perl -V:ptrsize

##</code><code>##

perl -E"use Config qw( %Config ); say $Config{ptrsize};"

##</code><code>##

use Config qw( %Config );

my $ptr_size = $Config{ptrsize};
my $ptr_format =
   $ptr_size == 8 ? 'Q' :
   $ptr_size == 4 ? 'L' :
   die("Unrecognized pointer size");

my $s = unpack 'p', pack $ptr_format, $addr;

##</code><code>##

>perl -wE"say unpack 'p', pack('P', 'abc')"
abc

>perl -wE"say unpack 'p', pack('P', 'abc').qq{\0\0\0\0\0\0\0\0}"
abc

##</code><code>##

my $s = unpack 'p', pack 'J', $addr;

##</code><code>##

# works(??): 'my potato'
my $x = unpack 'p', pack 'N2', $return;
print Dumper $x;

##</code><code>##

>perl -wE"say sprintf '%vX', pack 'J', 0x0000000012345678"
78.56.34.12.0.0.0.0

##</code><code>##

>perl -wE"say sprintf '%vX', pack 'N2', 0x0000000012345678"
12.34.56.78.0.0.0.0

##</code><code>##

# works(??): 'my potato'
my $x = unpack 'p', pack 'IN', $return;
print Dumper $x;

##</code><code>##

>perl -wE"say sprintf '%vX', pack 'J', 42952784"
50.68.8F.2.0.0.0.0

>perl -wE"say sprintf '%vX', pack 'IN', 42952784"
50.68.8F.2.0.0.0.0

##</code><code>##

>perl -wE"say sprintf '%vX', pack 'J', 0x0123456789ABCDEF"
EF.CD.AB.89.67.45.23.1

>perl -wE"say sprintf '%vX', pack 'IN', 0x0123456789ABCDEF"
EF.CD.AB.89.0.0.0.0