Perl Interview Questions and Answers

Practical extraction and reporting language (PERL) is an open-source software that is used to develop web-based applications even though libraries are available to perform web server applications and networking components. The features of PERL programming are:

• PERL works with other markup languages like HTML, XML, etc.
• It enjoys the best features from languages such as C, awk, sh, sed, etc.
• The third-party databases like Oracle, Postgres, MySQL, etc. are all supported by the PERL database integration interface.
• PERL is a Y2K complaint that supports Unicode.
• PERL is quite flexible and easily readable.

• PERL is known as the duct tape of the internet.
• PERL can accelerate the processing by up to 2000% when embedded into the web servers.
• Due to the rapid development cycle and text manipulation features, PERL is one of the most popular web programming languages.
• PERL can handle encrypted web data and e-commerce transactions. The popular e-commerce site Amazon is built on PERL.
• Due to its simple syntax, PERL is very easy to comprehend.
• All versions of PERL do automatic data-typing and dynamically allocate memories to programmes and free it for use when not needed.

PERL has three basic data types. They are:

• Scalar data type: These are simple variables that are either a number, string or a reference. Scalar data types start with a dollar sign($). Scalar values are by default undefined. A scalar value is interpreted as TRUE in the Boolean sense if it not a null string.
• Arrays of scalar: These are the ordered list of scalars that can be accessed by a numeric index and starts with a 0. They start with "at" sign (@). In simpler words, array stores the list of scalar values.
• Hashes of scalars: Hashes are also known as associative arrays and are preceded by a percentage sign (%). Hashes are unordered sets of value pairs that can be accessed using the keys as subscripts. It stores associative arrays that use a key-value as an index instead of numerical indexes. It is a third major data type after scalars and arrays.

• -w : this argument highlights the warning.
• -c : this only helps in the compilation and not run.
• -d : it is used for debugging.
• -e : this argument helps in execution.
• -wd: it is a combination derived from –w and –d. we can use other combinations as well.
• -a : it automatically splits the group of input files.
• -T : it switches on the taint mode.
• -d:module : in this argument, the script is compiled and the control is transferred to the specified module.

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.

• 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 the 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.

The #run program, but with warnings

Perl –w my_file

The #run program under debugger

Perl –d my_file

• 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.

• 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.

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

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.