scan an image:
scanimage -d pixma:04A91901 --resolution 75 -l 75 -t 32 -x 25 -y 230 >scan

convert an image:
convert -crop 50x50+10+10 scan scan.jpg

mount a truecrypt volume:
truecrypt -k "" --protect-hidden="no" /true/crypt/file.tc /mountpoint

make/update a backup:
rsync -a --stats /from /to

transcode a video:
mencoder fromfile.avi -ovc lavc -oac copy -of lavf -lavcopts vcodec=mpeg4:vbitrate=800:acodec=libmp3lame:abitrate=128 -o tofile.mp4
ffmpeg -i fromfile.avi -vcodec mpeg4 -vb 907000 -acodec libmp3lame -ab 128000 tofile.mp4

burn an audio cd:
icedax -D/dev/cdrw -B
wodim *.wav


youtube-dl url -F
youtube-dl url -f id

download xkcd:
for i in {1..1197}; do wget -nH -A jpg,gif,png -R a899e84.jpg,terrible_small_logo.png -p -H -D xkcd.com  http://xkcd.com/$i/ -P $i; done
perl -e 'for $f (glob("*/comics/*")){ $f=~/(\d+)\/comics\/(\S+)/; system sprintf "mv \"$f\" \"%04s-%s\"\n", $1,$2; }'

download some tits:
wget -r -A jpg,gif,png -H -D kiinnostaa.org kiinnostaa.org


regex substitute on files, keeping modification times:

from="from"
to="to"
files=*
for a in `grep -l $from $files`; do
    mtime=`stat -c%Y $a`
    sed -e "s/$from/$to/" -i $a
    touch -d @$mtime $a
done


remove duplicate lines:
| sort | uniq -c | sort -n