Ubuntu / Linux news and application reviews.

1. Show installed but unused linux headers, image, or modules:
dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ ]*\).*/\1/;/[0-9]/!d'

If you would also like to purge them too:
dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ ]*\).*/\1/;/[0-9]/!d' | xargs sudo apt-get -y purge

2. Rip audio from a video file:
mplayer -ao pcm -vo null -vc dummy -dumpaudio -dumpfile <output-file> <input-file>

You can also extract the sound from a flv and make an mp3 with:
ffmpeg -i input.flv -f mp3 -vn -acodec copy ouput.mp3

3. Stream YouTube URL directly to mplayer:
mplayer -fs $(echo "http://youtube.com/get_video.php?$(curl -s $youtube_url | sed -n "/watch_fullscreen/s;.*\(video_id.\+\)&title.*;\1;p")")

(Replace $youtube_url with any youtube URL)

4. Download all images from a site:
wget -r -l1 --no-parent -nH -nd -P/tmp -A".gif,.jpg" http://example.com/images

5. Create a nifty overview of the hardware in your computer:
lshw -html > hardware.html

(then open hardware.html in a web browser).

6. Cut a part of a video:
ffmpeg -vcodec copy -acodec copy -i orginalfile -ss 00:01:30 -t 0:0:20 newfile

Where 00:01:30 is the start time (replace with your own) and 0:0:20 is the length of the video you want to cut out (replace with the length you desire).

7. Purge configuration files of removed packages on debian based systems:
sudo aptitude purge `dpkg --get-selections | grep deinstall | awk '{print $1}'`

8. Play high-res video files on a slow processor:
mplayer -framedrop -vfm ffmpeg -lavdopts lowres=1:fast:skiploopfilter=all

9. Convert images to a multi-page pdf:
convert -adjoin -page A4 *.jpeg multipage.pdf

10. Find the 20 biggest directories on the current filesystem:
du -xk | sort -n | tail -20