#!/usr/bin/perl
my $decimal=-33;
#How to generate:
#$decimal - your Perl variable. MUST be: -127<$decimal<127
my $packed=pack("N",$decimal); # Little-endian 4 byte.
my $YOUR8BITVALUE=substr($packed,-1); # last byte from $packed

open F,">your_test_file";
print F $YOUR8BITVALUE;
close F; 
#   Now you have file with your $decimal 
#   as one byte in "two's complement";


# How to get from file:
open F, "<your_test_file";
read(F,$packed,1); #read byte;
my $value; # result
if (unpack("N","\x00\x00\x00".$packed) & (1<<7)) { 
# sign bit is set. It's negative value
  $packed=("\xFF\xFF\xFF").$packed; # expand to int with 3 byte of 0xFF
  $value=-(unpack("N",~$packed)+1); # inverse all bits and unpack,increment,reverse sign.
} else {
  $packed=("\x00\x00\x00").$packed; # expand to int
  $value=unpack("N",$packed); unpack
}
print "$value\n"; # That's all!