Errata

This is most disappointing. The webpage pointed to by this page where one is supposed to be able to download the book's examples from reults in a 2009 (?) link (the 2nd edition was published in 2003) to archived files contain examples having nothing to do with the book!

The file reference numbers (e.g. 01-01.plx) have examples that are not even close to the sections they should represent from the book (the one mentioned here is not even relevent to Section 1.1's example code).

Please fix this link (it's acutally in your "Examples" link under the left side of the web book description).

Please, I have many O'Relly books (both paper nad electronic editions) but this sort of qulaity makes me wonder what's going on back there these days.

Marty

http://oreilly.com/catalog/9780596003135/
http://examples.oreilly.com/9780596003135/

The first statement is :
printf "char %s is code %d, %#04x
", $char, $code, $code;

the supposed output (given previous assignments) is
char [capital delta] is code 916, 0x394

Using 5.8.4, I get the character ['I' with an arch over it]

The second statement is:
print "xC4 and x{0394} look different
";

The supposed output is:
char ['A' with an umlaut over it] and [capital delta] look different

I get:
Wide character in print at ...
['A' with '~' over it] and ['I' with an arch over it] look different

On my system:
mike@/deb40a:~> uname -a
Linux playground 2.4.27 #1 Mon Dec 24 13:55:08 PST 2007 i586 GNU/Linux

In sub getwinsize
# my $TIOCGWINSZ = 0x40087468; # from 'Perl Cookbook' sets $cols = 80
my $TIOCGWINSZ = 0x00005413; # from man ioctl_list, gives 25x80

The supplied glob2pat function does not convert ranges like [0-9] correctly, they get converted to [0\-9]. See also http://www.perlmonks.com/?node_id=708493.

A simplistic fix is:

sub glob2pat {
my $globstr = shift;
my %patmap = (
'*' => '.*',
'?' => '.',
'[' => '[',
']' => ']',
'-' => '-', # Added by Clive
'\\' => '\\', # also added by Clive
);

$globstr =~ s{(.)} { $patmap{$1} || "\Q$1" }ge;

return '^' . $globstr . '$';
}

However, this still does not cope with escaped characters like \?, \[, or \*, or these characters inside [] which should not be converted. They get converted regardless.

The "may overlap" regular expression: /^(?=.*ALPHA)BETA/s
is incorrect. The "^" should not be present.

"True if both /ALPHA/ and /BETA/ match, but may overlap ..."

The RE listed requires that BETA be at the beginning of the string (and even without "^", it has
to be before ALPHA)

A correct RE is:
/(?:(?=.*ALPHA)BETA)|(?:(?=.*BETA)ALPHA)/s

@lines = shuffle(@lines);
NOWREADS
@reordered = shuffle(@lines);

The fourth line in the assigement to @dirs is:
map {[$_, "$path/$_"]}

The value of $path is never set.

return unless -f && -s _ > $saved_size;
$saved_size = -s _;

should be:

return unless -f && -s $_ > $saved_size;
$saved_size = -s $_;

$age = (stat(_))[9];

should be:

$age = (stat($_))[9];

The last sentence in the first paragraph of the Discussion, "For more fine-grained control,
Stat::lsMode offers format_mode ..." describes how file_mode is stated to work in the previous
sentence.

The next paragraph confuses the issue further. "The format_perms function ... " is not in the
following example. The example shows file_mode working as it did in the first Discussion
paragraph, but format_mode returns a 9-character string, which is what format_perms was supposed
to do.

addition to previous submission:

The last sentence in the first Discussion paragraph states that format_mode takes a numeric
permissions value. That now seems to be OK, but the Solution is supposed to convert numeric
permissions, yet file_mode is called with $pathname as an argument.

The whole Solution and Discussion need to be rewritten.

The example includes:
case (@array) ...
case (%hash) ...

The lines ought to be

case [@array] ...
case [%hash] ...

I believe that insert_value is incorrect since it weakens all references to the newly
created node, exposing it to garbage
collection as soon as &insert_value returns. Clearly, at least one reference to
$node must stay strong. Since $node is not returned from $insert_value, its caller
cannot maintain the strong reference.

I believe it would be better to have for example all PREV references weak and all
NEXT references strong with the exception of the last one, i.e., $ring->{PREV}-
>{NEXT} which should be weak (to break the circle).

This state of affairs can be maintained by not calling weaken on $node->{NEXT} nor on
$ring->{NEXT} in &insert_value, by not calling weaken on $node->{PREV}->{NEXT} in
&delete_node and by continuing to call weaken on both $node->{NEXT} and $node->{PREV}
in &node.

line 68 is (page 495 - sub modname):
if (index($_, $Start_Dir . "/") = = 0) {
But should be:
if (index($_, $Start_Dir . "/") == 0) {

Also, I thought that the line 73 adds some extra spaces.

line 73 is (page 495 - sub modname):
s { .p(m|od)$ } { }x;
But was replaced by:
s { .p(m|od)$ } {}x;

lines 139-141 (page 497 - end of program):
format = ^<<<<<<<<<<<<<<<<<~~^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$Module, $_
.
But write command in page 496 (sub wanted, inside while) is commented, so I commented
lines 139-141:
#format =
^<<<<<<<<<<<<<<<<<~~^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
#$Module, $_
#.

After this correction, the following error is eliminated:
syntax error at ./pmdesc.pl line 139, near "format ="
Execution of ./pmdesc.pl aborted due to compilation errors.

The code at the bottom of the page doesn't work as of 12/10, most likely because the CPANPLUS module was altered since the printing of the book. Here's a version that works:

#!/usr/bin/perl -X
use CPANPLUS::Backend;
use CPANPLUS::Module;

$cp = CPANPLUS::Backend->new;
@installed = $cp->installed; # fetch list of installed mods

foreach my $module(sort {$a->name cmp $b->name} @installed)
{
# get the module's information
$details = $module->details;

# display the fields we care about
printf("%-35.35s %44.44s\n", $module->name, $details->{Description});
}

The following line of code is incomplete:

return sprintf("STR%s: %.*f", ref($self),
defined($self->{PLACES}) ? $self->{PLACES} : $PLACES,


It should have an extra argument to sprintf:

return sprintf("STR%s: %.*f", ref($self),
defined($self->{PLACES}) ? $self->{PLACES} : $PLACES, $self->{VALUE});

The code calls "param" and "url", but since the snipped includes no "use" statemtents, it's not possible to know where these subroutines come from. The "start" parameter is read near the bottom of page 574, but there is no code that reads it. The entire example needs to be redone.

In Section "17.6 Using UNIX Domain Sockets", the example code uses LocalAddr and PeerAddr, when it should be Local and Peer (the stupid IO::Socket module doesn't complain, but also doesn't work if you pass in the wrong parameter).

now:
$SIG{ALRM} = sub { close(FIFO) }; # move on to the next queued process

should be:
$SIG{ALRM} = sub { close($fifo) }; # move on to the next queued process

to be consistent with the rest of the program. The global filehandle
FIFO isn't used anywhere else.

The listed code first correctly masks off SIGINT:

sigprocmask(SIG_BLOCK, $sigset, $old_sigset)

However, to unblock, it suggests:

sigprocmask(SIG_UNBLOCK, $old_sigset)

This won't work. If $old_sigset was empty (because nothing was blocked initially), then unblocking the empty set won't change anything.

Either:

sigprocmask(SIG_UNBLOCK, $sigset)

Or:

sigprocmask(SIG_SETMASK, $old_sigset)

I'd prefer the SIG_UNBLOCK to undo a previous SIG_BLOCK (and SIG_SETMASK to restore after a previous SIG_SETMASK).

Text currently reads:

Fork once, and let the parent exit
$pid=fork;
exit if $pid; #ERROR HERE
$die "Couldn't fork: $!" unless defined($pid);

The line marked ERROR HERE should instead be

exit if $pid==0

or equivalent (such as "exit unless $pid"). This is because we want to run a daemon as the child and have the parent exit not the child. In its current form in the text both the parent and child processes will die or exit, leaving nothing around to do any work. In the corrected version the parent correctly exits and the child is left to do work if defined.

The call to format_string() has no argument that holds the string to be converted to ASCII.