Unknown discipline ':utf8' w/ maint perl w/o perlio

[p5sagit/p5-mst-13.2.git] / pod / perlfaq6.pod

diff --git a/pod/perlfaq6.pod b/pod/perlfaq6.pod
index 9bbf80a..168233b 100644 (file)
--- a/pod/perlfaq6.pod
+++ b/pod/perlfaq6.pod
@@ -292,14 +292,26 @@ a double-quoted string (see L<perlop> for more details).  Remember
 also that any regex special characters will be acted on unless you
 precede the substitution with \Q.  Here's an example:
 
-    $string = "to die?";
-    $lhs = "die?";
-    $rhs = "sleep, no more";
+    $string = "Placido P. Octopus";
+    $regex  = "P.";
 
-    $string =~ s/\Q$lhs/$rhs/;
-    # $string is now "to sleep no more"
+    $string =~ s/$regex/Polyp/;
+    # $string is now "Polypacido P. Octopus"
 
-Without the \Q, the regex would also spuriously match "di".
+Because C<.> is special in regular expressions, and can match any
+single character, the regex C<P.> here has matched the <Pl> in the
+original string.
+
+To escape the special meaning of C<.>, we use C<\Q>:
+
+    $string = "Placido P. Octopus";
+    $regex  = "P.";
+
+    $string =~ s/\Q$regex/Polyp/;
+    # $string is now "Placido Polyp Octopus"
+
+The use of C<\Q> causes the <.> in the regex to be treated as a
+regular character, so that C<P.> matches a C<P> followed by a dot.
 
 =head2 What is C</o> really for?
 
@@ -667,15 +679,18 @@ guaranteed is slowness.)  See the book "Mastering Regular Expressions"
 hope to know on these matters (a full citation appears in
 L<perlfaq2>).
 
-=head2 What's wrong with using grep or map in a void context?
+=head2 What's wrong with using grep in a void context?
 
-The problem is that both grep and map build a return list,
-regardless of the context.  This means you're making Perl go
-to the trouble of building a list that you then just throw away.
-If the list is large, you waste both time and space.  If your
-intent is to iterate over the list then use a for loop for this
+The problem is that grep builds a return list, regardless of the context.
+This means you're making Perl go to the trouble of building a list that
+you then just throw away. If the list is large, you waste both time and space.
+If your intent is to iterate over the list, then use a for loop for this
 purpose.
 
+In perls older than 5.8.1, map suffers from this problem as well.
+But since 5.8.1, this has been fixed, and map is context aware - in void
+context, no lists are constructed.
+
 =head2 How can I match strings with multibyte characters?
 
 Starting from Perl 5.6 Perl has had some level of multibyte character