The false positive does not show on my pc unless I use unpack('h*' $_); so I am sure it is a platform/architecture scenario between our PC's.

Not a platform mismatch, I would say, but probably because you're still reading a single character at a time from the file. If more than one character is read, the  /13/ ambiguity | false positive can appear with either  'H*' or  'h*' unpack templates:

c:\@Work\Perl>perl -wMstrict -le
"print 'A: found 0x13!' if  unpack('H*',        'a1') =~ /13/;
 print 'B: found 0x13!' if  unpack('h*', qq{\x{1f}s}) =~ /13/;
"
A: found 0x13!
B: found 0x13!
[download]

(BTW: The  * in both  'H*' and  'h*' implies reading and operating on a string of more than one character.)

I am not up to par on Unicode because ...

... and because you value your sanity.

Update: Another, perhaps more general, code example:

c:\@Work\Perl>perl -wMstrict -le
"use Data::Dump qw(pp);
 ;;
 for my $s ('a1', qq{\x{1f}s}) {
   print q{'H*' found 0x13! in }, pp($s) if unpack('H*', $s) =~ /13/;
   print q{'h*' found 0x13! in }, pp($s) if unpack('h*', $s) =~ /13/;
   }
"
'H*' found 0x13! in "a1"
'h*' found 0x13! in "a1"
'h*' found 0x13! in "\37s"
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.