Update/move perl section (#187)

* New questions and spell check (#181) Added new questions related with KVM, Libvirt and DNF * Create a new perl folder and move the content of the actual section
2021-11-20 01:12:20 +01:00 · 2021-11-20 01:12:20 +01:00 · 764c7423b6
commit 764c7423b6
parent f772911c6a
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--- a/README.md
+++ b/README.md
@ -74,7 +74,7 @@
      <td align="center"><a href="#puppet"><img src="images/puppet.png" width="75px;" height="75px;" alt="puppet"/><br /><b>Puppet</b></a></td>
      <td align="center"><a href="#distributed"><img src="images/distributed.png" width="110px;" height="75px;" alt="Distributed"/><br /><b>Distributed</b></a></td>
      <td align="center"><a href="#questions-you-ask"><img src="images/you.png" width="90px;" height="75px;" alt="you"/><br /><b>Questions you can ask</b></a></td>
-      <td align="center"><a href="#perl"><img src="images/perl.png" width="75px;" height="75px;" alt="perl"/><br /><b>Perl</b></a></td>
+      <td align="center"><a href="exercises/perl/README.md"><img src="images/perl.png" width="75px;" height="75px;" alt="perl"/><br /><b>Perl</b></a></td>
  </tr>
 </table>
 </center>
@ -5034,518 +5034,6 @@ Output: 3
 [Golang container/heap package](https://golang.org/pkg/container/heap/)
 </b></details>
 ## Perl
 ### Perl Self Assessment
 <details>
 <summary>What is Perl?</summary><br><b>
 From the official [docs](https://perldoc.perl.org/):
 "Perl officially stands for Practical Extraction and Report Language, except when it doesn't."
 It's a general purpose programming language developed for manipulating texts mainly. It has been used to perform system administration tasks, networking, building websites and more.
 </b></details>
 <details>
 <summary>What data types Perl has? And how can we define it?</summary><br><b>
 - Scalar: This is a simple variable that stores single data items. It can be a string, number or reference.
 ```
 my $number = 5;
 ```
 - Arrays: This is a list of scalars. 
 ```
 my @numbers = (1, 2, 3, 4, 5);
 # or using the `qw` keyword (quote word):
 my @numbers = qw/1 2 3 4 5/; 
 # '/' can be another symbol, e.g qw@1 2 3 4 5@
 ```
 - Hashes (or associative arrays): This is an unordered collection of key-value pairs. We can access to a hash using the keys.
 ```
 my %numbers = (
  First => '1',
  Second => '2',
  Third => '3'
 );
 ```
 </b></details>
 <details>
 <summary>How can you access to a hash value, add and delete a key/value pair and modify a hash?</summary><br><b>
 ```
 my %numbers = (
  'First' => '1',
  'Second' => '2',
  'Third' => '3'
 );
 ```
 - Access:
 ```
 print($numbers{'First'});
 ```
 - Add:
 ```
 $numbers{'Fourth'} = 4;
 ```
 - Delete:
 ```
 delete $numbers{'Third'};
 ```
 - Modify:
 ```
 $numbers{'Fifth'} = 6;
 $numbers{'Fifth'} = 5;
 ```
 </b></details>
 <details>
 <summary>How can you iterate an array? And a hash?</summary><br><b>
 - Array:
 ```
 my @numbers = qw/1 2 3 4 5/;
 # Using `$_` that represents the current iteration in a loop. It starts from index array 0 until the last index.
 foreach (@numbers) {
    print($_);
 }
 # Output: 12345
 # "$#" returns the max index of an array. That's the reason because we can iterate accesing to the array from the index 0 to the max index.
 for my $i (0..$#numbers) {
    print($numbers[$i]);
 }
 # Output: 12345
 # Using the `map` keyword:
 print map {$_} @numbers;
 # Output: 12345
 # Using `while`. We should take care with this option. When we use `shift` we're deleting the first element of the array and assigning it to the `element` variable. 
 # After this `loop` the `numbers` array will not have elements.
 while (my $element = shift(@numbers)) {
    print($element);
 }
 # Output: 12345
 ```
 - Hashes:
 ```
 my %capital_cities = (
  'Madrid' => 'Spain',
  'Rome' => 'Italy',
  'Berlin' => 'Germany'
 );
 # Iterate and get the `keys`:
 foreach my $city (keys %capital_cities) {
    print($city . "\n");
 }
 # Iterate and get the `values`:
 foreach my $country (values %capital_cities) {
    print($country . "\n");
 }
 # Iterate and get the values and keys (first option):
 foreach my $city (keys %capital_cities) {
    print("City: $city - Country: $capital_cities{$city}" . "\n");
 }
 # Iterate and get the values and keys (first option):
 while(my ($city, $country) = each %capital_cities) {
    print("City: $city - Country: $capital_cities{$city}" . "\n");
 }
 ```
 </b></details>
 <details>
 <summary>What is a Perl subroutine? How to define it?</summary><br><b>
 It's the perl model for user defined functions (this is also called function like other programming languages). We can define a subroute with the keyword `sub`. 
 ```
 sub hello {
  print "hello";
 }
 ```
 </b></details>
 <details>
 <summary>Describe the different ways to receive parameters in a subroutine</summary><br><b>
 - List assignment: Using the `@_` array. It's a list with the elements that are being passed as parameters.
 ```
 sub power {
    my ($b, $e) = @_;
    return $b ** $e; 
 }
 &power(2, 3);
 ```
 - Individual assigment: We should access to every element of the `@_` array. It starts from zero.
 ```
 sub power {
    my $b = $_[0];
    my $e = $_[1];
    return $b ** $e; 
 }
 &power(2, 3);
 ```
 - Using `shift` keyword: It's used to remove the first value of an array and it's returned.
 ```
 sub power {
    my $b = shift;
    my $3 = shift;
    return $b ** $e; 
 }
 &power(2, 3);
 ```
 [Source](https://stackoverflow.com/a/21465275/12771230)
 We can also read the best way in the same S.O answer.
 </b></details>
 <details>
 <summary>What is lexical and dynamic scoping?</summary><br><b>
 </b></details>
 <details>
 <summary>How to apply referencing and dereferencing?</summary><br><b>
 </b></details>
 <details>
 <summary>Does Perl have conventions?</summary><br><b>
 You can check [perlstyle](https://perldoc.perl.org/perlstyle)
 </b></details>
 <details>
 <summary>What is Perl POD? Can you code an example?</summary><br><b>
 From the official [docs](https://perldoc.perl.org/perlpod):
 "Pod is a simple-to-use markup language used for writing documentation for Perl, Perl programs, and Perl modules."
 ```
 =item
    This function returns the factorial of a number.
    Input: $n (number you wanna calculate).
    Output: number factorial.
 =cut
 sub factorial {
    my ($i, $result, $n) = (1, 1, shift);
    $result = $result *= $i && $i++ while $i <= $n;
    return $result;
 }
 ```
 </b></details>
 ### Perl Regex
 <details>
 <summary>Check if the word `electroencefalografista` exists in a string</summary><br><b>
 ```
 my $string = "The longest accepted word by RAE is: electroencefalografista";
 if ($string =~ /electroencefalografista/) {                                                         
    print "Match!";
 }
 ```
 </b></details>
 <details>
 <summary>Check if the word `electroencefalografista` does not exists in a string</summary><br><b>
 ```
 my $string = "The longest not accepted word by RAE is: Ciclopentanoperhidrofenantreno";
 if ($string !~ /electroencefalografista/) {
    print "Does not match!";
 }
 ```
 </b></details>
 <details>
 <summary>Replace the word `amazing`</summary><br><b>
 ```
 my $string = "Perl is amazing!";
 $string =~ s/amazing/incredible/;
 print $string;
 # Perl is incredible!
 ```
 </b></details>
 <details>
 <summary>Extract `hh:mm:ss` with capturing group `()` in the following datetime</summary><br><b>
 ```
 my $date = "Fri Nov 19 20:09:37 CET 2021";
 my @matches = $date =~ /(.*)(\d{2}:\d{2}:\d{2})(.*)/;
 print $matches[1];
 # Output: 20:09:37
 ```
 </b></details>
 <details>
 <summary>Extract all the elements that are numbers in an array</summary><br><b>
 ```
 my @array = ('a', 1, 'b', 2, 'c', 3);
 my @numbers = grep (/\d/, @array);    # Note: \d involves more digits than 0-9
 map {print $_ . "\n" } @numbers;
 ```
 </b></details>
 <details>
 <summary>Print all the linux system users that starts with d or D</summary><br><b>
 - With a Perl one liner :D
 ```
 open(my $fh, '<', '/etc/passwd');
 my @user_info = <$fh>;
 map { print $& . "\n" if $_ =~ /^d([^:]*)/  } @user_info;
 close $fh;
 ```
 - Avoiding one-liners
 ```
 foreach my $user_line (@user_info) {
    if ($user_line =~ /^d([^:]*)/) {
        print $& . "\n";
    }
 }
 ```
 </b></details>
 ### Perl Files Handle
 <details>
 <summary>Mention the different modes in File Handling</summary><br><b>
 - Read only: `<`
 - Write mode. It creates the file if doesn't exist: `>`
 - Append mode. It creates the file if doesn't exist: `>>`
 - Read and write mode: `+<`
 - Read, clear and write mode. It creates the file if doesn't exist: `+>`
 - Read and append. It creates the file if doesn't exist: `+>>`
 </b></details>
 <details>
 <summary>How to write into a file?</summary><br><b>
 ```
 # We can use:
 # '>' Write (it clears a previous content if exists).
 # '>>' Append.
 open(my $fh, '>>', 'file_name.ext') or die "Error: file can't be opened";
 print $fh "writing text...\n";
 close($fh);
 ```
 </b></details>
 <details>
 <summary>How can you read a file and print every line?</summary><br><b>
 ```
 open(my $fh, '<', 'file_to_read.ext') or die "Error: file can't be opened";
 my @file = <$fh>;
 foreach my $line (@file) {
    print $line;
 }
 ```
 We can use the file handle without assigning it to an array:
 ```
 open(my $fh, '<', 'file_to_read.ext') or die "Error: file can't be opened";
 foreach my $line (<$fh>) {
    print $line;
 }
 ```
 </b></details>
 ### Perl OOP
 <details>
 <summary>Does Perl have support for OOP?</summary><br><b>
 From the official [docs](https://perldoc.perl.org/perlootut):
 "By default, Perl's built-in OO system is very minimal, leaving you to do most of the work."
 </b></details>
 <details>
 <summary>What is the purpose of the bless function?</summary><br><b>
 The function os the `bless` function is used to turning a plain data structure into an object.
 </b></details>
 <details>
 <summary>How to create a Perl class? How can you call a method?</summary><br><b>
 - Let's create the package: `Example.pm`
 ```
 package Example;
 sub new {
    my $class = shift;
    my $self = {};
    bless $self, $class;
    return $self;
 }
 sub is_working {
    print "Working!";
 }
 1;
 ```
 - Now we can instance the `Example` class and call `is_working` method:
 ```
 my $e = new Example();
 $e->is_working();
 # Output: Working!
 ```
 </b></details>
 <details>
 <summary>Does Perl have inheritance? What is the `SUPER` keyword?</summary><br><b>
 Yes, Perl supports inheritance. We can read about it in the official [docs](https://perldoc.perl.org/perlobj#Inheritance). 
 We also can read about `SUPER` keyword that is used to call a method from the parent class. It gives an example about how we can apply inheritance.
 </b></details>
 <details>
 <summary>Does Perl have polymorphism? What is method overriding?</summary><br><b>
 Yes, it has polymorphism. In fact method overriding is a way to apply it in Perl.
 Method overriding in simple words appears when we have a class with a method that already exist in a parent class.
 Example:
 ```
 package A;
 sub new { return bless {}, shift; };
 sub printMethod { print "A\n"; };
 package B;
 use parent -norequire, 'A';
 sub new { return bless {}, shift; };
 sub printMethod { print "B\n"; };
 my $a = A->new();
 my $b = B->new();
 A->new()->printMethod();
 B->new()->printMethod();
 # Output:
 # A
 # B
 ```
 </b></details>
 <details>
 <summary>How can you call a method of an inherited class?</summary><br><b>
 ```
 # Class `A` with `printA` method.
 package A;
 sub new { return bless {}, shift; };
 sub printA { print "A"; };
 # Class `B` that extends or use the parent class `A`.
 package B;
 use parent -norequire, 'A';
 sub new { return bless {}, shift; };
 # Instance class `B` allows call the inherated method
 my $b = B->new();
 $b->printA();
 ```
 </b></details>
 ### Perl OS
 <details>
 <summary>What is Perl Open3?</summary><br><b>
 </b></details>
 ### Perl Packages & Modules
 <details>
 <summary>What is a Perl package? And a module?</summary><br><b>
 </b></details>
 <details>
 <summary>What is the difference between .pl and .pm extensions?</summary><br><b>
 </b></details>
 <details>
 <summary>What is cpan? And cpanm?</summary><br><b>
 </b></details>
 <details>
 <summary>How can you install a Perl module?</summary><br><b>
 </b></details>
 ## Mongo
 <details>
--- a/exercises/perl/README.md
+++ b/exercises/perl/README.md
@ -0,0 +1,511 @@
 ## Perl
 ### Perl Self Assessment
 <details>
 <summary>What is Perl?</summary><br><b>
 From the official [docs](https://perldoc.perl.org/):
 "Perl officially stands for Practical Extraction and Report Language, except when it doesn't."
 It's a general purpose programming language developed for manipulating texts mainly. It has been used to perform system administration tasks, networking, building websites and more.
 </b></details>
 <details>
 <summary>What data types Perl has? And how can we define it?</summary><br><b>
 - Scalar: This is a simple variable that stores single data items. It can be a string, number or reference.
 ```
 my $number = 5;
 ```
 - Arrays: This is a list of scalars. 
 ```
 my @numbers = (1, 2, 3, 4, 5);
 # or using the `qw` keyword (quote word):
 my @numbers = qw/1 2 3 4 5/; 
 # '/' can be another symbol, e.g qw@1 2 3 4 5@
 ```
 - Hashes (or associative arrays): This is an unordered collection of key-value pairs. We can access to a hash using the keys.
 ```
 my %numbers = (
  First => '1',
  Second => '2',
  Third => '3'
 );
 ```
 </b></details>
 <details>
 <summary>How can you access to a hash value, add and delete a key/value pair and modify a hash?</summary><br><b>
 ```
 my %numbers = (
  'First' => '1',
  'Second' => '2',
  'Third' => '3'
 );
 ```
 - Access:
 ```
 print($numbers{'First'});
 ```
 - Add:
 ```
 $numbers{'Fourth'} = 4;
 ```
 - Delete:
 ```
 delete $numbers{'Third'};
 ```
 - Modify:
 ```
 $numbers{'Fifth'} = 6;
 $numbers{'Fifth'} = 5;
 ```
 </b></details>
 <details>
 <summary>How can you iterate an array? And a hash?</summary><br><b>
 - Array:
 ```
 my @numbers = qw/1 2 3 4 5/;
 # Using `$_` that represents the current iteration in a loop. It starts from index array 0 until the last index.
 foreach (@numbers) {
    print($_);
 }
 # Output: 12345
 # "$#" returns the max index of an array. That's the reason because we can iterate accesing to the array from the index 0 to the max index.
 for my $i (0..$#numbers) {
    print($numbers[$i]);
 }
 # Output: 12345
 # Using the `map` keyword:
 print map {$_} @numbers;
 # Output: 12345
 # Using `while`. We should take care with this option. When we use `shift` we're deleting the first element of the array and assigning it to the `element` variable. 
 # After this `loop` the `numbers` array will not have elements.
 while (my $element = shift(@numbers)) {
    print($element);
 }
 # Output: 12345
 ```
 - Hashes:
 ```
 my %capital_cities = (
  'Madrid' => 'Spain',
  'Rome' => 'Italy',
  'Berlin' => 'Germany'
 );
 # Iterate and get the `keys`:
 foreach my $city (keys %capital_cities) {
    print($city . "\n");
 }
 # Iterate and get the `values`:
 foreach my $country (values %capital_cities) {
    print($country . "\n");
 }
 # Iterate and get the values and keys (first option):
 foreach my $city (keys %capital_cities) {
    print("City: $city - Country: $capital_cities{$city}" . "\n");
 }
 # Iterate and get the values and keys (first option):
 while(my ($city, $country) = each %capital_cities) {
    print("City: $city - Country: $capital_cities{$city}" . "\n");
 }
 ```
 </b></details>
 <details>
 <summary>What is a Perl subroutine? How to define it?</summary><br><b>
 It's the perl model for user defined functions (this is also called function like other programming languages). We can define a subroute with the keyword `sub`. 
 ```
 sub hello {
  print "hello";
 }
 ```
 </b></details>
 <details>
 <summary>Describe the different ways to receive parameters in a subroutine</summary><br><b>
 - List assignment: Using the `@_` array. It's a list with the elements that are being passed as parameters.
 ```
 sub power {
    my ($b, $e) = @_;
    return $b ** $e; 
 }
 &power(2, 3);
 ```
 - Individual assigment: We should access to every element of the `@_` array. It starts from zero.
 ```
 sub power {
    my $b = $_[0];
    my $e = $_[1];
    return $b ** $e; 
 }
 &power(2, 3);
 ```
 - Using `shift` keyword: It's used to remove the first value of an array and it's returned.
 ```
 sub power {
    my $b = shift;
    my $3 = shift;
    return $b ** $e; 
 }
 &power(2, 3);
 ```
 [Source](https://stackoverflow.com/a/21465275/12771230)
 We can also read the best way in the same S.O answer.
 </b></details>
 <details>
 <summary>What is lexical and dynamic scoping?</summary><br><b>
 </b></details>
 <details>
 <summary>How to apply referencing and dereferencing?</summary><br><b>
 </b></details>
 <details>
 <summary>Does Perl have conventions?</summary><br><b>
 You can check [perlstyle](https://perldoc.perl.org/perlstyle)
 </b></details>
 <details>
 <summary>What is Perl POD? Can you code an example?</summary><br><b>
 From the official [docs](https://perldoc.perl.org/perlpod):
 "Pod is a simple-to-use markup language used for writing documentation for Perl, Perl programs, and Perl modules."
 ```
 =item
    This function returns the factorial of a number.
    Input: $n (number you wanna calculate).
    Output: number factorial.
 =cut
 sub factorial {
    my ($i, $result, $n) = (1, 1, shift);
    $result = $result *= $i && $i++ while $i <= $n;
    return $result;
 }
 ```
 </b></details>
 ### Perl Regex
 <details>
 <summary>Check if the word `electroencefalografista` exists in a string</summary><br><b>
 ```
 my $string = "The longest accepted word by RAE is: electroencefalografista";
 if ($string =~ /electroencefalografista/) {                                                         
    print "Match!";
 }
 ```
 </b></details>
 <details>
 <summary>Check if the word `electroencefalografista` does not exists in a string</summary><br><b>
 ```
 my $string = "The longest not accepted word by RAE is: Ciclopentanoperhidrofenantreno";
 if ($string !~ /electroencefalografista/) {
    print "Does not match!";
 }
 ```
 </b></details>
 <details>
 <summary>Replace the word `amazing`</summary><br><b>
 ```
 my $string = "Perl is amazing!";
 $string =~ s/amazing/incredible/;
 print $string;
 # Perl is incredible!
 ```
 </b></details>
 <details>
 <summary>Extract `hh:mm:ss` with capturing group `()` in the following datetime</summary><br><b>
 ```
 my $date = "Fri Nov 19 20:09:37 CET 2021";
 my @matches = $date =~ /(.*)(\d{2}:\d{2}:\d{2})(.*)/;
 print $matches[1];
 # Output: 20:09:37
 ```
 </b></details>
 <details>
 <summary>Extract all the elements that are numbers in an array</summary><br><b>
 ```
 my @array = ('a', 1, 'b', 2, 'c', 3);
 my @numbers = grep (/\d/, @array);    # Note: \d involves more digits than 0-9
 map {print $_ . "\n" } @numbers;
 ```
 </b></details>
 <details>
 <summary>Print all the linux system users that starts with d or D</summary><br><b>
 - With a Perl one liner :D
 ```
 open(my $fh, '<', '/etc/passwd');
 my @user_info = <$fh>;
 map { print $& . "\n" if $_ =~ /^d([^:]*)/  } @user_info;
 close $fh;
 ```
 - Avoiding one-liners
 ```
 foreach my $user_line (@user_info) {
    if ($user_line =~ /^d([^:]*)/) {
        print $& . "\n";
    }
 }
 ```
 </b></details>
 ### Perl Files Handle
 <details>
 <summary>Mention the different modes in File Handling</summary><br><b>
 - Read only: `<`
 - Write mode. It creates the file if doesn't exist: `>`
 - Append mode. It creates the file if doesn't exist: `>>`
 - Read and write mode: `+<`
 - Read, clear and write mode. It creates the file if doesn't exist: `+>`
 - Read and append. It creates the file if doesn't exist: `+>>`
 </b></details>
 <details>
 <summary>How to write into a file?</summary><br><b>
 ```
 # We can use:
 # '>' Write (it clears a previous content if exists).
 # '>>' Append.
 open(my $fh, '>>', 'file_name.ext') or die "Error: file can't be opened";
 print $fh "writing text...\n";
 close($fh);
 ```
 </b></details>
 <details>
 <summary>How can you read a file and print every line?</summary><br><b>
 ```
 open(my $fh, '<', 'file_to_read.ext') or die "Error: file can't be opened";
 my @file = <$fh>;
 foreach my $line (@file) {
    print $line;
 }
 ```
 We can use the file handle without assigning it to an array:
 ```
 open(my $fh, '<', 'file_to_read.ext') or die "Error: file can't be opened";
 foreach my $line (<$fh>) {
    print $line;
 }
 ```
 </b></details>
 ### Perl OOP
 <details>
 <summary>Does Perl have support for OOP?</summary><br><b>
 From the official [docs](https://perldoc.perl.org/perlootut):
 "By default, Perl's built-in OO system is very minimal, leaving you to do most of the work."
 </b></details>
 <details>
 <summary>What is the purpose of the bless function?</summary><br><b>
 The function os the `bless` function is used to turning a plain data structure into an object.
 </b></details>
 <details>
 <summary>How to create a Perl class? How can you call a method?</summary><br><b>
 - Let's create the package: `Example.pm`
 ```
 package Example;
 sub new {
    my $class = shift;
    my $self = {};
    bless $self, $class;
    return $self;
 }
 sub is_working {
    print "Working!";
 }
 1;
 ```
 - Now we can instance the `Example` class and call `is_working` method:
 ```
 my $e = new Example();
 $e->is_working();
 # Output: Working!
 ```
 </b></details>
 <details>
 <summary>Does Perl have inheritance? What is the `SUPER` keyword?</summary><br><b>
 Yes, Perl supports inheritance. We can read about it in the official [docs](https://perldoc.perl.org/perlobj#Inheritance). 
 We also can read about `SUPER` keyword that is used to call a method from the parent class. It gives an example about how we can apply inheritance.
 </b></details>
 <details>
 <summary>Does Perl have polymorphism? What is method overriding?</summary><br><b>
 Yes, it has polymorphism. In fact method overriding is a way to apply it in Perl.
 Method overriding in simple words appears when we have a class with a method that already exist in a parent class.
 Example:
 ```
 package A;
 sub new { return bless {}, shift; };
 sub printMethod { print "A\n"; };
 package B;
 use parent -norequire, 'A';
 sub new { return bless {}, shift; };
 sub printMethod { print "B\n"; };
 my $a = A->new();
 my $b = B->new();
 A->new()->printMethod();
 B->new()->printMethod();
 # Output:
 # A
 # B
 ```
 </b></details>
 <details>
 <summary>How can you call a method of an inherited class?</summary><br><b>
 ```
 # Class `A` with `printA` method.
 package A;
 sub new { return bless {}, shift; };
 sub printA { print "A"; };
 # Class `B` that extends or use the parent class `A`.
 package B;
 use parent -norequire, 'A';
 sub new { return bless {}, shift; };
 # Instance class `B` allows call the inherated method
 my $b = B->new();
 $b->printA();
 ```
 </b></details>
 ### Perl OS
 <details>
 <summary>What is Perl Open3?</summary><br><b>
 </b></details>
 ### Perl Packages & Modules
 <details>
 <summary>What is a Perl package? And a module?</summary><br><b>
 </b></details>
 <details>
 <summary>What is the difference between .pl and .pm extensions?</summary><br><b>
 </b></details>
 <details>
 <summary>What is cpan? And cpanm?</summary><br><b>
 </b></details>
 <details>
 <summary>How can you install a Perl module?</summary><br><b>
 </b></details>