[cydia-packagers] new dpkg control script: extrainst_

[Jay Freeman (saurik)]

I get a lot of requests for things like "I want to run stuff after the install, but only on install, not on upgrade". APT/dpkg is miserable at this. Its sad, but true. It has a file called postinst, but postinst is really designed for reconfiguring a package, not for installing it: its called /long after/ the package is installed (like, APT will go on and install more things and then queue up the postinst files to the very end) and it doesn't /really/ know anything about the package.

Example: in a postinst you know that the previous configuration on disk was from version 1.0, but not that 1.0 itself was actually on disk. And if you are a new install it still tells you that /you're/ already the configuration there (which is really just a stupid semantic).

/So/, after dealing with an issue in a package with _BigBoss_, I have decided to do something about this: I have added to dpkg a new script called extrainst_. This script takes one of two arguments: install or upgrade (in which case you also get the version you are upgrading from), and is designed to completely ignore configuration files (so if you were previously in a configuration file only state that isn't considered "installed"). I believe that this new script now provides a very simple conceptualization for how you do "extra stuff" during an install.

In fact, if you are previously coming from Installer, this script will likely feel like "ahhhh".

To use this new script (which yes, really ends in an underscore) your package should Pre-Depends: dpkg (>= 1.13.25-5). This will make it so that that version of dpkg is actually available during the install and is used to run the scripts. (Yes, this will work even during the install using the old version of dpkg to upgrade dpkg and then switching to the new version of dpkg to install your script ;P).

If this script fails then the install is considered to not have worked and the installation procedure will get rolled back (files will get removed, replaced back to the backup copies if it was an upgrade, and a million random scripts will get called with irritatingly complicated to remember arguments).

(Note that this version of dpkg isn't up right now, but will be up within an hour or two: i.e., long before any of you is likely to bother to try to use it ;P).

An example extrainst_:

#!/bin/bash

if [[ $1 == install || $1 == upgrade ]]; then
    do_something awesome
fi

if [[ $1 == upgrade && $2 == 1.0-4 ]]; then
   fix_bug_in old version
fi

-J
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