foreach $symname (sort keys %main::) {
    local *sym = $main::{$symname};
    print "\$$symname is defined\n" if defined $sym;
    print "\@$symname is nonnull\n" if         @sym;
    print "\%$symname is nonnull\n" if         %sym;
}

##</code><code>##

hossman@slate:~/tmp/9780596004927/programming_perl_examples [master] $ perl -E "say $^V"
v5.26.1

##</code><code>##

hossman@slate:~/tmp/9780596004927/programming_perl_examples [master] $ perl ./program_listings/ch10/ch10.002.pl
 is defined
$ is defined
$" is defined
$/ is defined
$0 is defined
$@ is defined
%CORE:: is nonnull
%DynaLoader:: is nonnull
%ENV is nonnull
@INC is nonnull
%IO:: is nonnull
%Internals:: is nonnull
%PerlIO:: is nonnull
%Regexp:: is nonnull
%UNIVERSAL:: is nonnull
%constant:: is nonnull
%main:: is nonnull
%mro:: is nonnull
%re:: is nonnull
$symname is defined
%utf8:: is nonnull
%version:: is nonnull

##</code><code>##

hossman@slate:~/tmp/9780596004927/programming_perl_examples [master] $ perl -Mwarnings -Mstrict ./program_listings/ch10/ch10.002.pl
Variable "$sym" is not imported at ./program_listings/ch10/ch10.002.pl line 3.
Variable "@sym" is not imported at ./program_listings/ch10/ch10.002.pl line 4.
Variable "%sym" is not imported at ./program_listings/ch10/ch10.002.pl line 5.
Global symbol "$symname" requires explicit package name (did you forget to declare "my $symname"?) at ./program_listings/ch10/ch10.002.pl line 1.
Global symbol "$symname" requires explicit package name (did you forget to declare "my $symname"?) at ./program_listings/ch10/ch10.002.pl line 2.
Global symbol "$symname" requires explicit package name (did you forget to declare "my $symname"?) at ./program_listings/ch10/ch10.002.pl line 3.
Global symbol "$sym" requires explicit package name (did you forget to declare "my $sym"?) at ./program_listings/ch10/ch10.002.pl line 3.
Global symbol "$symname" requires explicit package name (did you forget to declare "my $symname"?) at ./program_listings/ch10/ch10.002.pl line 4.
Global symbol "@sym" requires explicit package name (did you forget to declare "my @sym"?) at ./program_listings/ch10/ch10.002.pl line 4.
Global symbol "$symname" requires explicit package name (did you forget to declare "my $symname"?) at ./program_listings/ch10/ch10.002.pl line 5.
Global symbol "%sym" requires explicit package name (did you forget to declare "my %sym"?) at ./program_listings/ch10/ch10.002.pl line 5.
Execution of ./program_listings/ch10/ch10.002.pl aborted due to compilation errors.