FAQ jumbo patch from tchrist.

Message-Id: <199901080605.XAA20229@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq.pod
Date: Thu, 7 Jan 1999 23:05:02 -0700

Message-Id: <199901080605.XAA20231@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq1.pod
Date: Thu, 7 Jan 1999 23:05:02 -0700

Message-Id: <199901080605.XAA20233@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq2.pod
Date: Thu, 7 Jan 1999 23:05:02 -0700

Message-Id: <199901080605.XAA20235@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq3.pod
Date: Thu, 7 Jan 1999 23:05:02 -0700

Message-Id: <199901080605.XAA20237@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq4.pod
Date: Thu, 7 Jan 1999 23:05:02 -0700

Message-Id: <199901080605.XAA20239@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq5.pod
Date: Thu, 7 Jan 1999 23:05:02 -0700

Message-Id: <199901080605.XAA20241@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq6.pod
Date: Thu, 7 Jan 1999 23:05:02 -0700

Message-Id: <199901080605.XAA20243@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq7.pod
Date: Thu, 7 Jan 1999 23:05:03 -0700

Message-Id: <199901080605.XAA20245@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq8.pod
Date: Thu, 7 Jan 1999 23:05:03 -0700

Message-Id: <199901080605.XAA20257@jhereg.perl.com>
From: Tom Christiansen <tchrist@jhereg.perl.com>
To: pumpkings@jhereg.perl.com
Subject: newest version of perlfaq9.pod
Date: Thu, 7 Jan 1999 23:05:03 -0700

p4raw-id: //depot/cfgperl@2588

1 files changed, 67 insertions, 60 deletions

diff --git a/pod/perlfaq6.pod b/pod/perlfaq6.pod
index 488a27c83a..834fd89aa1 100644
--- a/pod/perlfaq6.pod
+++ b/pod/perlfaq6.pod
@@ -1,6 +1,6 @@
 =head1 NAME
 
-perlfaq6 - Regexps ($Revision: 1.22 $, $Date: 1998/07/16 14:01:07 $)
+perlfaq6 - Regexps ($Revision: 1.25 $, $Date: 1999/01/08 04:50:47 $)
 
 =head1 DESCRIPTION
 
@@ -128,7 +128,7 @@ L<perlop>):
 
 If you wanted text and not lines, you would use
 
-    perl -0777 -pe 'print "$1\n" while /START(.*?)END/gs' file1 file2 ...
+    perl -0777 -ne 'print "$1\n" while /START(.*?)END/gs' file1 file2 ...
 
 But if you want nested occurrences of C<START> through C<END>, you'll
 run up against the problem described in the question in this section
@@ -387,48 +387,31 @@ See the module String::Approx available from CPAN.
 
 =head2 How do I efficiently match many regular expressions at once?
 
-The following is super-inefficient:
+The following is extremely inefficient:
 
-    while (<FH>) {
-        foreach $pat (@patterns) {
-            if ( /$pat/ ) {
-                # do something
-            }
-        }
-    }
-
-Instead, you either need to use one of the experimental Regexp extension
-modules from CPAN (which might well be overkill for your purposes),
-or else put together something like this, inspired from a routine
-in Jeffrey Friedl's book:
-
-    sub _bm_build {
-        my $condition = shift;
-        my @regexp = @_;  # this MUST not be local(); need my()
-        my $expr = join $condition => map { "m/\$regexp[$_]/o" } (0..$#regexp);
-        my $match_func = eval "sub { $expr }";
-        die if $@;  # propagate $@; this shouldn't happen!
-        return $match_func;
-    }
-
-    sub bm_and { _bm_build('&&', @_) }
-    sub bm_or  { _bm_build('||', @_) }
-
-    $f1 = bm_and qw{
-            xterm
-            (?i)window
-    };
-
-    $f2 = bm_or qw{
-            \b[Ff]ree\b
-            \bBSD\B
-            (?i)sys(tem)?\s*[V5]\b
-    };
-
-    # feed me /etc/termcap, prolly
-    while ( <> ) {
-        print "1: $_" if &$f1;
-        print "2: $_" if &$f2;
+    # slow but obvious way
+    @popstates = qw(CO ON MI WI MN);
+    while (defined($line = <>)) {
+	for $state (@popstates) {
+	    if ($line =~ /\b$state\b/i) {  
+		print $line;
+		last;
+	    }
+	}
+    }                                        
+
+That's because Perl has to recompile all those patterns for each of
+the lines of the file.  As of the 5.005 release, there's a much better
+approach, one which makes use of the new C<qr//> operator:
+
+    # use spiffy new qr// operator, with /i flag even
+    use 5.005;
+    @popstates = qw(CO ON MI WI MN);
+    @poppats   = map { qr/\b$_\b/i } @popstates;
+    while (defined($line = <>)) {
+	for $patobj (@poppats) {
+	    print $line if $line =~ /$patobj/;
+	}
     }
 
 =head2 Why don't word-boundary searches with C<\b> work for me?
@@ -460,22 +443,24 @@ not "this" or "island".
 
 =head2 Why does using $&, $`, or $' slow my program down?
 
-Because once Perl sees that you need one of these variables anywhere
-in the program, it has to provide them on each and every pattern
-match.  The same mechanism that handles these provides for the use of
-$1, $2, etc., so you pay the same price for each regexp that contains
-capturing parentheses. But if you never use $&, etc., in your script,
-then regexps I<without> capturing parentheses won't be penalized. So
-avoid $&, $', and $` if you can, but if you can't (and some algorithms
-really appreciate them), once you've used them once, use them at will,
-because you've already paid the price.
+Because once Perl sees that you need one of these variables anywhere in
+the program, it has to provide them on each and every pattern match.
+The same mechanism that handles these provides for the use of $1, $2,
+etc., so you pay the same price for each regexp that contains capturing
+parentheses. But if you never use $&, etc., in your script, then regexps
+I<without> capturing parentheses won't be penalized. So avoid $&, $',
+and $` if you can, but if you can't, once you've used them at all, use
+them at will because you've already paid the price.  Remember that some
+algorithms really appreciate them.  As of the 5.005 release.  the $&
+variable is no longer "expensive" the way the other two are.
 
 =head2 What good is C<\G> in a regular expression?
 
 The notation C<\G> is used in a match or substitution in conjunction the
 C</g> modifier (and ignored if there's no C</g>) to anchor the regular
 expression to the point just past where the last match occurred, i.e. the
-pos() point.
+pos() point.  A failed match resets the position of C<\G> unless the
+C</c> modifier is in effect.
 
 For example, suppose you had a line of text quoted in standard mail
 and Usenet notation, (that is, with leading C<E<gt>> characters), and
@@ -596,20 +581,41 @@ Or like this:
 
 Or like this:
 
-   die "sorry, Perl doesn't (yet) have Martian support )-:\n";
-
-In addition, a sample program which converts half-width to full-width
-katakana (in Shift-JIS or EUC encoding) is available from CPAN as
-
-=for Tom make it so
+    die "sorry, Perl doesn't (yet) have Martian support )-:\n";
 
 There are many double- (and multi-) byte encodings commonly used these
 days.  Some versions of these have 1-, 2-, 3-, and 4-byte characters,
 all mixed.
 
+=head2 How do I match a pattern that is supplied by the user?
+
+Well, if it's really a pattern, then just use
+
+    chomp($pattern = <STDIN>);
+    if ($line =~ /$pattern/) { }
+
+Or, since you have no guarantee that your user entered
+a valid regular expression, trap the exception this way:
+
+    if (eval { $line =~ /$pattern/ }) { }
+
+But if all you really want to search for a string, not a pattern,
+then you should either use the index() function, which is made for
+string searching, or if you can't be disabused of using a pattern
+match on a non-pattern, then be sure to use C<\Q>...C<\E>, documented
+in L<perlre>.
+
+    $pattern = <STDIN>;
+
+    open (FILE, $input) or die "Couldn't open input $input: $!; aborting";
+    while (<FILE>) {
+	print if /\Q$pattern\E/;
+    }
+    close FILE;
+
 =head1 AUTHOR AND COPYRIGHT
 
-Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington.
+Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
 All rights reserved.
 
 When included as part of the Standard Version of Perl, or as part of
@@ -624,3 +630,4 @@ are hereby placed into the public domain.  You are permitted and
 encouraged to use this code in your own programs for fun
 or for profit as you see fit.  A simple comment in the code giving
 credit would be courteous but is not required.
+