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Use Perl like grep
If you've ever tried "grep -P" you know how terrible it is. Even the man page describes it as "highly experimental". This function will let you 'grep' pipes and files using Perl syntax for regular expressions. The first argument is the pattern, e.g. '/foo/'. The second argument is a filename (optional).

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Combines an arbitrary number of transparent png files into one file
This one liner; combines all sequentially numbered files; in this example IMG_0001.png to IMG_1121.png by generating the shell script, making the shell script executable and then running the shell script to combine the 1121 png into a single png file named _final.png tested on Mac OS X 10.6.3 with ImageMagick 6.5.8-0 2009-11-22 Q16 http://www.imagemagick.org

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

extract email addresses from some file (or any other pattern)

Resume scp of a big file
It can resume a failed secure copy ( usefull when you transfer big files like db dumps through vpn ) using rsync. It requires rsync installed in both hosts. rsync --partial --progress --rsh=ssh $file_source $user@$host:$destination_file local -> remote or rsync --partial --progress --rsh=ssh $user@$host:$remote_file $destination_file remote -> local

Indicates the position of my monitor buttons
I often need to change the brightness of my monitor. The symbols of the sensor buttons are not illuminated and on a black background .... invisible! Now i use osd_cat instead of a torch ;-)

Record a screencast and convert it to an mpeg
Grab X11 input and create an MPEG at 25 fps with the resolution 800x600

Ping all hosts on 192.168.1.0/24


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