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Find the 20 biggest directories on the current filesystem
This command will tell you the 20 biggest directories starting from your working directory and skips directories on other filesystems. Useful for resolving disk space issues.

Bash prompt with user name, host, history number, current dir and just a touch of color
I put that line in my .bash_profile (OS X) and .bashrc (Linux). Here is a summary of what the \char means: n=new line, u=user name, h=host, !=history number, w=current work directory The \[\e[32m\] sequence set the text to bright green and \[\e[0m\] returns to normal color. For more information on what you can set in your bash prompt, google 'bash prompt'

remove recursively all txt files with number of lines less than 10

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.

Convert CSV to JSON
Replace 'csv_file.csv' with your filename.

Generate binary sequence data

Securely destroy data (including whole hard disks)
GNU shred is provided by the coreutils package on most Linux distribution (meaning, you probably have it installed already), and is capable of wiping a device to DoD standards. You can give shred any file to destroy, be it your shell history or a block device file (/dev/hdX, for IDE hard drive X, for example). Shred will overwrite the target 25 times by default, but 3 is enough to prevent most recovery, and 7 passes is enough for the US Department of Defense. Use the -n flag to specify the number of passes, and man shred for even more secure erasing fun. Note that shredding your shell history may not be terribly effective on devices with journaling filesystems, RAID copies or snapshot copies, but if you're wiping a single disk, none of that is a concern. Also, it takes quite a while :)

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"

Remove all but one specific file

move up through directories faster (set in your /etc/profile or .bash_profile)
You can also remove the "&& pwd" if you don't want it to print out each directory as it moves up.


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