Perl Interview Questions and Answers

Perl interview questions

PERL is the acronym for Practical Extraction and Reporting Language. It was developed by Larry Wall in 1987. It is a free open source language that supports object-oriented language like C++. PERL is a high-level, dynamic programming language licensed under General Public License (GNU) and is quite simple to learn as its syntax is similar to C.

The first version of PERL was 1.0 which was developed in December 1987 when Larry Wall was working as a developer in Unisys. Gradually, PERL 2 was developed in 1988 as a better version of the previous one, and PERL 3 was developed in 1989 which showed added support for binary data streams. PERL is a sensitive programming language and works with several other markup languages. The nature of PERL is procedural and supports object-oriented programming.

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The market has a huge potential in the field of PERL programming. More and more avenues are being opened as a PERL programmer and if you want to excel in your career as a PERL programmer, then cracking the PERL interview is a must. We’ve listed important PERL interview questions that will make you ready for your next interview. Prepare for them and be ready to ace your interview.

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Perl interview questions

The functions that allow us to include a module file or a module is the “use” and “require” function. The differences between the two are:
  1. The “use” function is used for loading the module at the compile time whereas the “require” function is used for loading the module at the runtime.
  2. “Use” calls the import function of modules inbuilt whereas “require” calls the import module separately.
  3. The “use” function is used only for the modules and that too for including .pm type file. The “require” function is used for both the libraries and modules.
  4. In “use,” we are not required to specify the file extension whereas in “require,” it is mandatory to specify the file extension.
Perl data types are treated differently based on the context in which they are accessed. They are-
  • Scalar Context: It accesses data items as scalar values. Scalar context can be further divided into string context, numeric context and don’t-care context. Scalar context simply returns the whatever kind of scalar value they want to and let PERL convert numbers to strings in string context and strings to numbers in numeric context. Sometimes, the scalar contexts don’t care whether a string, number or a reference is returned, so no conversion happens in that case.
  • List Context: It treats the lists and hashes as atomic objects. Assignment to an array or a hash evaluates the right-hand side in the list context.
  • Boolean Context- It is a place where an expression is evaluated to check whether it’s true or false. It is “true” when then the scalar value is not the null string. Boolean doesn’t let any conversions to happen since it is a don’t-care context.
  • Void Context: This context neither cares for the type of the return value nor does it want a return value. It is no different from an ordinary scalar context from the standpoint of how functions work.
  • Interpolative Context: This context only happens inside a quote or things that act like a quote.
-w gives us the warnings about the possible interpretation errors in the script.

–t is used for switching on taint checking. It checks the origin of the variables where outside variables are not allowed in subshell executions and system calls.

Strict calls the strict pragma and is used to check on usage of variables, references. It is also used to force a check on the definition.

Perl language supports several operator types. The important ones are-
  • Arithmetic operators: These include addition(+), subtraction(-), multiplication(*), division(/), modulus(%), etc.
  • Equality operators also known as relational operators, these include == (equal to), != (not equal to), > (greater than), < (less than), etc.
  • Assignment operators These operators assign specific values and include =, +=, -+, *=, /=, etc.
  • Logical operators these include &&, or, ||, not, etc.
  • Quote-like operators In this, {} depicts any kind of delimiters. These include q{}, qq{}, qx{}, etc.
Subroutines accept an argument, perform the necessary operation and return the value. It is a named block of code, and often the term subroutine and function are used interchangeably. Subroutine takes the PROTOTYPE as the prototype of arguments and ATTRIBUTES as the attributes of the argument. Its syntax is: sub NAME or sub NAME PROTOTYPE ATTRIBUTES when the prototypes and attributes are optional.
Perl one-liners are one line command programs that are used for success of any operation. They may include more than one Perl statements, and one advantage to using it is that the program can be typed and executed from the command line instantly. Example:

The #run program, but with warnings

Perl –w my_file

The #run program under debugger

Perl –d my_file

Lists are special types of arrays that hold a series of values. The list can be explicitly generated by the user, or it can be a value returned by a function. Users can generate it using parenthesis and comma to separate the values.
If you want to store the result of any expression, then iValues are used. These are scalar values which are found on the left-side of the expression. It represents the data space in the memory.
  • Grooving and shortening of arrays: This can be done by giving a non-existent index to which Perl will automatically adjust the array size as needed.
  • Splicing of arrays: Instead of just extracting another array, splicing just copies and replaces elements from the array using the position specified in the splice function. Syntax: ARRAY, OFFSET, LENGTH, LIST.
  • Goto label: at this label, execution stops at the current point and resumes at the point where the label is specified. You cannot jump to a point inside a subroutine using Goto Label.
  • Goto name: it replaces the subroutine that is currently executing with a call to a particular subroutine instead. It automatically calls a different subroutine dynamically selects alternative routines.
  • Goto expr: it is an extension of Goto label.
  • Chomp: It removes the last character from the expression. It may remove each element of the list if it matches the value $/. It is considered to be safer than chop as it removes only when there is a match.
  • Chop- It removes last character and each element.
  • CPAN- Comprehensive Perl Archive Network(CPAN) is a large collection of Perl software.
Perl bit-wise operators work on bits and perform bit-by-bit operations. It includes-
  • AND(&) : this operator compares two bits and copies the bit to result if it exists in both operands.
  • OR(|) : it compares two bits and copies the bit if it exists in either of the operands.
  • XOR(^) : it copies the bit if it is there in on operand and not other.
  • ~ : this complement operator is uniary.
Ans. Local operator: this operator can operate on global variables.

My operator: this operator is used to define or create a new variable. Variables created by this operator are always private.

The closure is a block of code that is used to capture the environment where it is defined, and it captures lexical variables that the block consists of.
C has more development tools, and it also executes faster than Perl. In C, you don’t have to hide your code if you don’t want others to use them. However, in case of Perl, you have to hide your Perl code to prevent others from using them.
The interpreter compiles the Perl program internally into a parse tree. Any word after a profound symbol will be ignored. Once compiled, the interpreter will execute it immediately.