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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"

Continuously listen on a port and respond with a fixed message with netcat (and respond to kill signals)
`while true`: do forever `nc -l -p 4300 -c 'echo hello'`: this is the but anything can go here really `test $? -gt 0 && break`: this checks the return code for ctrl^c or the like and quite the loop, otherwise in order to kill the loop you'd have to get the parent process id and kill it.

Random quote from Borat
I improved a bit on the original by only using sed and extracting the quote with a matching group. Use -nE for sed on Mac OSX Use -nr for sed on Linux. Warning! The quotes from Borat are definitely offensive.

Set laptop display brightness
Run as root. Path may vary depending on laptop model and video card (this was tested on an Acer laptop with ATI HD3200 video). $ cat /proc/acpi/video/VGA/LCD/brightness to discover the possible values for your display.

Set OS X X11 to use installed Mathematica fonts

easily strace all your apache processes
Will open strace on all apache process, on systems using sbin/apache (debian) or sbin/httpd (redhat), and will follow threads newly created.

How to backup hard disk timely?
'data' is the directory to backup, 'backup' is directory to store snapshots. Backup files on a regular basis using hard links. Very efficient, quick. Backup data is directly available. Same as explained here : http://blog.interlinked.org/tutorials/rsync_time_machine.html in one line. Using du to check the size of your backups, the first backup counts for all the space, and other backups only files that have changed.

One command line web server on port 80 using nc (netcat)
Very simple web server listening on port 80 will serve index.html file or whatever file you like pointing your browser at http://your-IP-address/index.html for example. If your web server is down for maintenance and you'd like to inform your visitors about it, quickly and easily, you just have to put into the index.html file the right HTML code and you are done! Of course you need to be root to run the command using port 80.

Install pip with Proxy
Installs pip packages defining a proxy

Remove everything except that file
Remove everything except that file with shell tricks inside a subshell to avoid changes in the environment. $ help shopt


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