What is "Task" in the output of "apt-cache show package_name"?

Question

When I run apt-cache show inkscape, the bottom of the output has:

Description-md5: fed6589659211fb40b80d03dda6e5675  
Homepage: http://www.inkscape.org/  
Description-md5: fed6589659211fb40b80d03dda6e5675  
Bugs: https://bugs.launchpad.net/ubuntu/+filebug  
Origin: Ubuntu  
Supported: 9m  
Task: ubuntu-usb, edubuntu-desktop-gnome, edubuntu-usb, ubuntustudio-video, ubuntustudio-graphics  

But when I run apt-cache show pdfgrep, the line beginning with Task is absent:

Description-md5: 8c8a5397f782d81d957740280eb8f352
Homepage: http://pdfgrep.sourceforge.net/
Description-md5: 8c8a5397f782d81d957740280eb8f352
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Origin: Ubuntu

Why is the line beginning with Task present for some packages and not for others?

Answer 1

The Task field in your output means that the package is part of the task edubuntu-desktop-gnome for example.

This function is similar to that of meta-packages, and, in fact, most (but not all) of the tasks available from tasksel (task select) are also available as meta-packages.

To install tasksel type:

apt-get install tasksel

You can list all available tasks with this command (output stripped), but tasksel must be installed first:

root@host:~# grep 'Task\|Description' /usr/share/tasksel/ubuntu-tasks.desc
...
Task: minimal
Description: Minimal base system
...

You can also invoke tasksel as root by:

root@host:~# tasksel

You may know this from the installation routine, because those "tasks" are normally installed during early system setup.

So, those packages in apt-cache show that have not the Task field (pdfgrep in your question) are not part of a task and will not be installed when you install a task via it's meta-package or tasksel. On the contrary inkscape is part of many different tasks, whose meaning you can find in /usr/share/tasksel/ubuntu-tasks.desc.