Command History:

Any command executed on the machine gets logged. By default on bash the history size is 1000 commands. You can check your current size by

• $ echo $HISTSIZE

this setting is stored in .bashrc , if you open it up you ll see something like this

• HISTSIZE=1000 

It a good idea to increase the HISTSIZE to store a large number of commands, which can be rendered for quick execution with reverse-i-search.

There is also an interesting hack/trick around this :) . 

You can override the logging behavior but prefixing every command with a space. Interestingly commands executed in such fashion do not show up in the output of the 'history' command.

Also command history can be disabled by setting

• HISTFILESIZE=0

in .bashrc

Change default OS the hacker way

Well I had played with grub.cfg long time back but recently I had to install Ubuntu on my laptop which I rarely use ( as I believe kick ass developers don't work on laptop :P ) and especially with window$ on it.

So anyway , I installed Ubuntu but forgot to set the default OS to window$  , well you might be like

Yeah yeah , I tried persuading my family members to use Ubuntu but soon gave up on them :P.

A very shiny pearl of wisdom I have picked up is that , always create a backup of any config file you plan on tweaking.

So lets go ahead and make a original backup of the /boot/grub/grub.cfg file which will be changed to reset the default options.

• cd /boot/grub/
• sudo cp grub.cfg grub.cfg.org
• sudo vim grub.cfg
• search for set default with vim search i.e "/set default" this is generally line 13 in grub.cfg

• All the entries in the grub are associated with "menuentry" keyword in grub.cfg , for setting the default to windows OS we need to find the menuentry number for windows , these menuentry  starts with 0. If you are dual booted there are high chances that menuentry for windows would be 4.
  here in my case it has to be 4 , so I can change my default OS to window$ by pointing the default to 4.
• change the set default to the corresponding OS menuentry , for me it is 




• set default = "4"
• optionally while you are at it , you can even make the booting faster by changing the default time out to 2 sec or so.
• 

You can always use GUI grub config tools but 

Grep : recursively search for the occurrence of a word in files.

Lets assume we are trying to search word "this" in all the files in the present directory. Would it be nice if I could see which all files it occurs in along with the line number. Passing some options to grep commands helps to do the exact same task.

CLI: Quick command execution

There are very handy shortcuts available on the command line , lets just list em out.

• Execute last command
• $ !!
• well this feature is really useful when you want to execute last command again but with sudo privileges.
• $ sudo !!
• Go forward/backward command history with Ctrl+n and Ctrl+p.
• Access the last command argument with Alt + .
• Use reverse-i-search by pressing Ctrl+r to search the history in reverse order.

Vim: Sort the file contents

Lets say you have a file that looks like this

and all you want to do is get the content rearranged in sorted order. Well here is a quickie , enter visual mode by pressing v , press Shift+g to select entire file and then just execute the sort command.

and bang here is the sorted content.

Design Pattern : Command Pattern

Well this is the first time I have put efforts to see how my code look from design point of view using ObjectAid UML tool available for eclipse. Neat ! isn't it :P

Above figure shows a type of behavioral design pattern called Command Pattern in which an object is used to encapsulate the information needed to call a method of "Reciever" at a later time.

The sample code for is present on the github repo.

Bash : Start a process in background

$ Command &
e.g vihaan@trojan:~$ google-chrome &