Brilliant 8-phase multi-quine in ruby

Wikipedia defines quine as:

A quine is a computer program which takes no input and produces a copy of its own source code as its only output.

In layman terms, it is a program that when executed outputs itself. Like a C program outputting its own source code. Kleene's Recursion Theorem proves the existence of quines in any Turing Complete Language. Its a good exercise to write one in your favorite language. Its fascinating to see quines.

Today morning my friend Umesh showed me this brilliant piece of ruby code that behaves as a Multi-quine. Link to original post by its author. Here's a listing of the same:



Save it as "test.rb" and run the following shell script:

while true;
do
    clear
    ruby test.rb | tee test2.rb
    mv test2.rb test.rb
    sleep 1
done

You will be able to see the picture changing after every 1 second and returning back to the original after 8 seconds. Note that when you run test.rb, it produces the output which is used for the next iteration. The shell script code lines 4 and 5 runs the code and uses the output of the code to replace the original code.

After being amazed by the beauty of this piece of code, I am not trying to figure out how exactly does it achieve this result. Someday I will post the same code with indentations and explanations in this blog.

Make Your Own Command-line Calculator with bc

I do not know about you, but I am bothered by the lack of a proper command line calculator for doing small single line calculations in Linux (or any other UNIX or Mac system). Sure bc is there but it does not support floating point by default, so one ends up writing things like:

echo "scale=3; 22/7" | bc

which is quite cumbersome for day to day work.

To subvert this trouble, I wrote the following two-liner and saved it as "calc" in a directory in PATH:

#! /bin/bash
echo "scale=3; $1" | bc; exit

Then do a "chmod +x" on the file to give it execute permission. This does the same thing as the above script, but is way simpler to use:

calc 22/7

The command "scale=3" was to instruct bc to print upto 3 decimal digits. You can change it as per your requirements.

The bc utility can do way more than this simple calculations. For example it can handle different bases and load functions from files. To know more about its capabilities try the good old "man bc" in terminal or read an online reference like this one on about.com.  You can read more about its advanced capabilities from an old but quite relevant article in LinuxJournal "bc: a handy utility".

Disclaimer : Although the script was by me, the idea is not new. In fact a lot of my colleagues use similar scripts for their own daily work.

Do-while loop in Ruby

As you know, I'm trying out Ruby. While solving one of the exercise problems I felt the need for a do-while loop. Unfortunately ruby has no documented do-while loop. Thankfully, somebody has already asked this same question in stackoverflow : Is there a do-while loop in ruby?

Here is a demonstration of a do-while code in ruby:


Remember that using undocumented features is always ill-advised !!

I'm trying out Ruby

I have always been interested in programming languages. After coding in a plethora of mainstream procedural languages C, C++ and Java, last year I tried my hands on Python. Apart from being an enjoyable experience, learning Python has paid off quite well while building prototypes in my work. This prompted me to try learning some other languages.

While searching for a cool language to try out, I came across the book, "Seven Languages in Seven Weeks" which promises to go beyond the simple tutorials and "introduction to" and introduce some non-trivial aspects of the language. I have started from page 1 and am exploring Ruby. So far the author has kept up his promise.

Ruby has got very friendly constructs and syntactic sugars like:

• the keyword "until", which is simply a negation of the popular "while"
• instead of simple "for" loops, constructs like "10.times"

which gives a warm and friendly feeling to the language. Besides the book mentioned above I am using "Programming Ruby 1.9" from the same publishers for a reference.

Demystifying bulk SMS sender name

With the high penetration of mobile phones, companies have started sending out automated sms. I have always wondered about the cryptic sender names. Careful observations about the sender name reveals:

• all letters are in capitals
• name format is **-******
• the first two letters seem random
• followed by an hyphen
• followed by a six letter
• last six letters seem to identify the sender name
• for example presently, "SBIINB" represents SBI bank
• sometimes the same sender can send some sms with different combinations of first two letters
• SBI sends sms as "BX-SBIINB", "TD-SBIINB" etc.

Some researching in internet points out that my observations about the last six letters are correct. The first two letters before the hyphen represents service provider and the region from which it is sent. For the examples above:

• "BX" = BSNL from Karnataka
• "TD" = Tata from Delhi

View the official list of bulk sms codes in the NDNC website.