# Usage: STRING = ReadFile(FILENAME, START, LENGTH)
# Reads an entire file or part of a file in binary mode.
# Returns the file contents as a string.
# An optional second argument will move the file pointer before reading,
# and an optional third argument limits the number of bytes to read.

sub ReadFile
{
   my $F = defined $_[0] ? $_[0] : '';
   $F =~ tr#><*%$?\r\n\"\0|##d;
   -e $F || return '';
   -f $F || return '';

   my $S = -s $F;
   $S || return '';

   my $L = defined $_2 ? $_2 : $S;
   $L > 0 || return '';

   local *H;
   sysopen(H, $F, 0) || return '';
   binmode H;
   my $P = defined $_1 ? $_1 : 0;
   $P >= 0 or $P = 0;
   $P < $S || return '';

   $P < 1 || sysseek(H, $P, 0);

   my $D = '';
   sysread(H, $D, $L);
   close H;
   return $D;
}