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Write comments to your history.
A null operation with the name 'comment', allowing comments to be written to HISTFILE. Prepending '#' to a command will *not* write the command to the history file, although it will be available for the current session, thus '#' is not useful for keeping track of comments past the current session.

drop first column of output by piping to this
An advantage is that this doesn't modify remained string at all. One can change {0,1} with {0,n} to drop several columns

Create full backups of individual folders using find and tar-gzip
Problem: I wanted to backup user data individually. In this example, all user data is located in "/mnt/storage/profiles", and about 25 folders inside, each with a username ( /mnt/storage/profiles/mike; /mnt/storage/profiles/lucy ...) I need each individual folder backed up, not the whole "/mnt/storage/profiles". So, using find while excluding directories depth and creating two variables (tarfile=username & desdir=destination), tar will create a .tgz file for each folder, resulting in a "mike_full.tgz" and "lucy_full.tgz".

get a desktop notification from the terminal
tired of switching to the console to check if some command has finished yet? if notify-send does not work on your box try this one... e.g. rsync -av -e /usr/bin/lsh $HOME slowconnection.bar:/mnt/backup ; z (now fire up X, do something useful, get notified if this stuff has finished).

Use CreationDate metadata on .mov files to rename and modify the created/modify file dates on Mac

Beep siren
Infinitely plays beeps with sinusoidally changing sound frequency. Ideal for alarm on an event.

Drop or block attackers IP with null routes
Someone might attack on your system. You can drop attacker IP using IPtables. However, you can use route command to null route unwanted traffic. A null route (also called as blackhole route) is a network route or kernel routing table entry that goes nowhere. Matching packets are dropped (ignored) rather than forwarded, acting as a kind of very limited firewall. The act of using null routes is often called blackhole filtering.

Run the last command as root
this command also can run the last command as root what's more, sudo !-2 can run the second last command as root , and so on

convert single digit to double digits
each number in a file name gets expanded to the number of digets provided as arg_1 of the arguments in rjust_file_nums. Put the funciton in the .bashrc file. Be sure to $ source ~/.bashrc so that the function will be accessible from bash.

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


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