use strict;

##</code><code>##

(SOME_ERROR_TEXT) at (FILE) line (LINE).
Execution of (FILE) aborted due to compilation errors.

##</code><code>##

# Code:
    $x  = 5;                            # no strict 'vars'
    print "$x\n";

# Output:
Global symbol "$x" requires explicit package name at strict-demo.pl line 10.
Global symbol "$x" requires explicit package name at strict-demo.pl line 11.
Execution of strict-demo.pl aborted due to compilation errors.

##</code><code>##

    my $x;                              # declare first
    $x  = 5;                            # strict okay
    print "$x\n";

##</code><code>##

    $newPig    = 'Keisha';

    # much, much later...
    print $Newpig;                      # prints nothing; why?

##</code><code>##

# Code:
    my $subroutine  = factorial;        # no strict 'subs'
    print $subroutine->(7), "\n";

# Output:
Bareword "factorial" not allowed while "strict subs" in use at strict-demo.pl line 13.
Execution of strict-demo.pl aborted due to compilation errors.

##</code><code>##

    my $subroutine  = \&factorial;      # strict okay
    print $subroutine->(7), "\n";

##</code><code>##

# Code:
    our $dog;
    my $pet     = 'dog';
    ${ $pet }   = 'Rover';              # no strict 'refs'
    print "$dog\n";

# Output:
Can't use string ("dog") as a SCALAR ref while "strict refs" in use at strict-demo.pl line 18.

##</code><code>##

    our $dog;
    my $pet     = \$dog;                # hard reference
    ${ $pet }   = 'Rover';              # strict okay
    print "$dog\n";

##</code><code>##

no strict 'vars';
no strict 'subs';
no strict 'refs';

##</code><code>##

#       strict-demo.pl
#       =  Copyright 2011 Xiong Changnian <xiong@cpan.org>   =
#       = Free Software = Artistic License 2.0 = NO WARRANTY =

use strict;             # comment out to avoid errors

#----------------------------------------------------------------------------#
# Uncomment lines to force strict errors...

#    $x  = 5;                            # no strict 'vars'
#    print "$x\n";

#    my $subroutine  = factorial;        # no strict 'subs'
#    print $subroutine->(7), "\n";

#    our $dog;
#    my $pet     = 'dog';
#    ${ $pet }   = 'Rover';              # no strict 'refs'
#    print "$dog\n";

#----------------------------------------------------------------------------#
# Uncomment this whole section for a successful run...

#    my $x;                              # declare first
#    $x  = 5;                            # strict okay
#    print "$x\n";

#    my $subroutine  = \&factorial;      # strict okay
#    print $subroutine->(7), "\n";

#    our $dog;
#    my $pet     = \$dog;                # hard reference
#    ${ $pet }   = 'Rover';              # strict okay
#    print "$dog\n";

#----------------------------------------------------------------------------#

print "Done.\n";

sub factorial {
    my $in      = shift;
    my $out     = 1;

    for my $factor (2..$in) {
        $out        *= $factor;
    };

    return $out;
};

__END__