First Up On the Block - Perl

The first{block}list subroutine, as stated above, returns the first value in a list. If you have a list that contains the following data, in this order: Hercules, Perseus, Theseus, and Mister T (basically a list of Greek heroes) and you use the first{block}list subroutine on it, then your result would be: Hercules. This is because he is the first piece of data in the list. Don't believe it? Let's go to the code:

#!/usr/bin/perl

use List::Util qw(first);

@Greek=('Hercules','Perseus','Theseus','Mister T');

$Front = first {$_} @Greek;

print $Front;

The result?

  Hercules

We can do the same with numbers:

#!/usr/bin/perl

use List::Util qw(first);

@Nums=(1,2,3,4);

$Front = first {$_} @Nums;

print $Front;

Which results in:

  1

But what if we don't want just the first value in a list? What if we want to set certain criteria that must be met? We can do so by adding conditionals to our subroutine:

#!/usr/bin/perl

use List::Util qw(first);

@Nums=(1,2,3,4);

$Front = first {$_>2} @Nums;

print $Front;

In the above code, we modify the parameter by adding a greater than two conditional. Simply put, we want the first value larger than the number 2. The result, of course, is:

  3

And likewise, we can also use things like AND and OR as well:

#!/usr/bin/perl

use List::Util qw(first);

@Nums=(1,2,3,4);

$Front = first {$_<5 && $_>3} @Nums;

print $Front;

Here, we use the following criteria: less than five, yet greater than three. This returns the number four.