Perl | Implementing a Stack

Last Updated : 11 Jul, 2025

Stack in Perl is a linear data structure that follows the LIFO (Last In First Out) or FILO (First In Last Out) order.
In simpler terms, a stack is an array in which insertion and deletion takes place at only one end called the top of the stack.
Pushing is the process of insertion of elements into a stack.
Popping is the process of removal of topmost element of a stack.

Making a stack

Creating a stack in Perl is rather simple. All we need to do is declare an array.
The stack could be empty, as follows:

@stack;

Or it could be initialized:

@stack = (1, 2, 3);

Pushing items to a stack

Pushing can be done using either the push() function or the splice() function.

Pushing using push():

Syntax: push(@stack, list); Parameters:

@stack - The stack on which push is to be performed.

list - The elements to be pushed into a stack. These elements might be scalar, array, hash or any combination of these.

Example:

Perl

#!/usr/bin/perl

# Intitialising the Stack
@stack = (1..3);

# Original stack
print "Original Stack: @stack";

# Scalar to be pushed
$scalar = "scalar";

# Array to be pushed
@array = ("a", "r", "r", "a", "y");

# Hash to be pushed
%hash = ("Geeks" => 10, 
         "for Geeks" => 20);
         
# scalars, arrays and hashes can be
# inserted at the same time
push(@stack, ($scalar, @array, %hash)); 

# Updated Stack after 
# Push operations
print("\nUpdated Stack: @stack");

Output:

Original Stack: 1 2 3
Updated Stack: 1 2 3 scalar a r r a y Geeks 10 for Geeks 20

Pushing using splice():

Syntax: splice(@stack, scalar(@stack), 0, list); Parameters:

splice() function appends the 'list' at the end of @stack.

THe 'list' could be a scalar, an array or a hash.

Example:

perl

#!/usr/bin/perl

# Intitialising the Stack
@stack = (1..3);

# Original stack
print "Original Stack: @stack";

# Scalar to be pushed
$scalar = "scalar";

# Array to be pushed
@array = ("a", "r", "r", "a", "y");

# Hash to be pushed
%hash = ("Geeks" => 10, 
         "for Geeks" => 20);

# scalars, arrays and hashes can be
# inserted at the same time
splice(@stack, scalar(@stack), 0, 
       ($scalar, @array, %hash));
       
# Updated Stack after 
# Push operations
print("\nUpdated Stack: @stack");

Output:

Original Stack: 1 2 3
Updated Stack: 1 2 3 scalar a r r a y Geeks 10 for Geeks 20

Popping elements from a Stack

Popping can be done using either the pop() function or the splice() function.

Popping using pop():

Syntax: $popped_element = pop(@stack); Parameters:

pop() function returns the popped element.

$popped_element contains the element popped from the stack.

Example:

perl

#!/usr/bin/perl

# Intitialising the Stack
@stack = (1..3);

# Original stack
print "Original Stack: @stack";

# Topmost element i.e. 3 is 
# removed and returned
$popped_element = pop(@stack); 

# Printing popped element
print "\nPopped element: $popped_element";
       
# Updated Stack after 
# Pop operation
print("\nUpdated Stack: @stack");

Output:

Original Stack: 1 2 3
Popped element: 3
Updated Stack: 1 2

If the stack is empty, undef is returned. undef is analogous to NULL in Java and None in Python. However, no error is raised.

Example:

perl

#!/usr/bin/perl

# Creating a Stack
@stack;

# undef is returned since the 
# stack is empty. 
# No error is raised.
$popped_element = pop(@stack); 

# Printing popped element
# Since it contains no value,
# hence a blank space is returned
print "Popped element: $popped_element";

Output:

Popped element:

Popping using splice()::
Syntax: $popped_element=splice(@stack, -1); Parameters:
- splice() function removes the last element of the stack and returns it.
- $popped_element stores the returned value.
Example:
perl
#!/usr/bin/perl # Intitialising the Stack @stack = (1..3); # Original stack print "Original Stack: @stack"; # popping using splice() $popped_element = splice(@stack, -1); # Printing popped element print "\nPopped element: $popped_element"; # Updated Stack after # Pop operation print("\nUpdated Stack: @stack");
Output:
```
Original Stack: 1 2 3
Popped element: 3
Updated Stack: 1 2
```
- An error is raised, if the stack is empty. The following code raises an error: