Change 15237 by jhi@alpha on 2002/03/15 15:18:46
Be more explicit on when is the $! worth anything.
Affected files ...
.... //depot/perl/pod/perlvar.pod#89 edit
Differences ...
==== //depot/perl/pod/perlvar.pod#89 (text) ====
Index: perl/pod/perlvar.pod
--- perl/pod/perlvar.pod.~1~ Fri Mar 15 08:30:05 2002
+++ perl/pod/perlvar.pod Fri Mar 15 08:30:05 2002
@@ -673,9 +673,25 @@
=item $!
If used numerically, yields the current value of the C C<errno>
-variable, with all the usual caveats. (This means that you shouldn't
-depend on the value of C<$!> to be anything in particular unless
-you've gotten a specific error return indicating a system error.)
+variable, or in other words, if a system or library call fails, it
+sets this variable. This means that the value of C<$!> is meaningful
+only I<immediately> after a B<failure>:
+
+ if (open(FH, $filename)) {
+ # Here $! is meaningless.
+ ...
+ } else {
+ # ONLY here is $! meaningful.
+ ...
+ # Already here $! might be meaningless.
+ }
+ # Since here we might have either success or failure,
+ # here $! is meaningless.
+
+In the above I<meaningless> stands for anything: zero, non-zero,
+C<undef>. A successful system or library call does B<not> set
+the variable to zero.
+
If used an a string, yields the corresponding system error string.
You can assign a number to C<$!> to set I<errno> if, for instance,
you want C<"$!"> to return the string for error I<n>, or you want
End of Patch.
