Perl | Scalar Context Sensitivity

Introduction:
In Perl, function calls, terms, and statements have inconsistent explications which rely upon its Context. There are two crucial Contexts in Perl, namely List Context and Scalar Context. In a list context, Perl gives the list of elements. But in a scalar context, it returns the number of elements in the array. When an operator functions on Scalars then its termed as Scalar Context.
Note:

• Whenever you assign anything to a Scalar variable it will always give Scalar Context.
• In this Context, presumption is to obtain a single value.
• An array if assigned to Scalar variable will return its size.

Creating a Scalar Context

Scalar Context can be generated with the use of Scalar variables, Numerical operator, and many more.

• Assignment to a Scalar variable:
  Example:

  $x = @z;

  $x = localtime();

  $x = Scalar;

  Here, localtime() displays time in human readable format whereas in List Context this function shows number depiction of time.

• Assignment to a single element of an array:
  Example:
  
  

  $a[2] = Scalar;

  Every element of an array is individually a Scalar. So, assignment to them generates Scalar Context.

• Numerical operators creating Scalar Context:
  Example:

  3 + Scalar;

  Scalar + 3;

  A numerical operator can generate Scalar Context on either sides of it.

• Concatenation creating Scalar Context:
  Example:

  "GFG" . Scalar;

  Scalar . "GFG"

  From the above example, it is clear that Concatenation can generate Scalar Context on both side of itself.

Example:

#!/usr/bin/perl
# Perl program of creating Scalar Context

# array of elements
my @CS = ('geeks', 'for', 'geeks', 'articles');

# Assignment to a Scalar variable
my $x = @CS;

# Assignment of a function
# to a Scalar variable
# Note: Time displayed here
# will be the GMT
my $y = localtime();

# Numerical operator creating
# Scalar Context
my $z = 3 + @CS;

# Displays number of elements
# in an Array
print "$x\n";

# Displays time stored in array
# in human readable format
print "$y\n";

# Displays sum of a number
# and Scalar
print "$z\n";

# Concatenation creating
# Scalar Context
print "The number of elements are: " . @CS

Output:

4
Wed Mar 27 07:01:56 2019
7
The number of elements are: 4

Forcing Scalar Context

One must require to force Scalar Context when Perl presumes a List. So, in that case you can utilize scalar() function which generates Scalar Context as Perl is informed by this function to impart Scalar Context for its parameters.
Example:

#!/usr/bin/perl
# Perl program of Forcing Scalar Context

# array of elements
my @x = ('geeks', 'for', 'geeks');

# Forcing Scalar context to display
# number of elements in an Array
print scalar @x;
print "\n";

# Displaying time in human readable
# format by forcing Scalar Context
print scalar localtime();

Output:

3
Sun Mar 17 06:12:53 2019

Arrays in Scalar Context

In order to provoke Scalar Context using an array, it is required to assign an array to a Scalar variable.
Example:

#!/usr/bin/perl
# Perl program of Arrays in Scalar Context

# array of elements
my @x = ('geeks', 'for', 'geeks');

# Assignment of an Array to
# a Scalar variable
my $y =  @x;

# Displays number of elements in
# an Array
print $y;

Output:

3

Use of if-statement in Scalar Context

When the condition section of the if-statement presumes a single value then that is Scalar Context. In the below program, if-statement contains array, in scalar context, array returns the number of elements in it. So, if the array is empty then it will return 0 hence, if-statement will not execute if the array passed to it as scalar context is empty.
Program 1:

#!/usr/bin/perl

# Program of if-statement in Scalar Context
use strict;
use warnings;
use 5.010;

# Array with no elements
my @w = ();

# Statement within 'if' will be executed
# only if the array is not empty
if (@w)
{
    print "Geeks";
}

Output:

No Output

Here, nothing is printed as the stated Array is empty. So, the code does not displays the content of the if-statement.

Program 2:

#!/usr/bin/perl

# Program of if-statement in Scalar Context
use strict;
use warnings;
use 5.010;

# An Array of elements
my @w = ('G', 'f', 'G');

# Statement within 'if' will be executed
# only if the array is not empty
if (@w)
{
    print "There are some elements in the Array";
}

Output:

There are some elements in the Array

Here, the above stated Array is not empty so, the content of the if-statement is printed.

Reading in SCALAR Context

In order to place readline operator (i.e, <STDIN>) in Scalar Context it is required to designate this operator to a scalar variable.
Example:

#!/usr/bin/perl
# Program to Read input from user
use strict;
use 5.010;

# Asking the user to provide input
print "Enter your name:\n";

# Getting input from user
my $y = <STDIN>;

# Printing the required output
print "My name is $y\n";

Output:

Above program accepts the input from the user with the use of <STDIN> and store it in the Scalar variable. Further, use that scalar variable to print the Input provided by the user.