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get the full description of a randomly selected package from the list of installed packages on a debian system
I put this command on my ~/.bashrc in order to learn something new about installed packages on my Debian/Ubuntu system each time I open a new terminal

Pass TAB as field separator to sort, join, cut, etc.
Use this BASH trick to create a variable containing the TAB character and pass it as the argument to sort, join, cut and other commands which don't understand the \t notation. $ sort -t $'\t' ... $ join -t $'\t' ... $ cut -d $'\t' ...

get a fresh commandlinefu-item each day as motd
Commandline-fu often has little tricks that I always forget. By adding this to the root-cron (sudo crontab -e) I lean a new trick every day.

Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)
Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

Verify/edit bash history command before executing it
Bash history commands are those that begin with the character ! (eg. the most popular 'sudo !!' Explained here => http://www.commandlinefu.com/commands/view/13). By default bash immediately executes the history command. Setting this shell option will make bash first allow you to verify/edit an history command before executing it. To set this option permanently, put this command in ~/.profile or ~/.bashrc file. To unset this option issue following command. $shopt -u histverify

Check if you work on a virtual/physical machine in Linux
Command used to know if we are working on a virtual or physical machine. This command will use the dmidecode utility to retrieve hardware information of your computer via the BIOS. Run this command as root or with sudo.

check open ports without netstat or lsof

sort monthwise
sort command can sort month-wise (first three letters of each month). See the sample output for clarification. Sorting Stable ? NO. Take note if that matters to you. Sample output suggests that sort performs unstable sorting (see the relative order of two 'feb' entries).

List users with running processes
This is different that `who` in that who only cares about logged-in users running shells, this command will show all daemon users and what not; also users logged in remotely via SSH but are running SFTP/SCP only and not a shell.

Command line calculator
This opens a python command line. You can use math and random and float-division is enabled (without appending .0 to integers). I just don't know how to specify a standard precision.


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