:Building application bpt, in sourcedir work/experimental/bpt
...
(my_first_box) ot@brian ~ $ which box
/tmp/box_87a482cc-34fc-11de-865a-001ec21bf2c7/bin/box

Now we can run the shell using the box’s box:

$ my_first_box/env box shell
INFO:BPT:Using current box "my_first_box"

(my_first_box) ot@brian ~ $

Another example of sourcedir is given by python30 in the examples directory, which installs python 3.0.1:

(my_first_box) ot@brian ~ $ box build examples/python30/
...

(my_first_box) ot@brian ~ $ python3.0 --version
Python 3.0.1

The autobuild command instead tries to build and install a tarball. It works when the software builds using the usual configure/make or setup.py:

(my_first_box) ot@brian ~ $ box autobuild Downloads/ipython-0.9.1.tar.gz
INFO:BPT:Using current box "my_first_box"
INFO:BPT:Guessed application name "ipython", version "0.9.1". Unpacking the file...
INFO:BPT:Building and installing as package ipython-0.9.1
...

(my_first_box) ot@brian ~ $ which ipython
/tmp/box_87a482cc-34fc-11de-865a-001ec21bf2c7/bin/ipython

(my_first_box) ot@brian ~ $ box autobuild Downloads/sqlite-amalgamation-3.6.3.tar.gz
INFO:BPT:Using current box "my_first_box"
INFO:BPT:Guessed application name "sqlite-amalgamation", version "3.6.3". Unpacking the file...
INFO:BPT:Building and installing as package sqlite-amalgamation-3.6.3
...

(my_first_box) ot@brian ~ $ which sqlite3
/tmp/box_87a482cc-34fc-11de-865a-001ec21bf2c7/bin/sqlite3

The status command shows the installed packages:

(my_first_box) ot@brian ~ $ box status
INFO:BPT:Using current box "my_first_box"

PACKAGE                       | NAME                | VERSION   | STATUS    |

bpt-0.1                       | bpt                 | 0.1       | enabled   |
ipython-0.8.4                 | ipython             | 0.8.4     | disabled  |
ipython-0.9.1                 | ipython             | 0.9.1     | enabled   |
python30-3.0.1                | python30            | 3.0.1     | enabled   |
sqlite-amalgamation-3.6.3     | sqlite-amalgamation | 3.6.3     | enabled   |

Packages can be enabled/disabled with the enable/disable commands:

(my_first_box) ot@brian ~ $ box disable python30-3.0.1

(my_first_box) ot@brian ~ $ python3.0
bash: python3.0: command not found

(my_first_box) ot@brian ~ $ box enable python30-3.0.1

(my_first_box) ot@brian ~ $ python3.0 --version
Python 3.0.1

Executing disable with the --remove switch deletes permanently the package files.

Features

TODO

Use cases

TODO

How it works

TODO

Writing the bpt-rules file

TODO

Supported operating systems

BPT should work with any POSIX operating system. It has been tested on Mac OS X Leopard and several Ubuntu releases.

License

BPT is distributed under the terms of the GPL License. The full license is in the file COPYING, distributed as part of this software.

Credits

• Giuseppe Ottaviano <giuott at gmail dot com>