PERL

Introduction to Perl

Perl (Practical Extraction & Reporting Language) is widely used open-source language. It was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular amongst programmers. Larry Wall continues to work on development of the core language, and its upcoming version, Perl 6. Perl borrows features from other programming languages including C, shell scripting (sh), AWK, and sed. The language provides powerful text processing facilities, facilitating easy manipulation of text files. Perl gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its parsing abilities.

Perl can be used as a very simple and easy to use programming language. This language helps programmer to write a simple piece of code against the heavy / complicated shell or C programming. This language is portable and reliable. Useful for applications requiring Pattern Matching extensively

Basic Level

Installation of Perl

1. Installation of Perl 5.14.2 on Ubuntu Linux
   • Installing XAMPP in Linux

   (XAMPP is a cumulative package consisting of Apache, PERL, PHP and MySQL Packages is available for Linux)

   • Default Webserver directory will be set to "opt"

   OR

   • Using default Perl installation available in Synaptic Package Manager
2. Installation of Perl 5.14.2 on Windows
   • Installing XAMPP in Windows

   (XAMPP is a cumulative package consisting of Apache, PERL, PHP and MySQL Packages is available for Windows)

   • Default Webserver directory will be set to "htdocs"

   
   

   Topics

3. Variables in Perl
   • Variables are used for storing values, like text strings, numbers or arrays
   • All variables in PERL start with a $ sign symbol
   • Declaring a variable in PERL: $var_name = value;
   • e.g:
     • $count = 1;
     • $stringVar = ‘My Name is PERL’;
4. Comments in Perl
   • Two types of comments -
     • Single Line
     • Multi Line
   • Single Line comment starts with the symbol #
   • Multi Line comment used to comment a chunk of code
     • =cut =head or =begin =end
     • Start with = sign

   
   

   Loops in Perl

5. for-foreach-Loop
   • for Loop
     • for loop is used to execute a piece of code for certain number of times
     • Syntax:
       for (initialization;condition;increment)
       {
       Piece of code to be executed multiple times
       }
     • eg:
       for ($i=0; $i<=4; $i++)
       {
       print “Value of i: $i\n”;
       }
   • for-each Loop
     • for-each loop is used to iterate a condition over an array
     • Syntax:
       foreach $variable (@array)
       {
       Perform action on each element of array
       }
     • eg:
       @myarray = (10, 20, 30);
       foreach $var (@myarray)
       {
       print “Element of array is: $var \n”;
       }
6. while-do-while Loops
   • while Loop
     • while loop executes a block of code while a condition is true.
     • Syntax:
       while (condition)
       {
       Piece of code to be executed only while the condition is true
       }
     • eg:
       $i = 0;
       while ($i<=4)
       {
       print “Value of i: $i\n”;
       $i++;
       }
   • do-while Loop
     • do-while loop will always execute the piece of code at-least once
     • It will then check the condition and repeat the loop while the condition is true
     • Syntax:
       do
       {
       Piece of code to be executed while the condition is true
       }do (while);
     • eg:
       $i = 0;
       do
       {
       print “Value of i: $i\n”;
       $i++;
       }while ($i<=4);

   
   

   Conditional Statements

7. if-if-else Statements
   • if Statement
     • if statement is used to execute piece of code only if a specified condition is satisfied.
     • Syntax:
       if (condition)
       {
       Piece of code to be executed;
       }
     • eg:
   • if-else Statement
     • if-else statement is used to execute piece of code if a condition is satisfied or another code if the condition is false.
     • Syntax:
       if (condition)
       {
       Piece of code to be executed;
       }else {
       Another piece of code;if the above if condition evaluates to false, this another piece of code will be executed
       }
     • eg:
8. if-elsif-else-switch Statements
   • if-elsif-else Statement
     • if-elsif-else statement is used to select one of several blocks of code to be executed.
     • Syntax:
       if (condition)
       {
       Piece of code to be executed;
       }elsif (other condition) {
       Another piece of code;if the above if condition evaluates to false, this another piece of code will be executed
       }else{
       #piece of code to be executed if both the above conditions are false.
       }
     • eg:
   • switch Statement
     • switch statement is used to select one of many blocks of code to be executed.
     • There were no Switch/Case in perl prior to 5.8 version.
     • After 5.8 PERL provided Switch module.
     • Syntax:
       use switch;
       $variable;
       switch ($variable){
       case(1) { ....}
       case(2) { ....}
       case(3) { ....}
       else { ....}
       }
     • eg:
       use switch;
       $var = 2;
       switch ($var){
       case(1) { $i = “One”}
       case(2) { $i = “Two”}
       case(3) { $i = “Three”}
       else { $i = “Other”}
       }
       $i will become 2
9. Data Structures in Perl
   • Scalar
     • These are the basic variables in PERL.
     • It can hold any kind of type viz. string, number etc.
     • eg: $variable = 9;
       $variable = ‘This is string type of variable’;
   • Array
     • Array in PERL is ordered collection of data.
     • It can hold data of any type.
     • Array index starts from zero.
     • eg: @array = (1, 5, 6, ‘abc’, 7);
   • Associative Array or Hash
     • Associative array or Hash in PERL is un-ordered collection of data.
     • It is a key value pair.
     • Key cannot be duplicate in hash whereas value can be.
     • eg:
       %hash = (
       ‘Name’ => ‘John’,
       ‘Department’ => ‘Finance’
       );
10. More on Arrays
    • Getting Last index of array
      • eg:
        @array = (1, 5, 6, ‘abc’, 7);
        print “Last index of an array is: $#array”;
        # prints… Last index of an array is: 4
    • Getting length of an array
      • To get the length, add 1 to last index of an array
      • eg: print “Length of an array is: ”, $#array+1;
        # prints.. Length of an array is: 5
      • Other way is use scalar function on array or assign array to a scalar variable.
      • eg:
        scalar (@array);
        $length = @array;
    • Accessing element of an array
      • eg:
        @array = (1, 5, 6, ‘abc’, 7);
        # print the 4th element of an arrayprint $array[3];
      • prints…. “abc”
    • Looping over an array
      • There are two ways to loop over an array
        • Using for loop
        • eg:
          @array = (1, 5, 6, ‘abc’, 7);
          for ($i=0; $i<$#array; $i++) {
          print $array[$i];
          }
        • Using for-each loop
        • eg:
          @array = (1, 5, 6, ‘abc’, 7);
          foreach $var (@array) {
          print $var;
          }
11. Basic array functions
    • push
      • Add element at the end of an array
    • pop
      • Remove element from the end of an array
    • unshift
      • Add element at the start of an array
    • shift
      • Remove element of an array from the start.
    • split
      • This function splits the string and makes an array of it.
      • eg:
        $var = ‘Hello World’
        @array = split (/ /, $var);
        $var will get split on space and @array will contain 2 elements Hello World
    • qw
      • qw stands for “Quoted word”
      • It returns a list of word separated by white spaces.
      • eg:
        @array = qw (Hello world) this is equivalent to @array = (‘Hello’, ‘World’);
    • sort
      • sorts the array in alphabatical order.
12. More on Hash
    • Accessing element of a hash
      • Syntax:
        %hash = (
        ‘Name’ => ‘John’,
        ‘Department’ => ‘Finance’
        );
        print $hash{Name};
        #prints… John
    • Basic hash functions
      • keys
        • Returns keys of a hash
      • values
        • Returns values of a hash
      • each
        • Retrieve the next key/value pair from a hash
    • Looping over a hash
      • Syntax:
        foreach ($key = (keys %hash)) {
        print $hash{$key};
        }
        OR
        foreach (($key, $value) = each (%hash)) {
        print “Key: $key & value: $value”;
        }
13. Functions in Perl
    • Simple function
      • Syntax:
        sub sample_func {
        #piece of code
        }
    • Function with parameters
      • Syntax:
        sub func_with_parameters {
        ($variable) = @_;
        # @_ contains the arguments passed to function.
        #This is a special PERL variable.
        }
    • Function which return single value
      • Syntax:
        sub return_single_value {
        #piece of code
        
        
        return $variable;
        }
    • Function which returns multiple values
      • Syntax:
        sub return_multiple_value {
        #piece of code
        return ($variable1, $variable2);
        }
14. Blocks in Perl
    • Begin
      • This block executes at the compilation time once it is defined.
      • Anything which needs to be included before execution of the rest of the code is written here.
      • Syntax:
        begin {
        #piece of code to be executed at the start
        }
    • End
      • This block executes at the end.
      • Anything which needs to be executed at last is written here.
      • Syntax:
        end {
        #piece of code to be executed at the end
        }

Intermediate level

Topics

1. Access Modifiers in PERL
   • my
     • this is kind of private variable.
     • scope is in the block inside where it is declared.
   • local
     • this kind of variables are lexically scoped variables
     • that means they get the temporary value inside the block where it is used
     • as soon as block ends it gets the earlier value.
     • ie, 'local' temporarily changes the value of the variable, but only within the scope it exists.
   • our
     • this is kind of global variables in perl
     • can be accessed without giving package name while accessing it in another package.
     • e.g:
       package first;
       our $varInFirst = 10;
       package second;
       print $varInFirst; # prints 10
2. Referencing & Dereferencing in Perl
   • Referencing
     • In perl we can create a reference by adding \ (backward slash) to it.
     • eg:
       $variable = 10;
       $variableRef = \$variable;
       @array = (1, 2 , 3);
       $arrayRef = \@array;
       %hash = (
       ‘Emp Id’ => 1000,
       ‘Name’ => ‘Peter’
       );
       $hashRef = \%hash;
     • Note: Reference in perl is nothing but a perl scalar variable holding address of the entity being referred.
   • De-referencing
     • Dereferencing is the mean by which we can get the actual entity being referred by reference.
     • It is done by putting appropriate identifier in front of the reference variable.
     • eg:
       $scalar = $$scalarRef;
       @array = @$arrayRef;
       %hash = %$hashRef;
3. Special Variables in PERL
   • These variables in perl have some special meaning.
4. Sample Perl Programs
5. Exception and error handling in PERL
   • eval block in perl
     • User can use eval, if he wants to execute a piece of code even if there is a error / exception
     • or to know exactly where the code is failing with the type of error.
     • eg:
       eval {
       my $var = 10;
       my $result = $var / 0;
       };
       
       if ($@) {
       die “Error: $!”;
       # This will terminate the execution of the program.
       If user wants to ignore this and just want to know the error use print instead of die.
       }
6. File Handling
   • To open a file
     • open FH, FileName.txt; # FH is the file handle
   • To open a file in read mode
     • open FH, "<FileName.txt";
   • To open a file in read, write mode
     • open FH, ">FileName.txt";
   • To open a file in append mode
     • open FH, ">>FileName.txt";
   • Looping on each line can be done as
     • eg:
       while (<FH>) {
       print "$_"; # prints each line of a file
       }
   • write into a file
     • print FH "I am writing in a file";
   • close the file handle
     • close FH
7. Including files and/or modules in a PERL program
   • do
     • it includes a file without checking that the file is already included or not
   • require
     • it includes a file if it not included already.
   • use
     • it includes perl module files only.
     • Files get included before the actual execution of the code gets start.
8. Perl Modules
   • These are the .pm files.
   • Modules can be used to reuse piece of code written earlier by someone and serves the user requirement.
   • e.g:When we write
     use DBI;
     This gives me access to the functions already written to connect to DB and for querying DB.
9. PERL Module library
   • CPAN
     • Comprehensive Perl Archive Network is the library for modules.
     • We can search for require module in CPAN.
     • If user is wrting his own module and wants to make it available to other Perl users also, he needs to upload it on CPAN.
10. Adding path to a default list of paths for a module
    • @INC
      • If user has downloaded a module on a path of his choice and
      • wants to include this module into a perl program he needs to add that module into @INC array. #** This needs to be done at the start of program and can be achieved by using begin block;
      • begin {
        unshift (@INC,"user/choice/path/of/file");
        };
11. Downloading required module onto windows or linux
    • Downloading CPAN module
      • Windows
        • With installation of PERL on windows, a utility called PPM (Perl Package Module) gets installed.
        • This utility can be used to search and install the require module on windows environment.
        • This also installs dependencies if any.
      • Linux: There are several ways on linux;
        • type cpan and enter.
          • This gives us cpan prompt.
          • Type install ModuleName and it will install the module.
        • perl -MCPAN -e 'install ModuleName';
12. PERL & HTML
    • CGI module
      • To create html pages, perl provides CGI module
      • It creates CGI script with require html tags:
      • There are different methods which CGI modules provide to
        • add header,
        • adding fields to the page,
        • retrieving the values of the parameters posted on to the form.

Advanced level

Topics

1. Function Prototyping
2. Date & Time
   • Current Time Stamp
   • Various Date formats
   • Various operations that can be performed on date
3. Oops in Perl
   • Object creation
   • Constructor
   • Destructor
   • Accessing methods using an object
   • Inheritance in Per
4. Exporting functions in Perl
   • EXPORT
   • EXPORT_OK
5. Pattern Matching / Regular expression in Perl
   • Basics of pattern matching
   • Syntax
   • Modifiers
6. Database handling
   • DBI module
7. Multithreading
   • threads module
8. Socket Programming
   • use IO::Socket::INET
9. General information
   • Getting Perl version
   • Perl installation path
   • Information about the
     • module
     • it’s location
     • from where it is included in your perl script

Contributors and Content Editors

AmolBrahmankar, Nancyvarkey, Nirmala Venkat, PoojaMoolya