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A Perl reference is a scalar data type that holds the location of another value which could be scalar, arrays, or hashes. Because of its scalar nature, a reference can be used anywhere, a scalar can be used.It is easy to create a reference for any variable, subroutine or value by prefixing it with a backslash as follows −$scalarref = \$foo; $arrayref = \@ARGV; $hashref = \%ENV; $coderef = \&handler; $globref = \*foo;You cannot create a reference on an I/O handle (filehandle or dirhandle) using the backslash operator but a reference to an anonymous array can be created using the ... Read More
The context of a Perl subroutine or statement is defined as the type of return value that is expected. This allows you to use a single function that returns different values based on what the user is expecting to receive. For example, the following localtime() returns a string when it is called in scalar context, but it returns a list when it is called in list context.my $datestring = localtime( time );In this example, the value of $timestr is now a string made up of the current date and time, for example, Thu Nov 30 15:21:33 2000. Conversely −($sec, $min, ... Read More
There is another type of lexical variable in Perl, which is similar to private variables but they maintain their state and they do not get reinitialized upon multiple calls of the subroutines. These variables are defined using the state operator and available starting from Perl 5.9.4.ExampleLet's check the following example to demonstrate the use of state variables − Live Demo#!/usr/bin/perl use feature 'state'; sub PrintCount { state $count = 0; # initial value print "Value of counter is $count"; $count++; } for (1..5) { PrintCount(); }OutputWhen the above program is executed, it produces the following result −Value ... Read More
The local is mostly used when the current value of a variable must be visible to called subroutines in Perl. A Perl local just gives temporary values to global (meaning package) variables. This is known as dynamic scoping. Lexical scoping is done with my, which works more like C's auto declarationsIf more than one variable or expression is given to local, they must be placed in parentheses. This operator works by saving the current values of those variables in its argument list on a hidden stack and restoring them upon exiting the block, subroutine, or eval.ExampleLet's check the following example ... Read More
By default, all variables in Perl are global variables, which means they can be accessed from anywhere in the program. But you can create private variables called lexical variables at any time with the my operator.The my operator confines a variable to a particular region of code in which it can be used and accessed. Outside that region, this variable cannot be used or accessed. This region is called its scope. Lexical scope is usually a block of code with a set of braces around it, such as those defining the body of the subroutine or those marking the code ... Read More
You can return a value from Perl subroutine as you do in any other programming language. If you are not returning a value from a subroutine then whatever calculation is last performed in a subroutine is automatically also the return value.You can return arrays and hashes from the subroutine like any scalar but returning more than one array or hash normally causes them to lose their separate identities. So we will use references ( explained in the next chapter ) to return an array or hash from a function.ExampleLet's try the following example, which takes a list of numbers and ... Read More
When you supply a hash to a Perl subroutine or operator that accepts a list, then the hash is automatically translated into a list of key/value pairs. For example −Example Live Demo#!/usr/bin/perl # Function definition sub PrintHash { my (%hash) = @_; foreach my $key ( keys %hash ) { my $value = $hash{$key}; print "$key : $value"; } } %hash = ('name' => 'Tom', 'age' => 19); # Function call with hash parameter PrintHash(%hash);OutputWhen the above program is executed, it produces the following result −name : Tom age : 19
Because the @_ variable is an array in Perl, it can be used to supply lists to a subroutine. However, because of the way in which Perl accepts and parses lists and arrays, it can be difficult to extract the individual elements from @_. If you have to pass a list along with other scalar arguments, then make list as the last argument as shown below −Example Live Demo#!/usr/bin/perl # Function definition sub PrintList { my @list = @_; print "Given list is @list"; } $a = 10; @b = (1, 2, 3, 4); # Function call with list ... Read More
You can pass various arguments to a Perl subroutine like you do in any other programming language and they can be accessed inside the function using the special array @_. Thus the first argument to the function is in $_[0], the second is in $_[1], and so on.You can pass arrays and hashes as arguments like any scalar but passing more than one array or hash normally causes them to lose their separate identities. So we will use references ( explained in the next chapter ) to pass an array or hash.Let's try the following example, which takes a list ... Read More
The general form of a subroutine definition in Perl programming language is as follows −sub subroutine_name { body of the subroutine }The typical way of calling that Perl subroutine is as follows −subroutine_name( list of arguments );In versions of Perl before 5.0, the syntax for calling subroutines was slightly different as shown below. This still works in the newest versions of Perl, but it is not recommended since it bypasses the subroutine prototypes.&subroutine_name( list of arguments );Let's have a look into the following example, which defines a simple function and then call it. Because Perl compiles your program before ... Read More
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