Perl Interview Questions

What is Perl?

Perl is an open-source programming language that is widely used. It includes a wide variety of libraries, resources and programmers used for a variety of tasks associated with web development, practical extraction, network programming, system administration, reporting language, GUI development, and other bulk text processing tasks. PERL is more trending today because of its fast development cycle and its text manipulation capabilities.

What are the features of PERL?

PERL contains integrated regular expressions that are efficient in data transformation and filtration.

• Learning Perl is simple and easy.
• Only one script may be used on more than one device.
• Assists web data encryption that includes e-commerce transactions.
• DBI package support for ease of web database integration.
• Procedural, Unicode, as well as object-oriented language support.
• SWIG and XS are suitable for Perl interfaces with external C or C++ libraries.
• Platform independent
• Perl is a kind of request-response language.

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Why should we choose Perl as a scripting language?

Reasons for choosing PERL as a scripting language are as follows:

• A single line of Perl code is the equivalent of multiple line codes in any other language.
• Only one script could be used on more than one device.
• There is no need to implement the logic as in C or Python.
• It includes an enormous integrated parsing interpreter, pattern matching as well as regular expression.

What kinds of Perl variables are available?

The variables that are used in Perl are as follows:

• Arrays 
• Hashes
• Scalars

What are the types of operators used in Perl?

The following are the Perl operator types:

• Assignment operators
• Bitwise operators
• Comparison operators
• Logical operators
• Numeric operators
• Special operators
• String operators

What are the array functions within Perl?

The array function is used for adding or deleting elements. This feature can be used in 4 different types.

Pop: It removes the last element from an array.

Push: It is used to add a new element at the end of an array.

Shift: It is used to delete the element at the left of an array.

Unshift: It is used to add a new element at the beginning of an array.

What type of Scalar functions are used in Perl?

Following are the types of Scalar functions used in Perl:

• Defined
• Chomp
• Chop
• Index
• Ref
• Reverse
• Return
• Undef

What kind of hash functions are used in Perl?

• Context
• Delete
• Exists
• Each
• Hash length
• Keys
• Sort
• Values

Is Perl an interpreter or a compiler?

The Perl programming language can be used as a compiler as well as an interpreter at the same time. It takes the source code and converts it into the bytecode that the programming language can understand. After that, we can execute and run the program. Therefore the Perl programming language is considered as an interpreter and compiler at the same time.

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) What is the @ARGV array?

The @ARGV array is a special array for storing the command line argument. Its work is identical to the normal array. That is, the first and second arguments will be given as $ARGV[0] and $ARGV[1].

) What is dereferencing?

Dereferencing Returns the value to the location from a reference point. For dereferencing a reference, we may use @, $ or % as the prefix to the reference variable.

) What is memory management?

When a Perl variable is used by the programmers, some memory will be occupied. Users should ensure that the memory is used as effectively as possible. After running a program, files can be divided into sections and can be managed easily.

) What is CPAN?

CPAN refers to the Comprehensive Perl Archive Network. It is an extensive collection of all software and documents associated with Perl. Programmers can access it and avoid the challenges they are experiencing. It is very useful for programmers, and they can obtain a lot of useful information.

) What is a Subroutine?

The subroutine is a block of code that is used in the Perl programming language. It is implemented together to allocate a task. It may be performed at any time within a program. One of its benefits is that it assists in running modular programming, making it easier to understand. It removes duplication of all programs that reuses the same code within the programming language.

) What is debugging?

All the programmers are aware of debugging. In fact, numerous errors report their presence in the programs for reasons that are not always required to be known accurately. The elimination of such errors is very important for the smooth running of tasks. Finding these errors or bugs is called debugging. Programming languages may have built-in debugger options, or programmers may want to consider other options as well.

) Explain database connectivity in Perl.

The first step is to use DBI module.

my $dbh = DBI -> connect('dbi:Oracle:orcl', 'username', 'password',)

Where we will be able to use our username and password.

Then the database handler object's prepare() method is used, which will accept the SQL statement as the argument.

Finally, execute the query with the help of the execute() method.

) What are the differences between die and exit in Perl?

Die displays an error message when exit fails to do so.

Die will always accept the string or nothing but does not accept any number as an argument.

) How does gmtime() differ from the localtime() function?

) List some arguments that are commonly used in Perl.

Some of the arguments that are commonly used in Perl are:

-c denotes a non-return compilation

-d stands for debug

-e stands for execution

-w indicates a warning

) When do we use -l, -p and -n options?

We use -n, -p to include scripts in the loops. -l gives the programming language the ability to implement the script in the loop. The –p options operate similarly with the continuation addition. –i option changes the files where appropriate. By using this option, the input file name can be modified, and the output file opens with the name of the original file. This option does not create a backup of the files.

) How important are Perl warnings?

To verify the quality of any language encoding, warnings are the basic methods for checking the incorrect codes. At the lexical analysis stage, certain common mandatory issues are highlighted. As a result, the time spent searching for weird results is very high and can be minimized by activating warnings. There are a number of ways in which warnings can be activated. 

On the command line for the Perl one-liner, the -w option is used. It is also used on the Shebang line on OS like Windows or UNIX. Windows Perl requires no warnings. For a different operating system, we need to select the compiler warnings.

) How can we insert the information into the hashes in Perl?

There is no literal representation of what a hash contains. Users need to ensure that the hash is unwinding before it is indeed filled with the data. Value pairs may be easily created and converted afterwards. During the conversion process, hashes are randomly selected.

A hash represents a set of key values. On the right, even number items are listed that are known as values, and the ones which are on the left side are known as Keys. They are scalable values. After a % sign hashes are used and by assigning a value to it, it can be created. To incorporate the information in the hashes, we need to create key-value pairs, which is called the unwinding of hash.

) How can we use modules?

Generally, a module refers to a namespace which is specified in a file. Modules indicate a collection of some guidelines and functions that need to be followed while implementing them in Perl.  

• The assigned filename must be identical to the package name.
• The package name must begin with an uppercase letter.
• File names must include "pm" as the extension.
• If no object-oriented technique is implemented, the package must be derived from the Exporter class. 
• For non-object techniques that are used within modules, variables and functions must be derived from the namespace using the arrays @EXPORT and @EXPOR_OK.

) What is the difference between the Perl array and the Perl hash?

Perl array: It is an ordered list of elements that index numbers use. It is represented by a @sign. 

Perl hash: It is an unordered list of elements that key values use. It is represented by a %sign.

) What are the types of primary data structures?

In Perl scripting Language, there are three primary data structures. They are:

Arrays: It is represented by @ symbol.

Scalars: It can hold one piece of information at a time. It is represented by a $ symbol. Moreover, the $ symbol is followed by an identifier which will be alphanumeric or underscore. It cannot start with a number.

Associative arrays: Associative arrays are also called hashes. They work the same way hash tables of other programming languages work.

) what is the difference between use and require?

Use and Require both are used to import modules. A file extension is not necessary for either of them. For use, The objects that are included are different during compilation. For Require, the objects are checked at the time of runtime.

) What is the difference between My and Local?

) Does Perl programming include objects or not?

Yes, the Perl programming language has objects which do not require it to be used. In most of the cases, it is possible to use object-oriented modules that do not even understand the object. However, if the program is large, it must be subject-oriented.

) What do you mean by subroutine?

It is a block of code that is used in the Perl programming language that is implemented to assign a task. It may be executed at any time within a program. It assists in running modular programming, making it easier to understand. It helps to remove duplication of any program that reuses the same code within the programming language.

) How can we use Perl for implementing the tail function in Unix?

We need to keep a structure for storing the file size and line number at that time, for example, 1-10 bytes, 2-18 bytes. We will have a counter to increase the number of lines for finding the number of rows within the file. After you have finished the file, We will know the file size at the nth line, use 'sysseek' to bring the file pointer to this position, then begin reading to the end.

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) What is meant by Perl Identifier?

Ans. A Perl Identifier helps identify a variable, class, function, module, or other related objects while using this coding language. The variable name begins with a symbol such as $, @, %, etc., followed by digits and an underscore.

) What types of data are supported by Perl?

Ans. Perl supports three types of data: Scalars, Arrays of Scalars, and Hashes of Scalars. 

) How do you convert an array into a string in Perl?

Ans. The Perl join array function is used to convert an array into a string in Perl. 

) What is meant by Hash?

Ans. A Perl hash is a set of key-value pairs preceded by the symbol percent (%). Each key is unique in the Perl hash structure and of type string. 

) Define variable context in Perl.

Ans. In terms of context or situation, Perl manages the variable differently.

) Distinguish between Perl List and Perl Array.

Ans. The Perl List is a process of bringing data into the Perl source code, which includes a fixed collection of Scalars. It is present in a one-dimensional form. Perl array collects and stores data in the form of variables, and these arrays are multi-dimensional. 

) Is it possible to load binary extensions dynamically?

Ans. Yes, it's possible to load binary extensions if the system supports the same dynamically. Otherwise, you can statically compile the extensions to make it possible.

) What is meant by file handling in Perl?

Ans. In Perl, file handles are internal structures related to the file names. A File Handler in Perl allows access to files like text, logs, etc. It is similar to a connection helpful to change the file contents and is named for faster access. Moreover, Perl file handles are beneficial for reading, writing, opening, and closing. 

) Define the various File Handles in Perl.

Ans. There are three basic file handles in Perl such as-

STDIN - It refers to Standard Input in Perl and is useful to read from the keyboard.

STDOUT - It refers to Standard Output in Perl and is helpful to write into the screen or a program.

STDERR - A Standard Error stream in Perl helpful to write into the screen.

) How do you create and open a directory in Perl?

Ans. To build a new directory in Perl, we use the "mkdir" function, which needs permission to create. To open a directory, we use the "opendir" function, which returns True if it is successful; otherwise, it returns false.

) How can you add a module file in Perl?

Ans. It is possible to add a Module file in Perl using the following functions- "Require," "Use," and "Or."

) How can you empty an array in Perl?

Ans. It is easy to empty an array in Perl. It requires setting the array value to zero, and by allocating a null list to the same, users can execute this task. 

) Name the function used to read a directory in Perl.

Ans. We use the "readdir" function to read a directory in Perl. 

) Define chomp() function in Perl.

Ans. In Perl, the Chomp() is an essential function that removes the last newline character from the string's input. Also, we can use it to remove the newline character from the end of the string.

) How to use Closure in Perl?

Ans. In Perl, a block of code captures the lexical (linguistic) variables that a block holds. It uses it in the outer environment.

) Define Perl one-liner.

Ans. One-liners in Perl are command-line programs that can be executed from the command line right away. Writing effective code in a single line is easy for faster execution is possible through one-liners. 

) Define the use of the Perl grep() function.

Ans. Grep() is an essential function in Perl and helps recover an element from the array. It filters the list and returns the details only that match the criteria set by the users on the function.

) What is meant by Lexical variables in Perl?

Ans. These variables are used in many cases and are created using the "my" keyword or operator. Also, these variables are private in nature.

) Why use Perl Scripting?

Ans. Perl scripting is used in many fields, including web development and automating tasks in a web server. We can use it for data extraction and producing various reports through text processing. Perl also supports operating systems and multiple modules. It is also helpful in creating and manipulating images.

) What are the benefits of using the Perl scripting language?

Ans. 

• Perl uses simple syntax, and it is easy to use and understand.
• It supports object-oriented programming.
• It supports many platforms and markup languages like HTML, XML, etc. 
• Perl scripting language is very flexible to use.
• Perl is an interpreted language.

) What is the use of the undef function in Perl scripting?

Ans. The function "undef" is useful to undefine the value of the variables. The value is considered Null. When a programmer states a scalar variable and doesn't assign a value to the same, it is assumed to include an "undef" value.

) Name the different Loop control keywords in Perl.

Ans. There are three different Loop control keywords in Perl.:-

• Next
• Last
• Redo

) Define

Ans. It is also called Strict pragma, which helps find bugs or errors in the script and stops the program's execution. The pragma forces a developer to code so that it executes correctly, making the program error-free.

) Can we store Compiled Form as a File in Perl?

Ans. No, we cannot store a compiled form as a file.

) What is meant by Perl Strings?

Ans. In Perl, strings are an important part of Scalars, beginning with a $ sign. We can place Strings within a single or a double quote. There are two types of String operators in Perl-

• Concatenation (.)
• Repetition (x)

) What is the use of the Chop function in Perl?

Ans. The chop function is used to avoid some random characters from the expression or to delete the last character from the input string. 

) Define interpolation in Perl.

Ans. Interpolation in Perl refers to replacing the variables with its value.

) How can we compare two strings in Perl?

Ans. To compare two different strings in Perl, we use the "eq" operator, which checks the equality of lines. 

) Define the Split function and Join function in Perl.

Ans. Split() is a string function in Perl that helps split a string into different pieces using -, \, etc. The join function allows combining a list's elements into a single string. It uses the VAR value to split each element. 

) What is a Regular Expression in Perl?

Ans. A regular expression in Perl is a string of characters or a unique text string that defines a particular pattern. The following are the regular expression operators used in Perl-

• Matching
• Substitute
• Transliterate