Perl's behavior isn't defined when you read the value of a variable and then auto-increment/decrement it later in the same statement. Try doing this instead and you'll get the behavior you expect:

$| = 0;

print "first=$|,";
$|--;
print "second=$|\n";

$| = 1;

print "first=$|,";
$|--;
print "second=$|\n";
[download]

In your first case, Perl evaluates the second $|, then decrements it, then evaluates the first one, leading to the unexpected behavior. The reason you don't end up with "-1" is that there is magic associated with $|. It doesn't actually hold a value, it just tracks whether it is set to a non-zero value or not. Try for instance  $| = -3; print $| to see this behavior.

Read perlvar and perlop for more information on what is going on here.

---

---

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.