Explain the use of the special variables $_ and @_ in Perl.?

In Perl, the special variable ‘$_‘ is called the default or implicit variable. It is used as a default argument or default operand value in a number of functions and operators.

Here are some examples:

1. ‘foreach‘ loop:

The ‘foreach‘ loop is used to iterate over elements in an array or a list. By default, ‘$_‘ is the variable that contains the current element in the array or list being processed.

my @nums = (1, 2, 3, 4, 5);

foreach (@nums) {
  print $_, "n"; # prints each number in the @nums array
}

Output:

1
2
3
4
5

2. ‘grep‘ function:

The ‘grep‘ function is used to filter out elements from an array or a list based on a condition. In this case, ‘$_‘ is used as the current element being processed.

my @nums = (1, 4, 6, 7, 9);

my @even_nums = grep { $_ % 2 == 0 } @nums; # filters even numbers from @nums array

print join(" ", @even_nums), "n"; # prints "4 6"

3. ‘s///‘ operator:

The ‘s///‘ operator is used for performing regular expression substitutions. In this case, ‘$_‘ is used as the default scalar variable that contains the string to be replaced.

my $string = "hello world";

$string =~ s/world/Perl Programming/; # replaces 'world' with 'Perl Programming'

print $string, "n"; # prints "hello Perl Programming"

The ‘@_‘ variable is another Perl special variable that is used to store the arguments passed to a subroutine. It is an array variable that stores the list of arguments passed, and can be accessed like any other array.

Here is an example:

sub add_numbers {
  my $total = 0;
  
  foreach my $num (@_) {
    $total += $num;
  }
  
  return $total;
}

my $result = add_numbers(4, 6, 8, 10); # pass a list of numbers as input

print $result, "n"; # prints "28"

In the above example, the ‘add_numbers‘ subroutine takes a list of numbers as input and calculates their sum by iterating over the elements in the ‘@_‘ array. Finally, it returns the total sum.