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.

  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: Perl

#!/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

    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: Perl

#!/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();         

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

#!/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;         

    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: Perl

#!/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"; 
} 

Here, nothing is printed as the stated Array is empty. So, the code does not displays the content of the if-statement. Program 2: Perl

#!/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"; 
} 

Here, the above stated Array is not empty so, the content of the if-statement is printed.     In order to place readline operator (i.e, <STDIN>) in Scalar Context it is required to designate this operator to a scalar variable. Example: Perl

#!/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.