Question

I am using use strict; in perl and with that I use the following statement.

unless(defined($x)){
      print "Not defined";
}

Where $x is not declared anywhere. So I expect it to print “Not defined” but it returns an error

Global symbol "$x" requires explicit package name at *********** in line 15.

Answer 1

The strict pragma has three parts: strict references, strict variables, and strict subs. The one you’re running into is

strict vars

This generates a compile-time error if you access a variable that wasn’t declared via our or use vars, localized via my, or wasn’t fully qualified. Because this is to avoid variable suicide problems and subtle dynamic scoping issues, a merely local variable isn’t good enough.

Because it generates compile-time errors, your non-BEGIN code won’t even have a chance to run. You can temporarily allow non-strict variables inside a block as in

{
  no strict 'vars';
  print "Not defined!\n" unless defined $x;
}

but note that Perl’s defined operator tells you whether a value is defined, not whether a variable has been declared.

Tell us more about your application, and we can give you better advice about how to handle it.