Perl Subroutines

Subroutines are sections of code that can take arguments, perform some operations with them, and may return a meaningful value.

 Subroutines help our programming for two main reasons. 
  • First, They let us reuse code, This makes it easier for us to write programs. 
  • The second reason is that they allow us to chunk our code into organizational sections.
1) Defining a subroutine and call it 
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# Function definition
sub demo{
 print "This is Subroutine.\n";
} 
# Function Call
demo;
Output: This is Subroutine.

 2) Passing an argument to Subroutine. Parameters are accessed inside a subroutine using special array @_ i.e it holds all arguments passed. Hence, the arguments will start with $_[0], $_[1], $_[2], $_[3] and so on.
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# Function definition
sub addition{
 # get total number of arguments passed.
 $num = scalar(@_);
 $sum = 0;
 
 foreach $item (@_) {
  $sum = $sum + $item;
 }
 
 print "Sum of the given numbers : $sum\n";
} 
# Function Call
addition(5,10);
Output: Sum of the given numbers : 15

 Example of accessing the parameters in subroutine
Single Parameter:
$x = shift;    #Shift operator removes and return the first value
$x = $_[0];  #first argument to the function is in $_[0]

 Multiple parameters:
$x = $-[1];   # the second parameter is in $_[1]
my ($p1, $p2) = @_;   #if there are two arguments
foreach $item (@_)      # For each loop to access all elements
my @list = @_             # Collecting all elements in list
my (%hash) = @_;      # Collecting all elements in hash

 3) Return value by subroutine 
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# Function definition
sub addition{
 # get total number of arguments passed.
 $num = scalar(@_);
 $sum = 0;
 
 foreach $item (@_) {
  $sum = $sum + $item;
 }
 
 return $sum;
} 
# Function Call
$result = addition(5,10);
print $result
Output: 15

 4) Passing arrays and hashes to Subroutine. 
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@fruits = ('apple', 'orange', 'banana');
%data = ('Jerry' => 32, 'Adam' => 31, 'Chris' => 22);

# Function Call
printArrayElements(@fruits);
printHashElements(%data);

# Function definition
sub printArrayElements{
 my @list = @_;
 print "Given list is @list\n";
}

sub printHashElements{
 my %hash = @_;
 foreach my $key ( keys %hash ) {
  my $value = $hash{$key};
  print "$key : $value\n";
 }
}

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