sysseek($fh,0,0) returned "0 but true"
sysseek($fh,42,0) returned 42
sysseek($fh,-1,0) returned undef

        undef: bool=false, str=          "", num=0 (warns: uninit x 2)
           "": bool=false, str=          "", num=0 (warns: numeric)
            0: bool=false, str=         "0", num=0
          "0": bool=false, str=         "0", num=0
            1: bool=true , str=         "1", num=1
          "1": bool=true , str=         "1", num=1
        "foo": bool=true , str=       "foo", num=0 (warns: numeric)
  Perl's true: bool=true , str=         "1", num=1
 Perl's false: bool=false, str=          "", num=0
 "0 but true": bool=true , str="0 but true", num=0
 "3 and true": bool=true , str="3 and true", num=3 (warns: numeric)
        "0E0": bool=true , str=       "0E0", num=0
          0E0: bool=false, str=         "0", num=0
          1E0: bool=true , str=         "1", num=1
        "1E0": bool=true , str=       "1E0", num=1

##</code><code>##

use warnings;
use strict;
use File::Temp qw/tempfile/;
use Data::Dumper;
sub pp { Data::Dumper->new([@_])->Useqq(1)->Terse(1)
	->Indent(0)->Dump }

my ($fh) = tempfile(UNLINK=>1);
print $fh "Perl"x12;
for my $pos (0, 42, -1) {
	my $rv = sysseek($fh,$pos,0);
	print "sysseek(\$fh,$pos,0) returned ",pp($rv),"\n";
}
print "\n";

my @vals = (
	'undef'        => undef,         # warns as number and string
	'""'           => "",            # warns as number
	'0'            => 0,
	'"0"'          => "0",
	'1'            => 1,
	'"1"'          => "1",
	'"foo"'        => "foo",         # warns as number
	"Perl's true"  => !0,
	"Perl's false" => !1,
	'"0 but true"' => "0 but true",  # doesn't warn as number (!)
	'"3 and true"' => "3 and true",  # warns as number
	'"0E0"'        => "0E0",
	'0E0'          => 0E0,
	'1E0'          => 1E0,
	'"1E0"'        => "1E0",
);
while (@vals) {
	my ($desc, $val) = (shift @vals, shift @vals);
	#no warnings qw/ uninitialized numeric /;
	printf "%13s: bool=%-5s, str=%12s, num=%s%s\n", do {
		my %w;
		local $SIG{__WARN__} = sub {
				my $w = shift;
				if ($w=~/numeric/)
					{ $w{numeric}++ }
				elsif ($w=~/uninitialized/)
					{ $w{uninit}++ }
				else { warn $w }
			};
		($desc, $val?'true':'false', '"'.$val.'"', 0+$val, keys(%w)
			? " (warns: ".join(',',map {$w{$_}>1?"$_ x $w{$_}":$_}
			sort keys %w).")" : '' );
	};
}