Add new Perl questions (#184)
* New questions and spell check (#181) Added new questions related with KVM, Libvirt and DNF * New Perl questions * Change postition of topic in the table Put the perl topic at the end of the table to correct the table size
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README.md
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README.md
@ -74,6 +74,7 @@
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<td align="center"><a href="#puppet"><img src="images/puppet.png" width="75px;" height="75px;" alt="puppet"/><br /><b>Puppet</b></a></td>
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<td align="center"><a href="#distributed"><img src="images/distributed.png" width="110px;" height="75px;" alt="Distributed"/><br /><b>Distributed</b></a></td>
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<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>
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<td align="center"><a href="#perl"><img src="images/perl.png" width="75px;" height="75px;" alt="perl"/><br /><b>Perl</b></a></td>
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</tr>
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</table>
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</center>
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@ -5033,6 +5034,294 @@ Output: 3
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[Golang container/heap package](https://golang.org/pkg/container/heap/)
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</b></details>
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## Perl
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### Perl Self Assessment
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<details>
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<summary>What is Perl?</summary><br><b>
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From the official [docs](https://perldoc.perl.org/):
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"Perl officially stands for Practical Extraction and Report Language, except when it doesn't."
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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.
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</b></details>
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<details>
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<summary>What data types Perl has? And how can we define it?</summary><br><b>
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- Scalar: This is a simple variable that stores single data items. It can be a string, number or reference.
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```
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my $number = 5;
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```
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- Arrays: This is a list of scalars.
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```
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my @numbers = (1, 2, 3, 4, 5);
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# or using the `qw` keyword (quote word):
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my @numbers = qw/1 2 3 4 5/;
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# '/' can be another symbol, e.g qw@1 2 3 4 5@
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```
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- Hashes (or associative arrays): This is an unordered collection of key-value pairs. We can access to a hash using the keys.
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```
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my %numbers = (
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First => '1',
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Second => '2',
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Third => '3'
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);
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```
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</b></details>
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<details>
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<summary>How can you access to a hash value, add and delete a key/value pair and modify a hash?</summary><br><b>
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my %numbers = (
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'First' => '1',
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'Second' => '2',
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'Third' => '3'
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);
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- Access:
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print($numbers{'First'});
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- Add:
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$numbers{'Fourth'} = 4;
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- Delete:
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delete $numbers{'Third'};
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- Modify:
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$numbers{'Fifth'} = 6;
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$numbers{'Fifth'} = 5;
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</b></details>
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<details>
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<summary>How can you iterate an array? And a hash?</summary><br><b>
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- Array:
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```
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my @numbers = qw/1 2 3 4 5/;
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# Using `$_` that represents the current iteration in a loop. It starts from index array 0 until the last index.
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foreach (@numbers) {
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print($_);
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}
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# Output: 12345
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# "$#" 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.
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for my $i (0..$#numbers) {
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print($numbers[$i]);
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}
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# Output: 12345
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# Using the `map` keyword:
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print map {$_} @numbers;
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# Output: 12345
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# 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.
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# After this `loop` the `numbers` array will not have elements.
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while (my $element = shift(@numbers)) {
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print($element);
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}
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# Output: 12345
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```
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- Hashes:
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```
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my %capital_cities = (
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'Madrid' => 'Spain',
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'Rome' => 'Italy',
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'Berlin' => 'Germany'
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);
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# Iterate and get the `keys`:
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foreach my $city (keys %capital_cities) {
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print($city . "\n");
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}
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# Iterate and get the `values`:
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foreach my $country (values %capital_cities) {
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print($country . "\n");
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}
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# Iterate and get the values and keys (first option):
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foreach my $city (keys %capital_cities) {
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print("City: $city - Country: $capital_cities{$city}" . "\n");
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}
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# Iterate and get the values and keys (first option):
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while(my ($city, $country) = each %capital_cities) {
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print("City: $city - Country: $capital_cities{$city}" . "\n");
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}
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```
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</b></details>
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<details>
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<summary>What is a Perl subroutine? How to define it?</summary><br><b>
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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`.
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```
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sub hello {
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print "hello";
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}
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```
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</b></details>
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<details>
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<summary>Describe the different ways to receive parameters in a subroutine</summary><br><b>
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- List assignment: Using the `@_` array. It's a list with the elements that are being passed as parameters.
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```
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sub power {
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my ($b, $e) = @_;
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return $b ** $e;
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}
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&power(2, 3);
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```
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- Individual assigment: We should access to every element of the `@_` array. It starts from zero.
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```
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sub power {
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my $b = $_[0];
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my $e = $_[1];
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return $b ** $e;
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}
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&power(2, 3);
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```
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- Using `shift` keyword: It's used to remove the first value of an array and it's returned.
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```
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sub power {
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my $b = shift;
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my $3 = shift;
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return $b ** $e;
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}
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&power(2, 3);
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```
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[Source](https://stackoverflow.com/a/21465275/12771230)
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We can also read the best way in the same S.O answer.
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</b></details>
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<details>
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<summary>What is lexical and dynamic scoping?</summary><br><b>
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</b></details>
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<details>
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<summary>How to apply referencing and dereferencing?</summary><br><b>
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</b></details>
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<details>
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<summary>Does Perl have conventions?</summary><br><b>
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You can check [perlstyle](https://perldoc.perl.org/perlstyle)
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</b></details>
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<details>
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<summary>What is Perl POD? Can you code an example?</summary><br><b>
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From the official [docs](https://perldoc.perl.org/perlpod):
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"Pod is a simple-to-use markup language used for writing documentation for Perl, Perl programs, and Perl modules."
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```
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=item
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This function returns the factorial of a number.
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Input: $n (number you wanna calculate).
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Output: number factorial.
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=cut
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sub factorial {
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my ($i, $result, $n) = (1, 1, shift);
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$result = $result *= $i && $i++ while $i <= $n;
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return $result;
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}
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```
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</b></details>
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### Perl Regex
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<details>
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<summary>How do you perform regular expresions in Perl?</summary><br><b>
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</b></details>
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### Perl Files Handle
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<details>
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<summary>How to write into a file?</summary><br><b>
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</b></details>
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### Perl OOP
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<details>
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<summary>Does Perl have support for OOP?</summary><br><b>
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From the official [docs](https://perldoc.perl.org/perlootut):
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"By default, Perl's built-in OO system is very minimal, leaving you to do most of the work."
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</b></details>
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<details>
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<summary>What is the purpose of the bless function?</summary><br><b>
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The function os the `bless` function is used to turning a plain data structure into an object.
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</b></details>
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<details>
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<summary>Does Perl have inheritance?</summary><br><b>
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</b></details>
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<details>
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<summary>Does Perl have polymorphism? What is method overriding?</summary><br><b>
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</b></details>
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### Perl OS
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<details>
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<summary>What is Perl Open3?</summary><br><b>
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</b></details>
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### Perl Packages & Modules
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<details>
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<summary>What is a Perl package? And a module?</summary><br><b>
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</b></details>
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<details>
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<summary>What is the difference between .pl and .pm extensions?</summary><br><b>
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</b></details>
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<details>
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<summary>What is cpan? And cpanm?</summary><br><b>
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</b></details>
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<details>
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<summary>How can you install a Perl module?</summary><br><b>
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</b></details>
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## Mongo
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<details>
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