How to find out if a given year is a leap year or not?

Well, for that, how do you define a leap year?
Leap year is every year the number of which is a multiple of four, except those devisible by 100 and not by 400.

Here are the steps to determine if a given year is a leap year or not:
if year modulo 400 is 0 then leap
    else if year modulo 100 is 0 then no_leap
    else if year modulo 4 is 0 then leap
    else no_leap

Here is one Perl implementation.

#!/usr/bin/perl
use strict;
use warnings;
###### is_leap_year ######
# Purpose : To determine whether a given year is a leap year or not
# Arguements : One
# First (Number): Year to be checked
# Returns : Boolean value indicating whether given year is a leap year or not
# true = given year is a leap year
# false = given year is not a leap year
############################
sub is_leap_year ($)
{
       my $year = shift;
       return unless ($year =~ m/^\d+$/);

       if (($year % 400) == 0) {
       # This year is completely divisible by 400
               return 1;     # This is a leap year
       }
       elsif (($year % 100) == 0) {
       # This year is completely divisible by 100
               return 0;     # This is not a leap year
       }
       elsif (($year % 4) == 0) {
       # This year is completely divisible by 4
               return 1;     # This is a leap year
       }
       return 0;     # This is not a leap year
}

my $this_year = 2040;
if (is_leap_year ($this_year)) {
       print $this_year, " is a leap year\n";
}
else {
       print $this_year, " is a not a leap year\n";
}

Count number of occurrences of a word

How can you count number of occurrences of a word in a file? Say, I want to count how many times ring is present in a file.

How about using the -c option of grep?
% grep -c ring /foo/bar

And what if the file contains words such as string and rings? That would break our count of ring.
Using the -w option of grep solves this problem
% grep -cw ring /foo/bar

What if the word ring is present more than once in a line? grep would produce incorrect count in this case, since it counts the number of lines in which the pattern is found. grep is not sufficient for this job. We need something that can count multiple occurrences of a word in a line.

To get the exact count:
#!/usr/bin/perl
# search_word.pl
my $search_this = shift or exit 1;
my $count = 0;
while (<>) {
    while (m/\b$search_this\b/g) {
        $count++;
    }
}
if ($count == 0) {
    print $ARGV . "does not contain " . $search_this . "\n";
}
else {
    print $ARGV . "contains " . $search_this . " " . $count . (($count == 1) ? " time\n" : " times\n");
}

Run this perl script as:
% perl search_word.pl ring filename

And what if I don't want to use Perl? Well, then this should work for you:
% grep -w -o ring /foo/bar | wc -l

Why not to use awk when sed can do the job?

• Using awk instead of sed has the price of performance and size
• compared to sed and ed, awk takes a substantially longer time to load, and does its job at a considerably slower pace
• The real distinguishing point between sed and awk as a text processor is that awk is able to work with a persistent context, whereas capabilities of sed in this area are limited to non-existent. If you - for instance - would have to sum one field to a total you would do it with awk (it would be possible to do it with sed, but would be a nightmare - poorly suited tool for the job)

Changing size of a file

How do you change the size of a file in Linux? If you are not concerned about the contents of the file, use the dd command.

dd if=/dev/zero of=/foo/bar bs=1024 count=1

This would change the size of a file to 1 KB. inode number of the file would be preserved.

So if you want to change the size to 2 MB

dd if=/dev/zero of=/foo/bar bs=1024 count=2048

Note that 2 MB is 2048 KB, and not 2000 KB.

Epigram on a Software Laird

Bless Linus Torvalds, O Engineer,
With grateful, lifted eyes,
Who taught that not the windows alone,
But doors too shall open;
For had He said "the doors alone
From source I will deliver,"
Alas, alas! O Engineer,
Then hadst thou lain for ever.

Original work: Epigram on a Country Laird by Robert Burns

Sorting alphanumeric strings in Perl

One of my friends had trouble sorting alphanumeric strings in Perl. Strings he had were similar to:

child1
child3
child11
child51
child5
child24

He wanted to sort them based on the numbers that follow after the alphabtic part. So, the order he wanted:

child1
child3
child5
child11
child24
child51

I extracted the numeric part from the alphanumeric string and used it for comparisons

@alphanumeric_sorted = sort { substr($a, 5) <=> substr($b, 5)} @alphanumeric;

Apache Lyrics

Sometime last year I wrote parody of a famous song. Some of the lines of this song are in Spanish, and you need to know a bit of Spanish to understand them.

"Ports Won't Die"
(feat. Office Assistant)

Macros up in here tonight
No fighting, no fighting
We got the fixes up in here
No fighting, no fighting

Apache, Apache

I never really knew that it could serve so fast
It makes a man wants to HTTP
Como se llama (si), bonita (si), mi OS (si, Apache Apache), su OS
Apache, Apache

Oh baby when you talk like that
You make IIS go mad
So be wise and keep on
Reading the signs of my Ballmer

And I'm on tonight
You know my ports won't die
And I'm starting to feel it's right
All the attraction, the tension
Don't you see baby, this is perfection

Hey Girl, I can see your traffic moving
And it's driving me crazy
And I didn't have the slightest idea
Until I saw you serving

And when you take up a bad request
Nobody cannot ignore the way you check it out, girl
And architecture so perfected - the way you right and left it
So you can keep on excelling

I never really knew that it could serve so fast
It makes a man want to HTTP
Como se llama (si), bonita (si), mi OS (si, Apache Apache), su OS
Apache, Apache

Oh baby when you talk like that
You make IIS go mad
So be wise and keep on
Reading the signs of my Ballmer

And I'm on tonight
You know my ports won't die
And I am starting to feel you boy
Come on lets go, real slow
Don't you see baby asi es perfecto

Oh I know I am on tonight my ports won't die
And I am starting to feel it's right
All the attraction, the tension
Don't you see baby, this is perfection
Apache, Apache

Oh boy, I can see your traffic moving
Half filtered, half cached
I don't, don't really know what I'm doing
But you seem to have a plan
My will and self restraint
Have come to fail now, fail now
See, I am doing what I can, but I can't so you know
That's a bit too hard to explain

Roca en el Internet toda la noche
Roca en el Internet toda el día

Roca en el Internet toda la noche
Roca en el Internet toda el día

I never really knew that it could serve so fast
It makes a man want to HTTP
Como se llama (si), bonita (si), mi OS (si, Apache Apache), su OS
Apache, Apache

Oh baby when you talk like that
You know you got me hypnotized
So be wise and keep on
Reading the signs of my Ballmer

Senorita, feel the conga, let me see you serve like you come from Redmond

Mira en Maryland se baila así, say it!
Mira en Maryland se baila así

Yeah
It's so popular, macro shaft's jealousy a refugee like me back with the Fugees from a buggy territory
I go back like when 'pac carried crates for Humpty Humpty
I need a whole club dizzy
Why the Court wanna break us?
Explorers and Windows
I ain't guilty, it's no monopoly transaction
No more do we snatch ropes
Refugees run the seas 'cause we own our own browser

I'm on tonight, my ports won't die
And I'm starting to feel you boy
Come on let's go, real slow
Baby, like this is perfecto

Oh, you know I am on tonight and my ports won't die
And I am starting to feel it's right
The attraction, the tension
Baby, like this is perfection

No fighting
No fighting