Merging PDF files (and more!)

My mobile phone company decided, 7 months ago, to save the world by not sending paper invoices any more. Unfortunately they didn't tell me (and registering to see invoices online required jumping through lots of hoops, while holding a PIN number I didn't know).
All sorted now, and I only lost one invoice (they only keep the last six online). So I downloaded six shiny new PDF files. Like my phone company I also want to save the world, so wanted to print them four to a page.

The solution is pdftk (in Ubuntu's package list; also available for other major distributions I believe). This simple command:
pdftk 2008*.pdf cat output all.pdf

It just worked. Nice. It also does lots of other cool stuff, like adding or removing encryption, remove just one page out of the middle of a PDF, rotate, extract text. No mention of i18n, so I don't know (yet) how it will cope with Japanese PDFs. Or PDFs where the text is actually an image. The projects home page is http://www.accesspdf.com/pdftk/

It appears there are also Windows and Mac versions.

Gnome file extensions are screwing up my life!

Okay, perhaps a touch of frustration crept into that choice of subject.
When you double click a file in gnome file manager a lot of the time it works. When it doesn't you are in deep trouble. I've visited this problem before:
http://darrendev.blogspot.com/2008/06/gnome-file-associations-air-and-zip.html
http://darrendev.blogspot.com/2008/05/gnome-whether-under-redhat-or-ubuntu-is.html

I never did fix the AIR problem - I had to uninstall AIR completely.
Now, since yesterday, all my inc files refuse to open in SciTE. They say "this claims to be an inc file, but the contents look like PHP. Even though SciTE is your editor of choice for both inc and php files I'm not going to let you open it. Please also check behind the sofa for terrorists."

I suspect it was because I was editing an inc file in jedit a few days ago and manually chose PHP for the syntax highlighting. But if so, how and why is jedit allowed to alter my system configuration??
(I've also noticed that when clicking links within zip files gedit is now associated with txt files; it used to be open office writer. Something weird is going on, but at least this one is an improvement: application associations in zip files are a world of their own, and I've never tracked down any method of configuring them.)

Following my advice in the second of my above blog entries I tried making a php.xml file for *.inc files. But no luck there.

Somebody help! How do I restore this? Or, even better, how do I switch off Gnome's stupid wrong-extension-is-a-security-risk check? In many years of using gnome it has never once complained in a useful way, or detected a genuine problem. Every single time it has just got in the way.

(If you type "gnome-control-center" there is supposed to be an icon in there for file types. It is missing in ubuntu 7! Or perhaps it was only in there in gnome 1 and got removed in gnome 2.)

UPDATE: Problem half-solved. I've installed PC File Manager, and replaced Nautilus everywhere. See the instructions here:
http://linuxondesktop.blogspot.com/2008/05/replacing-nautilus-with-quicker-and.html
(they say Ubuntu 8 but everything seems to apply to Ubuntu 7 fine.)
I had to go through each text file extension and assign it to /usr/bin/scite (it was defaulting to jedit for most of them, and defaulting to nothing for the troublesome *.inc), but after I did that it is working nicely. File associations appear to be much more transparent than in Nautilus.
However following instructions in 2nd post here: http://ubuntuforums.org/showthread.php?t=692238 for replacing the desktop didn't go so well. The icons cannot be moved around on the desktop, and launchers were not working. So I undid those changes, and will now try and change my directory launchers on my desktop to use pcmanfm. It seems I'll need to go through and replace each "location launcher" with an application launcher that calls pcmanfm. A bit of a pain, but looks like it will work.

Perhaps I'll investigate kubuntu... Surely KDE cannot be worse than Gnome/Nautilus?

linux shell: two directories quick switch

Sometimes I have to work in two directories from the commandline. For instance to check a log file got created, then back to the directory where the command I am testing is run from. The quick tip is simply "cd -". This takes you back to the previous directory. If you type it again it takes you back to where you were, acting as a nice toggle.

"cd" with no parameters takes you to your home directory. "cd ~/somewhere" takes you directly to a directory relative to your home directory (i.e. tilde expands to your home directory). I had a hunt around but couldn't find any other special characters to use with "cd", but if you know one please let me know.

(This tip was found in Linux Magazine, June 2008)