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Perl scripting


OO Perl

Perl & Databases

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© The scientific sentence. 2010


1. Introduction

Scalar variable allows us to store scalar wich is a number or a string. Array variable allows us to store a collection of scalars. We can access each scalar data in array by using indices. Hash variables (associative arrays before) allows us to store collective data type as an array does. Each element of a hash has two parts: key and value or key-value pair. We access an element of a hach by keys To define a hash variable, we use percentage sign (%) as follows: %hash = ("keys" => "values"); Example: -------- %books = ( "Physics" => "203", "Mathematics" => "305", "Chemistry"=> "407" );

2. Accessing un element of %hash

The sytax is: %hash {key}; print $books{"Mathematics"}; Outputs: 305 Remark: We can assign an hash to an array and vice versa. @hash = %hash; or %hash = @hash;

3. Adding Hash elements

To add hash elements, add a line as follows: %books = ( "Physics" => "203", "Mathematics" => "305", "Chemistry"=> "407" ); $books {"Geography"} = "509";

4. To test whether a key exists

To test whether a key exists in a hash, we use exist() function as folllow: if ( exists $hash{key} ){ # ... some code goes here .. } Example: if(exists $books{"Geography"}){ print "This discipline exists .."};

5. Removing keys from a Hash

To remove a key from a hash, we use delete function as follows: delete $hash{key}; To remove all keys and values from a hash, just assign hash to an empty list: %hash = ();

6. Looping through a Hash

The syntax is: foreach $element (keys %hash){ # ... some code goes here .. } Example: #!c:\www\Perl\bin %books = ( "Physics" => "203", "Mathematics" => "305", "Chemistry"=> "407" ); foreach $book (keys %books){ print "$book \n"; } foreach $book (values %books){ print "$book \n"; } outputs: C:\www\PERL> Chemistry Physics Mathematics 407 203 305

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