Syntax:
The syntax of declaring the Perl subroutine is shown in the following. The name of the subroutine is defined after the “sub” keyword:
The Perl subroutine can be called in different ways which are mentioned in the following:
- SubroutineName();
- &SubroutineName;
Perl Subroutine Examples
Declaring and calling the Perl subroutines for different purposes are shown in this part of the tutorial.
Example 1: Define the Subroutine without an Argument
Create a Perl file with the following script that declares a subroutine to print the value of a global variable by concatenating it with the value of a local variable. The “$str” variable is declared globally in the script. The “$text” variable is declared locally inside the subroutine.
use strict;
use warnings;
#Declare a string variable
my $str = "Perl Programming";
#Define the subroutine without any parameter
sub display_message {
my $text = "Learn ";
print "$text$str\n";
}
print "Output:\n";
#Call the subroutine
display_message();
Output:
The following output appears after executing the script:
Example 2: Define the Subroutine with an Argument
Create a Perl file with the following script that declares a subroutine to read a number that is taken from the user as an argument value and find out whether the number is even or odd. After taking the input from the user, the chomp() function is used to remove the new line from the input value. Next, the check_num() function is called with the argument and the “shift” function is used inside the function to read the argument value. The return statement is used in the function to return the message to the function caller.
use strict;
use warnings;
print "Enter a number: ";
#Take input from the user
my $num = <>;
#Remove newline
chomp($num);
#Call the function with one argument
print check_num($num);
#Define the function
sub check_num{
#Read the first argument value
my $n = shift;
#Check if the number is even or odd
if($n % 2 == 0)
{
return "$n is even number.\n";
}
return "$n is odd number.\n";
}
Output:
The following output appears after executing the script with the input value of 78:
The following output appears after executing the script with the input value of 55:
Example 3: Return the Value from the Subroutine Implicitly
The Perl subroutine can return the value without using a return statement and this type of return is called “implicit return”. In this example, two numeric values are taken from the user and passed to the subroutine named calculate_average(). This subroutine reads the argument values using @_ with a “for” loop and return the average value of the arguments through the “$avg” variable.
use strict;
use warnings;
#Take two numbers from the user and remove the newline
print "Enter the first number: ";
my $num1 = <>;
chomp($num1);
print "Enter the second number: ";
my $num2 = <>;
chomp($num2);
#Call the function with two arguments
print "The average of $num1 and $num2 is ".calculate_average($num1, $num2)."\n";
#Define the function
sub calculate_average{
my $sum = 0;
my $counter = 0;
#Read all arguments using loop
for my $v (@_){
$sum += $v;
$counter++;
}
#Count the average value
my $avg = $sum/$counter;
#Return average value
$avg;
}
Output:
The following output appears after executing the script with the argument values of 60 and 40:
Example 4: Pass an Array as an Argument Value in the Subroutine
In this example, an array of six numbers is declared and passed as the argument in the subroutine named sum_of_array_values(). The argument value is stored in an array using @_ inside the subroutine. Next, the sum of this array values is calculated by a “for” loop and is printed.
use strict;
use warnings;
use Data::Dumper;
#Declare an array as a number
my @num_arr = (10, 7, 45, 23, 90, 45);
print "The array values:\n";
#Print the array values
print Dumper(\@num_arr);
#Declare the function that will calculate the sum of array values
sub sum_of_array_values{
#Read the array from the argument
my @arr = @_;
my $sum = 0;
#Calculate the sum of array values
for(my $i = 0; $i <= $#arr; $i++)
{
$sum += $arr[$i];
}
print "The sum of array values is $sum\n";
}
#Call the function with an array as an argument
sum_of_array_values(@num_arr);
Output:
The following output appears after executing the script:
Conclusion
The methods of using the Perl subroutines for different purposes are explained in this tutorial using multiple Perl scripts.
