That’s it using a regular expression we can check if a number is prime or not.

Here is a short explanation of why it works (though it will ruin the magic part):

The trick is first to “flatten” the number. i.e., for 7, we’ll pass (“1″ * 7) to the regexp, that is: “1111111″.
The first part of the regexp “^1?$” matches a string with an optional “1″, that is, it matches the empty string, and the string “1″, which are the “flat” representations of 0 and 1 respectively.

The second part is more tricky:
It tries to match a string of “start of line”, then two 1′s or more ^(11+?), then it tries to find one or more times the previous match (\1+). then end of line $.
If you imaging “sticks” instead of the 1′s, then what we did is: represent 7 (for example) with 7 sticks, then try to divide them into two or more groups of two, or two or more groups of three, etc.. in general: try to divide the sticks into two or more groups of “two or more”. Which is exactly the definition of a non-prime number (a.k.a composite number).
So, if the regexp succeeds to match the pattern, the number is not prime. If it fails, the number is prime.

So easy, so elegant

Note about the ^(11+?): This is almost the same as ^(11+) but, with one difference: using (+?) instead of (+) means “match minimally”, as opposed to “match greedily”.
For example, consider the string “aaaa” and the regexp ‘(a+)\1+’ the regexp will match the string, the value of \1 will be “aa”, since the a+ pattern matched the longest string which allows the regexp to match the string.
The regexp ‘(a+?)\1+’ will also match the string, but the value of \1 will be “a”, because this time (a+?) looked for the minimal match which will allow the regexp to match the string.
In out case, the use of (+?) instead of (+) does not affect correctness (that is, we could use (+) and the regexp will still work correctly). The only difference is related to performance, because our case tries small groups first, while the other case tries big groups first.

More information and explanation in the original article.

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Regular Expression To Check For Prime Numbers

If you use Firefox, then you can easily solve this problem with these two Firefox extensions. Both serve the same purpose: Making websites easier to read, by removing distractions and allowing you to focus on the content instead. Each one displays the website in a different style, and they have different options. I installed both and use them alternately (and regularly).

The first extension is called “Readability”, and is found here. The other is called “Firefox Reader”, and is located here.

Using is as easy as clicking a button, so I’m sure you’ll be able to manage without my help

Here are some screenshots of Dr Chip’s Website without and with the above extensions:

Dr Chip's Website - Original

Dr Chip's Website With Readability Extension

Dr Chip's Website With Firefox Reader Extension

Have fun

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Firefox Extensions To Make Web Pages More Eye Friendly

Using colormake, colorgcc and colordiff, you can have the output of make, gcc, diff (respectively) coloured.

To install in Ubuntu:

sudo apt-get install colorgcc colormake colordiff

You might want to use aliases to override the normal make/gcc/diff commands.

Original tip from here.

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Colorize Make, GCC and Diff’s Output

You’re editing a buffer in vim, you copy a text (say, code snippet) from another place (say, Firefox), and you paste it inside vim (with middle mouse button / shift+insert). Most chances you won’t like what vim has just did to your text.

The problem is that vim doesn’t “know” that you’re actually pasting a text, and it thinks that you’re typing. So, if you have indentation enabled, it will re-indent your text.

The solution is simple: Whenever you want to paste text from outside vim into vim. Type this in command mode:

:set paste

So now vim knows that you’re going to paste text, and it will not touch it.

To disable the paste mode:

:set nopaste

As easy as that

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Fix Bad Indentation When Pasting Text To Vim

Recently, I started to use tmux, and opened vim, split the windows as usual, and tried to resize them. It didn’t work

I use Ubuntu 10.04 (Don’t remember the exotic name..), and I found that the latest tmux package in their repo is 1.1-1.

Anyway, version 1.1-1 has a bug with the NumPad. The solution is to download the source of tmux 1.2 and build it. It depends on libevent so you’ll need to get it first:

this is how to make it work:

1. sudo apt-get install libevent-dev

2. Get the source tarball of tmux from here.

3. tar xzf tmux-1.2.tar.gz

4. cd tmux-1.2

5. ./configure

6. make

7. sudo make install

Done. Now your life is better. Have fun

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NumPad Problems When Using Vim over Tmux

I happened to write JavaScript this week, and found a great Online JavaScript Lint.  Use with care

Ah, and they also have a downloadable version.

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Online JavaScript Lint

If you use Facebook, the first thing you should know is: Never trust these bastards! They don’t give a shit on your privacy, they want (and do) own YOUR data, they can “deactivate” your account without a warning, without an explanation, and even without a good reason.

A friend of mine got a letter from Facebook today, informing him that for some reason his Facebook account ws deactivated (I assure you that none of there “reasons” is reasonable). Not only that, they end the message with

“Your violation of Facebook’s standards has resulted in the permanent loss of your account. We will not be able to reactivate your account for any reason. This decision is final.”

WTF?! Final? What could made such decision final? What if he has an explanation? What about the man’s data, photos, posts, contacts?!

Know what? I have a theory.  “Violation of Facebook’s standards” isn’t a good reason to make a decision final. My theory is: The bastards accidentally lost his data, and now they try to cover their a**es using the “Violation of standards”.

You thought that you are using Facebook? You’re wrong, Facebook is using you! Not only using you, they actually OWN YOU!

I learnt a few lessons from this accident:

1. Never trust a corporation when it comes to your data or privacy. If they want, they can erase everything at once, without a warning, or a reason.

2. Never trust Facebook. These are real bastards. Worst than any other corporation. Your data is their money. Ethics is not their strong side.

3. Never use Facebook (or any social network) for storage. Don’t upload content explicitly to Facebook, reliability isn’t their strong side neither. In the worst case, save your data in other websites as well (like Picasa/Flickr for Photos etc..), of course, a local copy in your machine isn’t a bad idea.

4. Backup! Don’t let yourself lose your data without being able to do anything.

There is a great tool to backup your Facebook data, it’s called “Social Safe“, it’s not free but it’s very cheap (3 USD). Really recommended. If you use it on Linux, you can find the backed-up data on:

/home/[username]/.appdata/com.1minus1.socialsafe.*/Local Store/facebook/

5. If you don’t want Facebook to own your own data (Damn it!), don’t upload it to them.

Have a good day

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Backup Your Facebook Data

Here’s how to do it:

Step 1: Unpack (from O’Reilly’s website)

1. Once you’ve downloaded the app, select Applications in iTunes, right-click the app that you want to extract, and select Show in Finder/Explorer. The file you want is selected automatically when the window opens.
2. Copy (that’s copy, not move) the file to a different location, for example, your desktop.
3. Change the file extension of the copied file from .ipa to .zip using whatever method is most familiar to you.
4. Unzip the file using whatever archiving utility you prefer.
5. There are a few files, but the directory you are interested in should be named Payload.
6. This step varies, depending on platform:
* If you are on a PC, simply go into the Payload/.app directory.
* If you are on a Mac, go into the Payload directory, right-click the file within, and select Show Package Contents.
7. Again, there are lots of files and directories here, but the EPUB content is found in book/OEBPS.

Now that you’ve found the files, you are free to read (and copy and paste from) them in your web browser.

Now that you have the whole book as HTML, you can read it through a web browser. You can also pack it as a epub file:

Step 2: Repack
Go to “Payload/.app/book/” inside the unpacked app directory.
Now, run these commands (Work in Linux. Maybe there is some analogous commands for other OSes):

zip -q0X my_book.epub mimetype
zip -qXr9D my_book.epub *

credits: bobdc.blog

Step 3: Upload to Stanza
There are a few methods. All of them are over WiFi (i.e. you need to have you iPhone connected to the same Wireless network as your compute). They are listed here

Of course, if you have many books, you might save time by recruiting a script to do most of the work instead of doing it manually

Credits for collecting the pieces together: Sanders Kleinfeld at getsatisfication.

Have fun

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Convert O’reilly Stand-Alone iPhone Books to epub Format

:TOhtml

A new buffer will be opened with the HTML source, just save it:

:wq

If the original file name was “mycode.c”, you’ll find a new file in the same directory named “mycode.c.html”. Open it with your favourite web browser.

Wow, not?
Have fun

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Vim Tip – Convert Code To HTML

That’s it, the trick is to use the curly brackets ${var} to separate the variable from its surrounding.

Have fun

source: @bashcookbook

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Bash Tip – Separate a Bash Variable From Surrounding Letters