CommandNotFoundMagic

Revision 8 as of 2006-06-25 02:50:39

Clear message

Summary

The "command not found" message is not very helpful. If e.g. the unzip command is not found but it's available in a package, it would be very interesting if the system could tell that the command is currently not available, but installing a package would provide it.

Rational

Because ubuntu ships only with a single CD some commands that power-users expect are not installed (e.g. gcc, make).

Use cases

  • John sees a tutorial of how to unzip a package using the unzip command, and tries to follow it. The needed package is not installed, so he gets a message saying that installing the mentioned package is needed.

Design

Bash has a "command_not_found" handler that is called in the interactive mode when a command is not found. The first argument is the command that is not found. We hook a custom python script into it that has a database (gdbm or similar) with the available commands as keys and some information (like a list of packages it is in) as value. This lookup needs to be fast. This information is assembled from various sources:

  • from the Content-$arch file
  • from a "by-hand" file to include additonal stuff (like acroread)

  • a mirror with deb that are scanned for update-alternatives commands in

    • postinst

Implementation

Code is available in http://ubuntu.suxx.pl/2006--1/bzr-archive/command-not-found--main/ and http://people.ubuntu.com/~mvo/bzr/cmd-not-found--mvo/

Problems

The real evil for this spec is the "update-alternatives" command. A common applicatoin like "vi" is not shiped by the various packages as "vi" but as "vim","nvi", etc and updated via update-alternatives to "vi" in the postinst scripts. This needs to be evaluated as well. The problem is that some packages embed the call in bash code with "update-alternateive $pkg" (e.g. the emacs postinst), making it hard to automatically parse the code.

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