Perl Weekly Challenge 72: trailng zeros and line filter

One way to let me improve my knowledge about Raku (aka Perl 6) is to implement programs in it. Unluckily, I don’t have any production code to implement in Raku yet (sob!). So, why not try solving the Perl Weekly Challenge tasks?

In the following, the assigned tasks for Challenge 72.


The general situation about the COVID is pretty much the same as the last week. It is still not clear to me what will happen to schools, and I really hope my kid will get the chance to return to school in a decent way.


She is trying to make some trouble again, and this is somewhat comfortating. However, she cannot jump nothing higher than a chair.
I’ve kept her in the garden for a few hours, but tied with the dog tie. At least, she is taking some fresh air and getting to know the external world again.


I’m running out of medicines at in a fast time. Besides, no great news, I need to wait for the surgery.

PWC 72 - Task 1

The first task was quite easy: counting the trailing zeros in a factorial of a number.
My five-minutes solution is the following:

sub MAIN( Int $N where { 0 < $N <= 10 } ) {
    my $factorial = [*] 1 .. $N;
    my $zeros = $factorial ~~ / 0+ $ /;
    "$N ! = $factorial and has { $zeros.chars } trailing zeros".say;

Computing the factorial is simple, thanks to the reduction [*] operator. Then I applied a regular expression to match any trailing zero, and then ask to the Match object how many chars the match find out.

PWC 72 - Task 2

The second task was the implementation of something similar to the head(1) command: filtering lines within a range.
I decided to use a counter to find the first line:

sub MAIN( Str $file-name,
          Int $A where { $A > 0 },
          Int $B where { $B >= $A } ) {
    my $line-counter = 0;
    for $file-name.IO.lines -> $line {
        $line.say if ( $A <= ++$line-counter <= $B );

For every $line I print it only if the $line-counter is within the defined range of lines.
There is a chance to get a smarter approach, I thought about playing with nl-in, but it does suffice to remember that IO.lines is lazy and you can store it in an array to get the lines you need:

my @lines = $file-name.IO.lines;
@lines[ $A .. $B ].join( "\n" ).say;

The article Perl Weekly Challenge 72: trailing zeros and line filter has been posted by Luca Ferrari on August 3, 2020