Thanks for posting. I have two minor suggestions, if you are interested at all.

sub GetFile2
...
sub isAbsPath
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If you don't want your users/co-developers to pull their hair out and curse your name into the void for eternity, don't arbitrarily capitalise the first letter of your sub names. Pick a format (any format) and stick to it.

sub isAbsPath
{
  @_ or return 0;
  my $P = shift;
  defined $P or return 0;
  length($P) or return 0;
  $P = uc(substr(Trim($P), 0, 3));
  my $c = vec($P, 0, 8);
  return 1 if ($c == 47 || $c == 92);
  return 0 if ($c < 65 || $c > 90);
  return 0 if (vec($P, 1, 8) != 58);
  $c = vec($P, 2, 8);
  return 1 if ($c == 47 || $c == 92);
  return 0;
}
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Did you know that perl has regular expressions? That will save all this hard-coding of ord values, etc. eg:

sub isAbsPath {
    my $path = shift;
    return 0 unless defined $path;
    return $path =~ /^([A-Z]:|[\/\\])/ ? 1 : 0;
}
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You could omit the ternary if you're only interested in a true/false return value. I've only demonstrated this one subroutine but many others could benefit from such simplification.

The alternative is to use a module. For this case, eg is_absolute from Path::Tiny.

The more you code in Perl, the more Perlish your code will become. Enjoy the journey.