Case study #2: packaging scons for Zero Install
This tutorial / case-study shows how scons (a make/autoconf replacement) can be made available through Zero Install. It is assumed that you have already read Case Study #1. We will not go over the same steps in detail here.
We begin by creating a directory structure on our local machine, as before:
$ mkdir scons.org $ mkdir scons.org/site $ mkdir scons.org/export
We fetch the release we want to make available and unpack it into a temporary directory. This is because, unlike Contacts in the previous study, scons needs an explicit install step, which copies files from the unpacked archive to their final locations on the system.
$ tar xzf scons-0.96.1.tar.gz $ ls scons.org scons-0.96.1
We will now tell scons to install to our site directory, using the --prefix option. We include the version number so that we can make multiple versions of scons available. We don't need a separate directory for each platform, because scons is pure Python code.
$ cd scons-0.96.1 $ python setup.py install --prefix=../scons.org/site/0.96.1 [...] Installed SCons script into ../scons.org/site/0.96.1/bin
Note that some software will include hard-coded paths to the site directory if you do this, but Python's distutils uses the prefix we give it only to decide where to put the files, not to affect the build itself. When packaging software which actually stores the prefix inside the created program, more care must be taken.
Now we create a symlink for the latest version. We also make a symlink for the main program to let people run the latest version easily:
$ cd ../scons.org/site $ ln -s 0.96.1 latest-1 $ ln -s latest-1/bin/scons scons-1
The -1 after latest means the latest version compatible with the scons v1 syntax. If, one day, a version of scons comes out which is not backwards compatible we can use a symlink named latest-2. Then software that needs scons v1 to build will still work in a Zero Install system (though not in traditional systems).
Now we run 0build to build the archives, as before:
$ alias 0build=/uri/0install/zero-install.sourceforge.net/bin/0build $ cd scons.org/site $ 0build ../export scons.org
After creating a new GPG key for the site (as before), 0build populates the export directory. Again, we create a 0push script to rsync the archives to the remote web server, and run that:
$ cd scons.org $ ./0push
Now it's time to test it (ideally from another machine). At this point it's a good idea to try renaming our site directory to make sure that scons isn't running anything from there (i.e., it is getting everything though Zero Install):
$ mv scons.org scons.org.renamed
$ cd /uri/0install/scons.org
$ ls
0.96.1 latest-1 scons-1
$ ./scons-1 -v
SCons by Steven Knight et al.:
script: v0.96.1.D001, 2004/08/23 09:55:29, by knight on casablanca
engine: v0.96.1.D001, 2004/08/23 09:55:29, by knight on casablanca
Copyright (c) 2001, 2002, 2003, 2004 The SCons Foundation
We're done! To make new releases, we:
- Run the setup program again with the new version number in the prefix.
- Run 0push to copy the new version across.
- Run 0refresh on our test machine and run bin/scons for the new version directly (not using the latest-1 symlink, which still runs the old version).
- Once we're confident that the new version works well, we update the symlink to point to it and run 0push again, making this the default version.
Using scons through Zero Install
People who want to use scons can 'install' it into their PATH in the usual way, eg:
# ln -s /uri/0install/scons.org/scons-1 /usr/local/bin/scons # scons
However, we can write our build scripts so that users don't have to do this. Eg, our project might have a build script containing:
#!/bin/sh if scons -v > /dev/null 2>&1; then scons elif [ -d /uri/0install/scons.org ]; then 0run "scons.org/scons-1 2004-11-10" else echo "You need scons (or Zero Install) to build this program." echo "You can get scons from http://www.scons.org" fi
This script will run a local version of scons if available. If not, it tests whether the user has Zero Install, and tries to run it though that if so.
