[27791] in Perl-Users-Digest
Perl-Users Digest, Issue: 9155 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Fri Apr 14 09:05:44 2006
Date: Fri, 14 Apr 2006 06:05:03 -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 Fri, 14 Apr 2006 Volume: 10 Number: 9155
Today's topics:
existence and size of client file <no@thanks.com>
Re: existence and size of client file <jurgenex@hotmail.com>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@augustmail.com
Re: tr/// broken? <rvtol+news@isolution.nl>
Re: XS progamming question <bol@adv.magwien.gv.at>
Re: XS progamming question <bol@adv.magwien.gv.at>
Re: XS progamming question <bol@adv.magwien.gv.at>
Re: XS progamming question (Anno Siegel)
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Fri, 14 Apr 2006 14:00:38 +0200
From: Asterbing <no@thanks.com>
Subject: existence and size of client file
Message-Id: <MPG.1ea9ad53ca866c6a9897e6@news.tiscali.fr>
Is there a way to test the existence and size of a client file ? This to
avoid any unuseful traffic (upload, serveur file test, unlink if too
big) and report to user as fast as possible (upload limit being high in
some cases I've to treat ; some tenth of MB).
------------------------------
Date: Fri, 14 Apr 2006 12:09:14 GMT
From: "Jürgen Exner" <jurgenex@hotmail.com>
Subject: Re: existence and size of client file
Message-Id: <KhM%f.20266$wH1.3677@trnddc03>
Asterbing wrote:
> Is there a way to test the existence and size of a client file ?
Depending on what kind of client you are talking about, maybe. Like for
mirroring systems that's a key functionality.
But what does that have to do with Perl?
jue
------------------------------
Date: 14 Apr 2006 07:22:14 GMT
From: tadmc@augustmail.com
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.5 $)
Message-Id: <443f4da6$0$61163$ae4e5890@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: Fri, 14 Apr 2006 12:58:44 +0200
From: "Dr.Ruud" <rvtol+news@isolution.nl>
Subject: Re: tr/// broken?
Message-Id: <e1o6ak.190.1@news.isolution.nl>
Ilya Zakharevich schreef:
> [A complimentary Cc of this posting was sent to
> Dr.Ruud
Please don't do that. This is a newsgroup. Even with mailing lists I
wouldn't do that, unless it is specifically requested somehow.
> rvtol:
>> In a Perl context, 'utf8' is commonly read as the proper subset of
>> 'UTF-8' currently used by Perl.
>
> utf8 is a proper SUPERSET of UTF-8.
Yes, sorry. When I wrote that I had a huge headache, that has just left
together with one of my wisdom teeth.
> The former is not restricted to
> any particular range of non-negative integers; the current
> implementation goes 0..0xFFFFFFFFFFFFFFFF (i.e., maximal range of
> native unsigned integers currently used in Perl), and there are "free"
> bits to extend it to, e.g., 128bit - if Perl is used on architecture
> with sizeof(UV) = 128bits.
>
> UTF-8 is "legally" restricted to 0..0x1FFFFF, although technically, it
> can cover up to, IIRC, 0..0x1FFFFFFF.
OK, thanks.
--
Affijn, Ruud
"Gewoon is een tijger."
------------------------------
Date: Fri, 14 Apr 2006 11:00:53 +0200
From: "Ferry Bolhar" <bol@adv.magwien.gv.at>
Subject: Re: XS progamming question
Message-Id: <1145005253.970113@proxy.dienste.wien.at>
robic0:
> Is this '*' used here a 'glob'?
Yes.
> Can you explain in detail just what a glob is?
I'll try it - everyone is kindly invited to correct/supplement my
explantation:
A typeglob is a data structure containing references (pointers) to various
kind of
'values': scalars, arrays, hashes, codes, and data structures representing
file
handles and forms.
For each of these pointers, a typeglob contains a slot. If you say "@x",
Perl first looks in the %main:: hash (the "main" namespace or default
package)
for the key "x" - in other words, it looks for the value of "$main::{x}".
This is
a typeglob and now, because of the "@", Perl looks in the array slot of the
typelob to locate the array "@x" (the AV = array value for "x").
Writung
@x = (1,2,3)
is just a another way for writing
*x = [1,2,3];
Using the [...], you create an array reference and assign it to the array
slot in
typeglob "x", yielding the array variable "@x". In other words, "@x" is just
a dereference operation of the array reference stored in typeglobs "x" array
slot.
And, in a similar way, you can write
*x = {key => 'val'};
as another way for
%h = (key => 'val');
Because typeglobs contain references, the only way in Pre-5 Perl-versions
to pass references was to use typeglobs. For example, in Perl 4, where the
reference operator "\" did not yet exist, one could write
@array_1 = (....);
@array_2 = (....);
my_func(*array_1, *array_2);
sub my_func {
(*xx,*yy) = @_;
... # Now one can access the arrays as @xx and @yy
}
And because Perl provides no way to name IO handles directly and
therefore to pass them to subs (at least until 5.6), one can use typeglobs
for this as well:
open OUT,'>x.x';
do_write(*OUT);
...
sub do_write {
*fh = shift;
print fh "This goes to x.x!\n";
}
The most use of typeglobs nowadays is aliasing (e.g., by the Exporter
module):
*foo = *mod::bar;
makes all foo similar to all bar in the 'mod' package. Internally, the
stashes for "foo" and "mod::bar" will point to the same typeglob slot
structure.
And I think this was the only reason that these data structures, which
are else used only internally in conjunction with stashes (symbol table
hashes, see the "main:: example" above) were made visible form Perl.
'*x' is often mentioned as "all from x", but actually means "this from x
what is currently required". So, as shown in the examples above, if
you pass an array reference to a typeglob, it is stored in its array slot,
if you pass a hash reference, it is stored in the typeglobs hash slot,
and so on, but you have always to write simply "*x" only.
You can write
*x{ARRAY}
to access the array entry in typeglob x. This returns the reference to
the array value, if one exists. Therefore, saying
$arref = *x{ARRAY};
is the Perl4 equivalent of
$arref = \@x;
And
@{*x{ARRAY}}
is a somewhat interesting way to write
@x.
The *x{ARRAY} syntax and friends is a way to access a typeglob's
slots from Perl and to allow a Perl script to find out which slot (or slots)
are used. This allows Perl code to dump out parts of or the entire symbol
table of a package. The Perl debugger and the Data::Dumper module
make use of this.
A typeglob itself is treated as scalar value and therefore can be stored
in a scalar and can be passed like any other scalar value (as shown in
the examples above). However, typeglobs are used for package variables
only, not for lexical variables (which are implemented by scratch pads),
and therefore a declaration like
my *x;
is not valid.
One last thing: passing a scalar reference to a typeglob marks the
scalar value as read-only (the well-known example from the Perl docs):
*PI = \3.1415;
makes the scalar $PI contain the unchangeable value of pi. But this is
just a goodie of Perl, it has nothing to do with typeglobs. Using XS,
you can mark every scalar value as read-only (and even could set
the above value to writeable again).
OK, Perl experts: (Ilya, Xho, and others): how about this?
Greetings, Ferry
--
Ing. Ferry Bolhar
Municipality of Vienna, Department 14
A-1010 Vienna / AUSTRIA
E-mail: bol@adv.magwien.gv.at
------------------------------
Date: Fri, 14 Apr 2006 11:50:20 +0200
From: "Ferry Bolhar" <bol@adv.magwien.gv.at>
Subject: Re: XS progamming question
Message-Id: <1145008221.22187@proxy.dienste.wien.at>
Ilya Zakharevich:
>> Can you explain in detail just what a glob is?
>
> You do not want to know. Just avoid them at any cost; they are just
> remnants of object-less Perl4.
Not only. Or is there another way for aliasing in Perl5?
But I would guess there is no much use for typeglobs in XS progamming,
right?
Greetings, Ferry
--
Ing. Ferry Bolhar
Municipality of Vienna, Department 14
A-1010 Vienna / AUSTRIA
E-mail: bol@adv.magwien.gv.at
------------------------------
Date: Fri, 14 Apr 2006 12:15:43 +0200
From: "Ferry Bolhar" <bol@adv.magwien.gv.at>
Subject: Re: XS progamming question
Message-Id: <1145009743.823891@proxy.dienste.wien.at>
Ilya Zakharevich:
> This is a shortcut for
>
> *mysub{CODE}->();
OK. Let's see whether I understood:
mysub();
generates the code to access the CODE entry in typeglob *mysub,
even if this entry is currently - at compile time - yet empty. Later,
when
sub mysub{...}
is encountered, the sub is compiled, a CV is generated and its address
is stored in *mysubs CODE entry - this occurs all in the compilation
phase. So, because both invocations of mysub access the same typeglob's
CODE entry, the lexical order of the invocations isn't relevant, as long as
they do not appeart inside BEGINs.
> Yes. The "content of sub" is compiled in a different package. The
> second code is equivalent to
>
> package foo;
>
> $var = 1;
> sub bar {
> package main;
> ...
> };
Well, lets say: would it be equivalent if each identifier within "bar" would
be
prefixed with "foo"? Or in other words: does "package" has any effect
at run-time?
> > IIUC 'package' is just a compiler directive (like 'use', 'my' and
'our'),
> > never appearing in an OP tree?
>
> There is a notion of "current package" during execution (relevant to,
> at least, eval"" and caller() [what else?]). So it IS stored in the
> compile tree.
But where? Which OP is used for "package"?
I tried to run a program with -MO=Concise,-exec with and without
"package" but couldn't see any difference (besides the leading package
name in each "gvsv" or "gv" OP´). What are the indications of "package"
at run-time?
Greetings, Ferry
--
Ing. Ferry Bolhar
Municipality of Vienna, Department 14
A-1010 Vienna / AUSTRIA
E-mail: bol@adv.magwien.gv.at
------------------------------
Date: 14 Apr 2006 12:02:56 GMT
From: anno4000@lublin.zrz.tu-berlin.de (Anno Siegel)
Subject: Re: XS progamming question
Message-Id: <4a9hbgFrmpgvU1@news.dfncis.de>
Ferry Bolhar <bol@adv.magwien.gv.at> wrote in comp.lang.perl.misc:
> Ilya Zakharevich:
>
> >> Can you explain in detail just what a glob is?
> >
> > You do not want to know. Just avoid them at any cost; they are just
> > remnants of object-less Perl4.
>
> Not only. Or is there another way for aliasing in Perl5?
Yes. For a lexical alias to a package variable, there's
our( $package_variable);
though you don't get to choose a name for the alias, it's always the name
of the package variable without the package specification. Like glob
aliasing, this works for scalars, arrays and hashes.
Another way is through a "for" loop:
for $alias ( $orig ) {
# $alias is an alias to $orig here
}
This only works for scalars but is unrestricted in other ways: both
$alias and $orig can be either lexical or package variables. The alias
is restricted to one block, which is often an advantage, but gets
inconvenient when you want many aliases.
So, TIMTOWTDI all around.
> But I would guess there is no much use for typeglobs in XS progamming,
> right?
As in Perl code, dealing with typeglobs happens with legacy code that
uses them for some reason. There is nothing attractive you can do with
typeglobs (in XS or Perl) that you can't do without them.
"Lexical filehandles" may seem to be an exception, but there you don't
deal with globs but with globrefs which behave like any other ref. The
behavior of globs proper doesn't enter the picture.
Anno
--
If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers.
------------------------------
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)
Message-Id: <null>
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#For other requests pertaining to the digest, send mail to
#perl-users-request@ruby.oce.orst.edu. Do not waste your time or mine
#sending perl questions to the -request address, I don't have time to
#answer them even if I did know the answer.
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End of Perl-Users Digest V10 Issue 9155
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