[25990] in Perl-Users-Digest
Perl-Users Digest, Issue: 8209 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Jun 28 06:05:21 2005
Date: Tue, 28 Jun 2005 03:05:05 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Tue, 28 Jun 2005 Volume: 10 Number: 8209
Today's topics:
Re: Checking IP addresses against lists of IPs, partial <tintin@invalid.invalid>
Re: Checking IP addresses against lists of IPs, partial <joe@inwap.com>
Re: perl script <tim@vegeta.ath.cx>
Re: perl script <joe@inwap.com>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@augustmail.com
Re: Simple Structure Question <tassilo.von.parseval@rwth-aachen.de>
Re: Simple Structure Question <tassilo.von.parseval@rwth-aachen.de>
Re: Simple Structure Question <joe@inwap.com>
Re: Typeglob Qs <pilkowsk@informatik.uni-marburg.de>
Re: Typeglob Qs <sisyphus1@nomail.afraid.org>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 28 Jun 2005 20:27:50 +1200
From: "Tintin" <tintin@invalid.invalid>
Subject: Re: Checking IP addresses against lists of IPs, partial IPs, and netmasks.
Message-Id: <%k8we.10922$U4.1402538@news.xtra.co.nz>
"Adam Funk" <a24061@yahoo.com> wrote in message
news:d9ok0j$2gdc$1@godfrey.mcc.ac.uk...
> I'm trying to write some Perl code to check an IP addresses against a list
> of strings containing IP address, partial IP addresses ending in ".",
> net/mask pairs and net/masklength pairs.
>
> In other words, I'd like ip_found("192.168.2.3") to return true if the
> test
> list contains any of the following:
> 192.168.2.3
> 192.168.
> 192.168.2.0/255.255.255.0
> 192.168.2.0/24
>
> I'm sure someone else has done this already -- any good code to recycle?
Have a look at:
http://search.cpan.org/~marcel/Net-IP-Match-0.01/Match.pm
http://search.cpan.org/~luismunoz/NetAddr-IP-3.24/IP.pm
------------------------------
Date: Tue, 28 Jun 2005 02:30:00 -0700
From: Joe Smith <joe@inwap.com>
Subject: Re: Checking IP addresses against lists of IPs, partial IPs, and netmasks.
Message-Id: <s8WdnSmZAYQLhVzfRVn-pQ@comcast.com>
axel@white-eagle.invalid.uk wrote:
>>192.168.2.3
>>192.168.
>>192.168.2.0/255.255.255.0
>>192.168.2.0/24
>
> However I suspect you are wanting to do more than that and check
> if the IP address is within a certain range... but then you would
> need to supply more information about the address to be checked
> (i.e. what class of address).
I've seen that syntax before. The class of address _is_ being provided.
192.168. = 192.168.*.* = 192.168.0.0:255.255.0.0 = 192.168/16
192.168.2 = 192.168.2.* = 192.168.2.0:255.255.255.0 = 192.168.2/24
192.168.2.0/24 = 192.168.2/24
192.168.2.3 = 192.168.2.3:255.255.255.255 = 192.168.2.3/32
-Joe
------------------------------
Date: Tue, 28 Jun 2005 04:51:43 GMT
From: Tim Hammerquist <tim@vegeta.ath.cx>
Subject: Re: perl script
Message-Id: <slrndc1lmh.9ll.tim@vegeta.saiyix>
yo <> wrote:
[ snip ]
> #!/usr/bin/perl
This should be the path to the perl executable on your system. The
above is usually fine, but to take advantage of the shell's shebang
functionality, the script needs to have execute permissions for the user
running it. These are unix issues; not perl.
Also, you probably meant:
#!/usr/bin/perl
use strict;
use warnings;
> open(INFILE, "@ARGV[0]");
You probably meant:
open(INFILE, $ARGV[0]) or die "can't open $ARGV[0]";
> $infile = <INFILE>;
> ($username,$password) = split(/\|/, $infile);
> close(INFILE);
>
> @calladduser = ("/usr/sbin/adduser -g 100 -d /home/sites/home/
> $password -s /sbin/nologin $username","\n");
> system("@calladduser");
You're calling system() incorrectly. system() may be called with either
1 argument, or multiple, the semantics of which are causing your
problem. see `perldoc -f system` (It looks as if you, or whoever wrote
the script, were print()'ing the value before you changed it to
system(), and forgot to change the arguments appropriately.)
> print ("New User $username has been successfully added!\n");
> print ("New User password: $password\n");
> print ("New User Home Directory: /home/sites/home/$username\n");
>
> open(OUTFILE,
> ">>/usr/local/private/platypusd/secure_dir/plat_adduser.log");
Again, you want to check the return value of open().
> print OUTFILE ("@calladduser");
> close(OUTFILE);
>
> I get an error of not such file or directory when the billing program
> calls this script to parse the file. I don't understand much about
> perl and I think the script is not looking for the file, maybe it
> doesn't know where the file to be parse is. I get an error of No such
> file or directory.
Consequently, this is *exactly* the kind of information you'd get if you
checked return values consistently. Also, the phrase "I get an error"
is about the worst way to ask for help. Do not simplify. Do not
paraphrase. Include the *exact* output. It most likely contains clues
that you may not notice, but we will. This is why we ask for it.
HTH,
Tim Hammerquist
--
Software is largely a service industry operating under the persistent
but unfounded delusion that it is a manufacturing industry.
-- Eric S. Raymond
------------------------------
Date: Tue, 28 Jun 2005 02:19:44 -0700
From: Joe Smith <joe@inwap.com>
Subject: Re: perl script
Message-Id: <eMCdnW5NtN2yi1zfRVn-ig@comcast.com>
lynn wrote:
> open (INFILE, "$ARGV[0]") or die "Can't open file $ARGV[0] $!\n"
Do not abuse double quotes like that.
open INFILE,$ARGV[0] or die "Can't open file $ARGV[0] $!\n"
or
$file = shift;
open INFILE,$file or die "Can't open file $file $!\n"
> Same here check to see if the command ran correctly!
>
> system ("@calladduser") or die " call to add user failed $!\n"
No.
1) system("@calladduser") operates differently from
system(@calladduser) if the array contains shell metacharacters.
2) system() returns the error code, which is true when there
was an error and false when no error.
3) For system(), use $? instead of $!.
system @calladduser and die "Error code $? from @calladduser\n";
or
system @calladduser == 0 or die "Error code $? from @calladduser\n";
-Joe
------------------------------
Date: 28 Jun 2005 07:22:23 GMT
From: tadmc@augustmail.com
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.5 $)
Message-Id: <42c0faa5$0$24838$8b463f8a@news.nationwide.net>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.5 $)
This newsgroup, commonly called clpmisc, is a technical newsgroup
intended to be used for discussion of Perl related issues (except job
postings), whether it be comments or questions.
As you would expect, clpmisc discussions are usually very technical in
nature and there are conventions for conduct in technical newsgroups
going somewhat beyond those in non-technical newsgroups.
The article at:
http://www.catb.org/~esr/faqs/smart-questions.html
describes how to get answers from technical people in general.
This article describes things that you should, and should not, do to
increase your chances of getting an answer to your Perl question. It is
available in POD, HTML and plain text formats at:
http://mail.augustmail.com/~tadmc/clpmisc.shtml
For more information about netiquette in general, see the "Netiquette
Guidelines" at:
http://andrew2.andrew.cmu.edu/rfc/rfc1855.html
A note to newsgroup "regulars":
Do not use these guidelines as a "license to flame" or other
meanness. It is possible that a poster is unaware of things
discussed here. Give them the benefit of the doubt, and just
help them learn how to post, rather than assume
A note about technical terms used here:
In this document, we use words like "must" and "should" as
they're used in technical conversation (such as you will
encounter in this newsgroup). When we say that you *must* do
something, we mean that if you don't do that something, then
it's unlikely that you will benefit much from this group.
We're not bossing you around; we're making the point without
lots of words.
Do *NOT* send email to the maintainer of these guidelines. It will be
discarded unread. The guidelines belong to the newsgroup so all
discussion should appear in the newsgroup. I am just the secretary that
writes down the consensus of the group.
Before posting to comp.lang.perl.misc
Must
This section describes things that you *must* do before posting to
clpmisc, in order to maximize your chances of getting meaningful replies
to your inquiry and to avoid getting flamed for being lazy and trying to
have others do your work.
The perl distribution includes documentation that is copied to your hard
drive when you install perl. Also installed is a program for looking
things up in that (and other) documentation named 'perldoc'.
You should either find out where the docs got installed on your system,
or use perldoc to find them for you. Type "perldoc perldoc" to learn how
to use perldoc itself. Type "perldoc perl" to start reading Perl's
standard documentation.
Check the Perl Frequently Asked Questions (FAQ)
Checking the FAQ before posting is required in Big 8 newsgroups in
general, there is nothing clpmisc-specific about this requirement.
You are expected to do this in nearly all newsgroups.
You can use the "-q" switch with perldoc to do a word search of the
questions in the Perl FAQs.
Check the other standard Perl docs (*.pod)
The perl distribution comes with much more documentation than is
available for most other newsgroups, so in clpmisc you should also
see if you can find an answer in the other (non-FAQ) standard docs
before posting.
It is *not* required, or even expected, that you actually *read* all of
Perl's standard docs, only that you spend a few minutes searching them
before posting.
Try doing a word-search in the standard docs for some words/phrases
taken from your problem statement or from your very carefully worded
"Subject:" header.
Really Really Should
This section describes things that you *really should* do before posting
to clpmisc.
Lurk for a while before posting
This is very important and expected in all newsgroups. Lurking means
to monitor a newsgroup for a period to become familiar with local
customs. Each newsgroup has specific customs and rituals. Knowing
these before you participate will help avoid embarrassing social
situations. Consider yourself to be a foreigner at first!
Search a Usenet archive
There are tens of thousands of Perl programmers. It is very likely
that your question has already been asked (and answered). See if you
can find where it has already been answered.
One such searchable archive is:
http://groups.google.com/advanced_group_search
If You Like
This section describes things that you *can* do before posting to
clpmisc.
Check Other Resources
You may want to check in books or on web sites to see if you can
find the answer to your question.
But you need to consider the source of such information: there are a
lot of very poor Perl books and web sites, and several good ones
too, of course.
Posting to comp.lang.perl.misc
There can be 200 messages in clpmisc in a single day. Nobody is going to
read every article. They must decide somehow which articles they are
going to read, and which they will skip.
Your post is in competition with 199 other posts. You need to "win"
before a person who can help you will even read your question.
These sections describe how you can help keep your article from being
one of the "skipped" ones.
Is there a better place to ask your question?
Question should be about Perl, not about the application area
It can be difficult to separate out where your problem really is,
but you should make a conscious effort to post to the most
applicable newsgroup. That is, after all, where you are the most
likely to find the people who know how to answer your question.
Being able to "partition" a problem is an essential skill for
effectively troubleshooting programming problems. If you don't get
that right, you end up looking for answers in the wrong places.
It should be understood that you may not know that the root of your
problem is not Perl-related (the two most frequent ones are CGI and
Operating System related), so off-topic postings will happen from
time to time. Be gracious when someone helps you find a better place
to ask your question by pointing you to a more applicable newsgroup.
How to participate (post) in the clpmisc community
Carefully choose the contents of your Subject header
You have 40 precious characters of Subject to win out and be one of
the posts that gets read. Don't waste them. Take care while
composing them, they are the key that opens the door to getting an
answer.
Spend them indicating what aspect of Perl others will find if they
should decide to read your article.
Do not spend them indicating "experience level" (guru, newbie...).
Do not spend them pleading (please read, urgent, help!...).
Do not spend them on non-Subjects (Perl question, one-word
Subject...)
For more information on choosing a Subject see "Choosing Good
Subject Lines":
http://www.cpan.org/authors/id/D/DM/DMR/subjects.post
Part of the beauty of newsgroup dynamics, is that you can contribute
to the community with your very first post! If your choice of
Subject leads a fellow Perler to find the thread you are starting,
then even asking a question helps us all.
Use an effective followup style
When composing a followup, quote only enough text to establish the
context for the comments that you will add. Always indicate who
wrote the quoted material. Never quote an entire article. Never
quote a .signature (unless that is what you are commenting on).
Intersperse your comments *following* each section of quoted text to
which they relate. Unappreciated followup styles are referred to as
"top-posting", "Jeopardy" (because the answer comes before the
question), or "TOFU" (Text Over, Fullquote Under).
Reversing the chronology of the dialog makes it much harder to
understand (some folks won't even read it if written in that style).
For more information on quoting style, see:
http://web.presby.edu/~nnqadmin/nnq/nquote.html
Speak Perl rather than English, when possible
Perl is much more precise than natural language. Saying it in Perl
instead will avoid misunderstanding your question or problem.
Do not say: I have variable with "foo\tbar" in it.
Instead say: I have $var = "foo\tbar", or I have $var = 'foo\tbar',
or I have $var = <DATA> (and show the data line).
Ask perl to help you
You can ask perl itself to help you find common programming mistakes
by doing two things: enable warnings (perldoc warnings) and enable
"strict"ures (perldoc strict).
You should not bother the hundreds/thousands of readers of the
newsgroup without first seeing if a machine can help you find your
problem. It is demeaning to be asked to do the work of a machine. It
will annoy the readers of your article.
You can look up any of the messages that perl might issue to find
out what the message means and how to resolve the potential mistake
(perldoc perldiag). If you would like perl to look them up for you,
you can put "use diagnostics;" near the top of your program.
Do not re-type Perl code
Use copy/paste or your editor's "import" function rather than
attempting to type in your code. If you make a typo you will get
followups about your typos instead of about the question you are
trying to get answered.
Provide enough information
If you do the things in this item, you will have an Extremely Good
chance of getting people to try and help you with your problem!
These features are a really big bonus toward your question winning
out over all of the other posts that you are competing with.
First make a short (less than 20-30 lines) and *complete* program
that illustrates the problem you are having. People should be able
to run your program by copy/pasting the code from your article. (You
will find that doing this step very often reveals your problem
directly. Leading to an answer much more quickly and reliably than
posting to Usenet.)
Describe *precisely* the input to your program. Also provide example
input data for your program. If you need to show file input, use the
__DATA__ token (perldata.pod) to provide the file contents inside of
your Perl program.
Show the output (including the verbatim text of any messages) of
your program.
Describe how you want the output to be different from what you are
getting.
If you have no idea at all of how to code up your situation, be sure
to at least describe the 2 things that you *do* know: input and
desired output.
Do not provide too much information
Do not just post your entire program for debugging. Most especially
do not post someone *else's* entire program.
Do not post binaries, HTML, or MIME
clpmisc is a text only newsgroup. If you have images or binaries
that explain your question, put them in a publically accessible
place (like a Web server) and provide a pointer to that location. If
you include code, cut and paste it directly in the message body.
Don't attach anything to the message. Don't post vcards or HTML.
Many people (and even some Usenet servers) will automatically filter
out such messages. Many people will not be able to easily read your
post. Plain text is something everyone can read.
Social faux pas to avoid
The first two below are symptoms of lots of FAQ asking here in clpmisc.
It happens so often that folks will assume that it is happening yet
again. If you have looked but not found, or found but didn't understand
the docs, say so in your article.
Asking a Frequently Asked Question
It should be understood that you may have missed the applicable FAQ
when you checked, which is not a big deal. But if the Frequently
Asked Question is worded similar to your question, folks will assume
that you did not look at all. Don't become indignant at pointers to
the FAQ, particularly if it solves your problem.
Asking a question easily answered by a cursory doc search
If folks think you have not even tried the obvious step of reading
the docs applicable to your problem, they are likely to become
annoyed.
If you are flamed for not checking when you *did* check, then just
shrug it off (and take the answer that you got).
Asking for emailed answers
Emailed answers benefit one person. Posted answers benefit the
entire community. If folks can take the time to answer your
question, then you can take the time to go get the answer in the
same place where you asked the question.
It is OK to ask for a *copy* of the answer to be emailed, but many
will ignore such requests anyway. If you munge your address, you
should never expect (or ask) to get email in response to a Usenet
post.
Ask the question here, get the answer here (maybe).
Beware of saying "doesn't work"
This is a "red flag" phrase. If you find yourself writing that,
pause and see if you can't describe what is not working without
saying "doesn't work". That is, describe how it is not what you
want.
Sending a "stealth" Cc copy
A "stealth Cc" is when you both email and post a reply without
indicating *in the body* that you are doing so.
Be extra cautious when you get upset
Count to ten before composing a followup when you are upset
This is recommended in all Usenet newsgroups. Here in clpmisc, most
flaming sub-threads are not about any feature of Perl at all! They
are most often for what was seen as a breach of netiquette. If you
have lurked for a bit, then you will know what is expected and won't
make such posts in the first place.
But if you get upset, wait a while before writing your followup. I
recommend waiting at least 30 minutes.
Count to ten after composing and before posting when you are upset
After you have written your followup, wait *another* 30 minutes
before committing yourself by posting it. You cannot take it back
once it has been said.
AUTHOR
Tad McClellan <tadmc@augustmail.com> and many others on the
comp.lang.perl.misc newsgroup.
------------------------------
Date: Tue, 28 Jun 2005 07:44:14 +0200
From: "Tassilo v. Parseval" <tassilo.von.parseval@rwth-aachen.de>
Subject: Re: Simple Structure Question
Message-Id: <slrndc1ote.qa.tassilo.von.parseval@localhost.localdomain>
Also sprach one man army:
> You know why All Five of you men are so cool, because You Read The
> Manual! All 800+ pages of gnarly, dense, encoded hard-core Perl. You
> have worked so hard at reading the manual, that you cannot wait to leap
> out, virutally in unison, with a shouts of "Read the Manual!"
I never quite understood why some people get so antagonized by pointers
to the reference documentation. Parts of it are actually quite well
written with beginners in mind. I learnt Perl by using two sources
of information: A very cursory reference found in "Linux in a Nutshell"
(which only lists all Perl language constructs in tables without any
explanations) and the standard Perl documentation. Obviously, it
makes little sense to read the latter from the start to the end
(especially since it has no marked entry-point). Rather read only those
parts that concern you and your problem. Those were the ones you were
pointed to here. Concidering the vast amount of Perl manpages (134 as of
5.8.4), this is quite a valuable information not easy deducible for a
beginner.
> I admit it, after 2 straight 15 hour plus research days, on a completely
> unrelated topic, I though I could get a Perl program running to just
> read the contents of 840 links on a web page. I read the manual, I went
> to CPAN, I installed the module, and it worked! That's why you guys are
> worth it, 'cause your language does work.
>
> But in the Beginners Perl Book I have, there is no discussion of this
> terse syntax I encountered, so yes, I asked for someone to help and
> explain it. It was weak, there were _more manuals_ I could have read
> first.
Not more manuals but rather the relevant ones.
> The post that is really the indicator of them all I think is Tassilo's
> with the .sig that says "use bigint;
> $n=71423350343770280161397026330337371139054411854220053437565440;
> $m=-8,;;$_=$n&(0xff)<<$m,,$_>>=$m,,print+chr,,while(($m+=8)<=200);"
>
> I have worked as a C programmer for 15 years. I have written and shipped
> and rev'ed huge commercial applications. You will never, ever, ever find
> code like that in any file, ever. It is considered Bad Practice, for
> good reasons.
As is the obfuscated C contest with which you should be familiar
considering your 15 years of C experience. These contests as well as
obfuscated signatures are nothing else than a self-ironic view on some
of the shortcomings certain languages have, namely the tendency towards
a very terse and at times even cryptic syntax. It should be out of the
question that anyone (me anyway) would ever allow lines like that to slip
into production code.
> This Perl group is absolutely reflective of the traditional UNIX
> culture, dense, terse, sup smart CRYPTO code. If you can't read it, what
> are you doing here - you have manuals to read!!
Why, we already have read them. ;-)
> I am going to have a look at arrays of hashes actually, because I really
> do want to be able to read this web page. I got a good day/night of
> rest. But I don't have months to just study Perl. So I thought if
> someone wanted to try to explain the construct, they could. The post was
> hasty, I admit it. Thank you for the DataDumper pointer. I am used to a
> header file with a struct definition, but I am not there in Perl.
There might not even be such a definition in Perl. All Perl
data-structures grow as needed. New key/value pairs may always be added
to a hash so the way of working in Perl is quite different from the way
you may have learnt in C where you usually have a couple of other editor
sessions in order to see some headers.
Tassilo
--
use bigint;
$n=71423350343770280161397026330337371139054411854220053437565440;
$m=-8,;;$_=$n&(0xff)<<$m,,$_>>=$m,,print+chr,,while(($m+=8)<=200);
------------------------------
Date: Tue, 28 Jun 2005 08:15:49 +0200
From: "Tassilo v. Parseval" <tassilo.von.parseval@rwth-aachen.de>
Subject: Re: Simple Structure Question
Message-Id: <slrndc1qol.qa.tassilo.von.parseval@localhost.localdomain>
Also sprach one man army:
> ok, so it looked like perhaps HTML::LinkExtractor was going to be easier
> to use. So I run a simple loop, as per the examples. I get a Hash? Hash
> ref? back in each iteration. DataDumper shows something like (below). By
> Reading the Manual, I infer to choose only a $ThisLink with an 'href'
> entry, I use
> if ( exists $ThisLink{ href } ) { ... }
>
> But I always get back an UNDEF for every iteration... I tried
> @$ThisLink{ href} just for kicks, but that doesn't work either... Any
> insights to get me past this sticking point?
Throwing guess-work at the Perl interpreter is not likely to work out on
the long run. What you need is to familiarize yourself with a few
fundamental concepts behind references. You must have gone through a
similar process in the past with structures and pointer to structures in
C. The good news is that references in Perl are easier to understand so
you will need much less time for those as for the related C concepts.
>
> thanks in advance
>
> ##--
> my $LX = new HTML::LinkExtractor();
> $LX->parse( $FileName);
>
> for $ThisLink( @{ $LX->links } ) {
> print "ThisLink = " . Dumper( $ThisLink );
> if ( exists $ThisLink{ href } ) {
> print "LinkInner = " . $ThisLink{ href } . "\n";
> }
> }
The first thing to notice is that Dumper() doesn't work on hashes or
arrays but on references to them. The C analogy:
struct foo a;
Dumper(a); /* wrong */
Dumper(&a); /* right */
Subsequently, if you have a plain hash (indicated by the sigil '%' in
front of the variable name instead of '$', that is: %ThisLink):
print Dumper(%ThisLink); # wrong
print Dumper(\%ThisLink); # right
So Perl's '\' is roughly equivalent to C's '&'. Only roughly because a
Perl reference is not a memory-address as returned by C's '&'.
> ThisLink = $VAR1 = {
> 'content' => 'text/html; charset=iso-8859-1',
> 'tag' => 'meta',
> 'http-equiv' => 'Content-Type'
> };
Again many indications that you are not dealing with a plain hash. The
curly braces '{' and '}' are a hash-reference constructor. '[' and ']'
are the constructor for array-references and plain parens '(' and ')'
can be regarded as list-constructor (technically not quite correct but
good enough):
my $hash_ref = { key => 'value' };
my %hash = ( key => 'value' );
my $ary_ref = [ 1, 2, 3 ];
my @ary = ( 1, 2, 3 );
The nice thing about reference types in Perl is that accessing single
elements is similar to how it is done in C, i.e. by using the '->'
operator:
typedef struct {
int a;
} foo;
...
foo *f = return_foo_struct(...);
printf("%i\n", f->a);
In Perl:
my $f = { a => 1 };
print $f->{a};
If $f was an array-reference:
my $f = [ 1, 2, 3 ];
print $f->[0];
If you have non-reference arrays or hashes, the arrow is simply dropped:
my %f = ...;
print $f{a};
my @f = ...;
print $f[0];
The '$' sigil in the subscript expressions is not a mistake. It means
that the whole expression (both $f{a} and $f[0]) is a scalar.
This is most likely all you need to know for your problem at hand. It
is, however, not all about references. There are ways to turn hash- and
array-references back into plain hashes and arrays. This is all layed
out nicely in the documentation that you should feel less compelled
about to read. Aside from the already mentioned ones 'perlreftut' will
give you three simple rules that will help you in every situation a
reference shows up somehow.
Tassilo
--
use bigint;
$n=71423350343770280161397026330337371139054411854220053437565440;
$m=-8,;;$_=$n&(0xff)<<$m,,$_>>=$m,,print+chr,,while(($m+=8)<=200);
------------------------------
Date: Tue, 28 Jun 2005 02:57:36 -0700
From: Joe Smith <joe@inwap.com>
Subject: Re: Simple Structure Question
Message-Id: <F9GdnX2YG8mLglzfRVn-oA@comcast.com>
one man army wrote:
> Can someone explain this line?
>
> while ( $token = $p->get_tag("a")) {
> $url = $token->[1]{href} || "-";
>
> $token is now a struct,
You should use the proper vocabulary. $token is a reference
to an array of hashes.
> with a first element that has a string,
The first element may or may not be a string, since you haven't
shown how $token->[0] is used. (First = 0, not 1.)
> but {href} refers to a pattern that may occur, which returns a true or false?
No, 'href' is a key into the %{$token->[1]} hash. If the value
corresponding to the keys is undefined or zero or "0", then the
value of "-" will be used.
> Can someone write a 2 line synonym that is not so terse?
Skipping the while() part:
$ref_to_array_of_hashes = class_of_p::get_tag('a');
@array_of_hashes = @{$ref_to_array_of_hashes};
$ref_to_hash = $array_of_hashes[1];
%hash = %{$ref_to_hash};
$url = $hash{'href'};
$url = '-' unless $url;
-Joe
------------------------------
Date: Tue, 28 Jun 2005 06:35:07 +0200
From: Fabian Pilkowski <pilkowsk@informatik.uni-marburg.de>
Subject: Re: Typeglob Qs
Message-Id: <3ic29kFkpa6kU1@individual.net>
* kj schrieb:
> What is the connection, if any, between typeglobs and references
> to package variables? The following debugger interaction suggests
> that they are very similar:
>
> DB<1> $x = 'foobar'
> DB<2> $y = *::x
> DB<3> p $$y
> foobar
> DB<4> $z = \$::x
> DB<5> p $$z
> foobar
>
> Is this similarity of behavior superficial?
Here, the typeglob is doing more. Not only the SCALAR slot in the symbol
table entry is altered. Example for ARRAY:
#!/usr/bin/perl -w
@x = qw( 1 2 3 );
$x = 'foobar';
$y = *x;
print $$y, "\n";
print @$y, "\n";
$z = \$x;
print $$z, "\n";
print @$z, "\n";
__END__
After doing "$y=*x" you could also run a subroutine &x() by calling
&$y(). You say something like: "all that is accessible via 'x' I want
access via $y too".
In the second case you just say: "make $z a reference to the scalar slot
of x". AFAIK it has the same effect as calling "$z=*x{SCALAR}".
>
> Also, how can one retrieve the dirhandle, socket, and format items
> from a typeglob. I'm aware of the *x{THING} syntax, but it's not
> clear to me what value to use inside the curlies to access the
> items listed.
The way I understand `perldoc perlref` the THING could be one of
SCALAR, ARRAY, HASH, CODE, IO, or GLOB. Nothing else. *foo{THING}
returns a reference to the THING slot in *foo. I read (shortened):
*foo{IO} ... It returns the IO handle, used for file handles,
sockets, and directory handles.
In other words there is only one IO handle (singular) for all these
types. The referenced page `perldoc -f opendir` says:
DIRHANDLEs have their own namespace separate from FILEHANDLEs.
Combining all of this together: I think you could grab only one IO
reference from a specific symbol table entry. But you could use the
*same* one for different things like open/opendir/socket at the same
time. There is no problem due to separated namespaces, and Perl is
deciding which handle is to use. Feel free to make a test script for
this.
regards,
fabian
------------------------------
Date: Tue, 28 Jun 2005 15:51:10 +1000
From: "Sisyphus" <sisyphus1@nomail.afraid.org>
Subject: Re: Typeglob Qs
Message-Id: <42c0e554$0$16490$afc38c87@news.optusnet.com.au>
"kj" <socyl@987jk.com.invalid> wrote in message
news:d9qd07$hu$1@reader1.panix.com...
>
>
>
> What is the connection, if any, between typeglobs and references
> to package variables? The following debugger interaction suggests
> that they are very similar:
>
> DB<1> $x = 'foobar'
> DB<2> $y = *::x
> DB<3> p $$y
> foobar
> DB<4> $z = \$::x
> DB<5> p $$z
> foobar
>
> Is this similarity of behavior superficial?
A Devel::Peek::Dump() can be useful here:
--- try.pl ---
use warnings;
use Devel::Peek;
$x = 'foobar';
$y = *::x;
$z = \$::x;
Dump($y);
print "#############\n";
Dump($z);
__END__
produces:
SV = PVGV(0x8eadc4) at 0x3f5e38
REFCNT = 1
FLAGS = (GMG,SMG,FAKE,MULTI)
IV = 0
NV = 0
MAGIC = 0x893124
MG_VIRTUAL = &PL_vtbl_glob
MG_TYPE = PERL_MAGIC_glob(*)
MG_OBJ = 0x3f5e38
NAME = "x"
NAMELEN = 1
GvSTASH = 0x3f5040 "main"
GP = 0x8a208c
SV = 0x3f5e14
REFCNT = 2
IO = 0x0
FORM = 0x0
AV = 0x0
HV = 0x0
CV = 0x0
CVGEN = 0x0
GPFLAGS = 0x0
LINE = 4
FILE = "try.pl"
FLAGS = 0x2
EGV = 0x3f5e44 "x"
#############
SV = RV(0x8db044) at 0x3f5e8c
REFCNT = 1
FLAGS = (ROK)
RV = 0x3f5e14
SV = PV(0x3f5ff4) at 0x3f5e14
REFCNT = 2
FLAGS = (POK,pPOK)
PV = 0x8933c4 "foobar"\0
CUR = 6
LEN = 7
Cheers,
Rob
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
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