Perl

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Tutorials

Scalars

my $string = 'text';
my $integer = 42;
my $float = 3.14;

say $string;
say $integer;
say $float;

• Functions
  

  Functions for SCALARs or strings | perldoc.perl.org

  • substr
  • index
  • chomp

Arrays

• Fundamental operations
  

  # Declare array
  my @elements = ('one', 'two', 'tree', 'four');
  
  # Access elements
  say $elements[0];
  say $elements[1];
  say $elements[2];
  say $elements[3];
  
  # Get array size
  say 'Number of elements: ' . @elements;
  

  See http://modernperlbooks.com/books/modern_perl_2014/03-perl-language.html#QXJyYXlBc3NpZ25tZW50

• Element manipulation
  
  • pop: remove and return the last element
  • shift: remove and return the first element
  • push: add element(s) at the tail
  • unshift: add element(s) at the top

  See http://perlmaven.com/manipulating-perl-arrays

• Sort elements
  

  Sort acending:

  my @ascending_sorted_list = sort {$a <=> $b} @original_list;
  

  Sort descending:

  my @descending_sorted_list = sort {$b <=> $a} @original_list;
  

  Using a custom sort function:

  sub cmp_value {
      return $a <=> $b;
  }
  
  my @sorted_elements = sort cmp_value @elements;
  

  See http://perldoc.perl.org/functions/sort.html

• Functions
  

  http://perldoc.perl.org/index-functions-by-cat.html#Functions-for-real-@ARRAYs

  • grep
  • join: Create a string out of an array
  • map
  • qw//
  • reverse
  • unpack
• Read more
  
  • http://perldoc.perl.org/index-functions-by-cat.html#Functions-for-real-@ARRAYs
  • http://modernperlbooks.com/books/modern_perl_2014/03-perl-language.html#YXJyYXlz

Hashes

• Functions
  

  http://perldoc.perl.org/index-functions-by-cat.html#Functions-for-real-%25HASHes

References

• Basic example
  

  my %combination;
  
  $combination{25} = 0;
  $combination{10} = 0;
  $combination{ 5} = 0;
  $combination{ 1} = 0;
  $combination{25} += 3;
  
  my $cref = \%combination;
  $cref->{25} -= 1;
  say Dumper(%combination);
  

• How to dereference a list?
  

  my @list = (25, 20, 5, 1);
  my $list_ref = \@list;
  for my $element (@{$list_ref})
      say $element;
  }
  

• How to dereference a hash reference?
  
  • http://perldoc.perl.org/perlreftut.html#Using-References

Constants

use constant US_COINS => {
    QUARTERS => 25,
    DIMES    => 10,
    NICKELS  => 5,
    PENNIES  => 1
};

for my $name (keys US_COINS) {
    say $name;
}

say US_COINS->{'QUARTERS'};

Conditionals

my $false_1 = 0;
my $false_2 = '0';
my $false_3 = '';
my $false_4 = ();
my $false_5 = undef;
my $true = 'rest';

if ($false_1) {
    say 'if block executed';
} elsif ($true) {
    say 'elsif block executed';
} else {
    say 'else block executed';
}

Loops

• while
  

  my @list = ('one', 'two', 'three');
  while (@list) {
      say shift @list;
  }
  

• for
  

  http://perldoc.perl.org/perlsyn.html#For-Loops This is the Perl way for for-loops:

  for (1..10) {
      say 'Counter: ' . $_;
  }
  

  However, C-style loops could be used as well:

  for (my $i = 0; $i < 10; $i++) {
      say 'Counter: ' . ($i + 1);
  }
  

• foreach
  

  For and foreach can be used as synonyms.

• Labels and continue
  

  while, until and for loops support labels in order to control the loop execution.

Functions

How to export a function from a module?

• Default parameters
  

  http://modernperlbooks.com/books/modern_perl_2014/04-perl-operators.html#TG9naWNhbE9wZXJhdG9ycw

  sub function {
      my ($var_1, $var_2) = @_;
  
      $var_2 = $var_2 // 42;
      say $var_1;
      say $var_2;
  }
  
  function('test', '84');
  

Packages

package Local::Anagrams;

use strict;
use warnings;
use Exporter 'import';
our @EXPORT_OK = qw/ get_permutations /;

sub get_permutations
    my $string = shift;
    # ...
    return @permutations;
}

1;

How to extract information from a string?

How to compare strings?

if ($var eq "text") {
    print '$var equals "text"';
}

How to replace a substring?

How to write files?

How to read file contents?

Terminal

Test::Simple

use strict;
use warnings;

use Test::Simple tests => 1;

sub add {
    my ($a, $b) = @_;
    return $a + $b;
}

ok(add(1,2) == 3, 'Simple addition calculated correctly.');

Test::More

use strict;
use warnings;
use Test::More tests => 2;
use Local::List;
my @example_list = (6,1,34,3,12);
my $min_value = min(@example_list);
cmp_ok($min_value, '==', 1);
my $max_value = max(@example_list);
cmp_ok($max_value, '==', 34)

Test::Class

Exception testing

Read more

Math::Round

use strict;
use warnings;

use Math::Round; #http://search.cpan.org/~grommel/Math-Round-0.06/Round.pm

my $f = 3.1415926535;
my $r = printf("%.3f", 3.1415926535);
print "$r\n";

POSIX

use strict;
use warnings;

use feature 'say';
use POSIX qw (floor ceil);

my $float = 1.234;
say floor($float);
say ceil($float);
# https://metacpan.org/pod/distribution/perl/ext/POSIX/lib/POSIX.pod