Perl Programming for Beginners

Perl is a high-level, interpreted, general-purpose programming language originally developed for text manipulation. It borrows many features from C and Shell script and is used for system administration, networking, and other applications that involve user interfaces. It was initially developed by Larry Wall in 1987 as a scripting language to make report processing easier and is implemented into the C programming language. Perl refers to the Perl5 version through 2019, when it was redesigned as sister language, Perl6, before it was altered to Raku in October 2019.

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Perl Features

The following list of features are available in Perl and are broadly adopted from other programming and scripting languages:

  • Perl gets most of its features from C, including variables, expressions, statements, control structures, and subroutines 
  • It also borrows features from shell scripting for identifying data types. unambiguously, like an array, scalar, hash, through leading sigils
  • Perl also has inbuilt functions which are often used in shell programming, such as sort and system facilities utilization
  • Perl5 also has added features to support complex data structures and an object-oriented programming model that includes packages, references, and directives for the compiler
  • All of the versions of Perl include auto data typing and memory management; the interpreter understands storage and memory requirements for each data type, allocates, and deallocates memory based on usage
  • It also does typecast during the run time like converting an integer to string etc. and other conversions, which are not legitimate, that are thrown out as errors during execution
  • Perl doesn’t enforce or recommend any particular programming technique like procedural, object-oriented, or functional—the interpreter, along with its functions, stands as a single specification of the language
  • Perl comes with powerful utilities (APIs) for text manipulation that are useful for working with XML, HTML, and other markup languages
  • Perl has the highest level of security and is even certified by a third-party security organization called Coverity, with low defect density and fewer security flaws
  • Perl is also extendable and provides libraries to support XML and integration to databases including Oracle and MySQL

Applications of Perl

Perl is popular among programmers, along with other programming languages like PHP and Python. In earlier days, programmers used Perl to write CGI scripts. Perl is often used as a departmental glue between multiple systems that are not homogenous or allowed to interoperate seamlessly. The system administers love this language as they can enter a single command to accomplish a goal that otherwise would require a program to be written. Perl is mainly portable, with some degree of customizations between Windows and macOS. 

Developers also use the language to build and deploy. It is used by most of the suppliers or software manufacturers to package and deploy the software commercially (including COTS and bespoke). It is widely used in the field of finance and bioinformatics due to its ability to handle and process large volume data sets.

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Perl Implementation

Perl is an interpreted language, as mentioned above, written in C with an extensive collection of modules written in both C and Perl. The Perl interpreter is a whopping 150,000 lines of C code, which compiles to 1 MB on most of the system architecture. There are more than 500 modules in Perl distribution with 300, 000 lines of code in Perl and 200,000 lines of code in C. The interpreter is based on the object-oriented architecture in which the elements of Perl (arrays, scalars, and hashes) are represented as C structures.

The interpreter passes through two phases in its life cycle compile and run phase. At compile time, the interpreter parses the Perl code into a syntax tree. At run time, it runs the Perl program by moving along the tree. Perl language is distributed as open source with 120,000 functional tests; it runs during the build process and extensively tests the interpreter and other functional modules. If your changes pass all of these 120K functional tests, you can safely assume that your code will not break the interpreter.

Variables and Types

Perl is a case-sensitive programming language like UNIX. Perl variables always start with $, @, or %, followed by zero, letters, or other digits, supporting three variable types (namely Scalars, Arrays, and Hashes). There are no Boolean data types in Perl, and assignment operation is carried out using = sign. # sign starts with the comment.

  • Scalars – These variables contain a single string or numeric value and the variable name should start with $

$item_name = “Orange”

  • Arrays – These variables are ordered sets of values and are prefixed with @

@item_name=(“Orange”, “Grape”, “Lemon”)

  • Hashes – these are key-value pairs, and they are prefixed with %

%item_catalog = ("Orange" => 5 , "Grape" => 8, "Lemon” => 24);

Decision Statements

Perl conditional statements allow statements to be executed based on true or false conditions. These conditional statements include:

  • if (condition) statement
  • if (condition) {statement1; statement2;}
  • if (condition) statement else statement

$x=1

$y=2

if ($x = 1) then {

print “x is less than y”

} else

print “y is greater than x”

  • The ternary operator ? which is also a conditional operator is used similarly as an alternative to the above statement.

(condition) ? statement1: statement2

  • if (condition) elsif (condition) statement else statement
  • unless (condition) statement
  • unless (condition) statement else statement
  • unless (condition) elsif (condition) statement else statement

Looping Statements

Like any other programming language, Perl also implements looping constructs through while and for statements. It executes the statements in the block repeatedly until the conditions are met. There are two types of while statements.

WHILE – DO WHILE

The below statement will check for the condition until it is true before executing the block:

$cnt = 5;

while ($cnt > 0) {

  print "Timer is: $cnt\n";

  $cnt--;

}

The below statement will check for the condition until it is false before executing the block:

$cnt = 1;

until ($cnt > 10) {

  print "Timer is: $cnt\n";

  $nt++;

}

The below block uses do while where the condition is tested or checked after executing the block:

$cnt = 5;

do {

print "Timer is: $cnt\n";

$cnt--;

} while ($cnt > 0)

FOR – FOR EACH

The following for loop statements are similar to C language statements where it initializes, checks the conditions, and iterates:

for ($cnt = 1 ; $cnt < 10 ; $cnt++) {

  print "My timer is: $cnt\n"; }

If you’re working on arrays, for each can be used to perform looping construct:

@cols = ('red', 'blue', ‘green');

foreach $cols (@cols) {

    print "Color: $cols\n";

}

Operator

The operator in Perl is an element that influences the operands in all of the Perl expressions, and it supports many operators like any other programming language. There are different types of operators in Perl, including:

  • Arithmetic operators (addition, subtraction, negation, multiplication, division, modulus, and exponent)
  • Assignment operators (assignment simple, subtract and assign, addition and assign, multiply and assign, divide and assign, increment and decrement, exponent and assign)
  • Bitwise operators (AND, OR, XOR, NOR, Shift Left and Shift Right)
  • Logical operators (Logical AND, Logical OR, Logical XOR, Logical NOT)
  • String operators (. for concatenation and x for repeating)
  • Misc operators (range operators for specifying the range)

Subroutine

Subroutines are critical to any programming language to enhance the modularity. They refer to the group or collection of statements collectively performing a task in a program, and they can be called from anywhere in the program, with or without arguments. The general syntax of the subroutine in Perl is given below:

sub name_of _subroutine {

body of the subroutine

}

name_of _subroutine (argument list);

For example:

sub Hi_Intro {

     print "Hi, this is my first subroutine\n";

}

The subroutine can be called in the following two ways (with and without ampersand)

Hi_Intro();

&Hi_Intro;

You can also pass arguments to the subroutines depending on the need of the program or the task it wants to accomplish.

Regular Expressions

The regular expression in Perl is an important feature as it is most helpful in the extraction and reporting of data (mostly text). The regular expression in Perl is used in numerous ways:

  • Search string that follows a specific pattern and replacing them with other string based on options
  • Counting the number of occurrences of a string or number in the line of text or numbers
  • Date formatting like converting date to mm/dd/yyyy from dd/mm/yyyy
  • Validation of fields submitted by the user in the front end typically in the HTML format

Why is Perl the Right Programming Tool for the Job?

Coding in the Perl program is always fun and enjoyable, as you do not have to worry about the memory allocation, complex syntax, or data structures. With limited effort, you can port your code across multiple operating systems. You can write compelling and shorter programs by mastering the Perl language through various utilities available, and it’s an entirely open source.

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