I don't have a script named "main".

main is the default package if no package statement has declared any other.

I have no idea what perl would think if I tried $main::DEBUG.

This is the "fully qualified" form of a package-global name. It is always valid. Even under strict, fully-qualified package globals can always be accessed with or without pre-declaration. Some examples: 

Win8 Strawberry 5.30.3.1 (64)  Mon 03/22/2021  6:33:58
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

package Bar {
    # package-globals can always be accessed in fully-qualified form
    $main::foo = "hi, i'm assigning this in " . __PACKAGE__ . "\n";
    }

print "A: this is being printed from default package ", __PACKAGE__, "
+\n";

# global $foo not yet declared in main: must access fully-qualified
print "B: i'm accessing this from ", __PACKAGE__, ": $main::foo";

our $foo;  # declare global $foo in package main
print "C: i'm accessing this from ", __PACKAGE__, ": $foo";

^Z
A: this is being printed from default package main
B: i'm accessing this from main: hi, i'm assigning this in Bar
C: i'm accessing this from main: hi, i'm assigning this in Bar

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Give a man a fish:  <%-{-{-{-<

In reply to Re^3: How to import "global" variables into sub-scripts from main script? by AnomalousMonk
in thread How to import "global" variables into sub-scripts from main script? by Polyglot

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