/tmp>cat at.pl
#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;
use feature 'say';

say '@foo!';
say "\@bar!";
say "@bang!";

/tmp>perl at.pl
Possible unintended interpolation of @bang in string at at.pl line 10 (#1)
    (W ambiguous) You said something like '@foo' in a double-quoted string
    but there was no array @foo in scope at the time.  If you wanted a
    literal @foo, then write it as \@foo; otherwise find out what happened
    to the array you apparently lost track of.

Global symbol "@bang" requires explicit package name (did you forget to declare "my @bang"?) at at.pl line 10.
Execution of at.pl aborted due to compilation errors (#2)
    (F) You've said "use strict" or "use strict vars", which indicates
    that all variables must either be lexically scoped (using "my" or "state"),
    declared beforehand using "our", or explicitly qualified to say
    which package the global variable is in (using "::").

Uncaught exception from user code:
        Global symbol "@bang" requires explicit package name (did you forget to declare "my @bang"?) at at.pl line 10.
        Execution of at.pl aborted due to compilation errors.

/tmp>