What is use of ‘strict’ in perl ?
The module strict restricts ‘unsafe constructs’, according to the perldocs
When you enable the strict module, the three things that Perl becomes strict about are:
• Variables ‘vars’
• References ‘refs’
• Subroutines ‘subs’
Strict variables are useful. Essentially, this means that all variables must be declared, that is defined before use. Furthermore, each variable must be defined with my or fully qualified

What is scalars in perl ?
The most basic kind of variable in Perl is the scalar variable. Scalar variables hold both strings and numbers, and are remarkable in that strings and numbers are completely interchangable. For example, the statement
$priority = 9;
sets the scalar variable $priority to 9, but you can also assign a string to exactly the same variable:
$priority = ‘high’

Perl difference between lists and arrays ?
A list is a fixed collection of scalars. An array is a variable that holds a variable collection of scalars.
Array operations, which change the scalars, reaaranges them, or adds or subtracts some scalars, only work on arrays. These can’t work on a list, which is fixed. Array operations include shift, unshift, push, pop, and splice.
You can change an array element, but you can’t change a list element.

What is the use of ‘defined’?
defined EXPR
defined

Returns true if EXPR has a value other than the undef value, or checks the value of $_ if EXPR is not specified.
If EXPR is a function or function reference, then it returns true if the function has been defined.

Return Value
• 0 if EXPR contains undef
• 1 if EXPR contains a valid value or reference

#!/usr/bin/perl
$var1 = "This is defined";
if( defined($var1) ){
  print "$var1\n";
}
if( defined($var2) ){
  print "var2 is also defined\n";
}else{
  print "var2 is not defined\n";
}
This will produce following result
This is defined
var2 is not defined