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Perl is a high-level, general-purpose, interpreted programming language that was originally developed by Larry Wall in 1987. It borrows features from various other languages including C, shell scripting (sh), AWK, and sed. Perl is known for its flexibility and power, and it's commonly used for system administration, web development, network programming, GUI development and more. It supports both procedural and object-oriented programming. Perl also provides powerful text processing facilities without the arbitrary data-length limits of many contemporary Unix tools, facilitating manipulation of text files.

Ask the right questions secure the right Perl talent among an increasingly shrinking pool of talent.

First 20 minutes

General Perl app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Perl application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

What are scalar variables in Perl?

Scalar variables in Perl are single unit data like a number or a string. They are preceded by a dollar sign ($). For example, $name = 'John'; or $age = 30;

How would you declare an array in Perl?

In Perl, you declare an array using the @ symbol followed by the name of the array. For example, @names = ('John', 'Jane', 'Doe');

What is the difference between 'eq' and '==' in Perl?

'eq' is a string comparison operator, while '==' is a numeric comparison operator. 'eq' checks if the values of two strings are equal, while '==' checks if the values of two numbers are equal.

How would you use a hash in Perl?

A hash in Perl is an unsorted set of key-value pairs. You declare a hash using the % symbol. For example, %student = ('name' => 'John', 'age' => 20);

What are Perl packages?

Packages in Perl are used to create separate namespaces. This allows functions and variables with the same name to be used in different parts of the Perl script without conflict.

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What you’re looking for early on

Does the candidate have a strong understanding of Perl?

Has the candidate demonstrated problem-solving skills?

Is the candidate familiar with version control systems like Git?

Can the candidate work well in a team?

Next 20 minutes

Specific Perl development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

How would you open and read a file in Perl?

To open a file in Perl, you can use the 'open' function with the filename and mode as arguments. To read the file, you can use the '<>' operator in a while loop. For example, open(FILE, 'filename') or die 'Could not open file'; while() {print $_;}

Can you describe the difference between 'my' and 'local' in Perl?

'my' creates a new variable in the current scope, while 'local' temporarily changes the value of a variable in the current scope and its child scopes. 'my' variables are not accessible in subroutines while 'local' variables are.

What are Perl references and how would you use them?

References in Perl are the means of accessing or modifying the data of a variable, subroutine, or value indirectly. You can create a reference by using the backslash operator. For example, $ref = \$var; To access the value, you can use the $$ operator. For example, print $$ref;

How would you handle errors in Perl?

Errors in Perl can be handled using the 'eval' function. The 'eval' function catches exceptions and prevents the program from terminating. If an error occurs, it is stored in the $@ variable.

What is the difference between 'use' and 'require' in Perl?

'use' is a compile-time directive, while 'require' is a run-time directive. 'use' imports symbols and calls the import method, while 'require' only loads the module.

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At this point, a skilled Perl engineer should demonstrate strong problem-solving abilities, proficiency in Perl programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Perl.

What does the following Perl code do?
my $str = 'Hello, World!';
print reverse $str;
This code will print the string 'Hello, World!' in reverse order.
What will be the output of the following Perl code?
my @arr = (1, 2, 3, 4, 5);
print $arr[2];
This code will print the third element of the array which is '3'.
What does the following Perl code do?
my @arr = (1, 2, 3, 4, 5);
my @new_arr = map { $_ * 2 } @arr;
print @new_arr;
This code will print a new array where each element is twice the value of the corresponding element in the original array. The output will be '2 4 6 8 10'.
What does the following Perl code do?
use threads;
my $thr = threads->create(sub { print 'Hello, World!'; });
$thr->join();
This code creates a new thread that prints 'Hello, World!'. The 'join' function waits for the thread to finish execution.

Wrap-up questions

Final candidate for Perl Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Perl application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

How would you implement object-oriented programming in Perl?

Object-oriented programming in Perl can be implemented using packages. A package can be used as a class, and subroutines within the package can be used as methods. An object is an instance of a class, created using the 'bless' function.

What are regular expressions in Perl and how would you use them?

Regular expressions in Perl are a powerful tool for pattern matching and string manipulation. They are used with operators like =~ and !~. For example, if($str =~ /perl/) {print 'Match found';} else {print 'No match found';}

Can you describe the difference between 'grep' and 'map' in Perl?

'grep' and 'map' are both list processing functions. 'grep' is used to filter a list based on a certain condition, while 'map' is used to transform a list by applying a block of code to each element.

Perl application related

Product Perfect's Perl development capabilities

Beyond hiring for your Perl engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Perl projects, and can engage in multiple capacities.

Perl Consultive assessments

Perl Application Conversion Assessment Perl Application Integration Assessment Perl Data & Database Integration Assessment

Custom Perl development projects

Custom Perl App Conversion Perl Custom App Development Process App UI Design for Perl Facelifts

Hiring guide for Perl Engineers

Perl Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the Perl engineer at this point.

Perl Consultive assessments

Custom Perl development projects