[31906] in Perl-Users-Digest
Perl-Users Digest, Issue: 3169 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Oct 12 06:09:25 2010
Date: Tue, 12 Oct 2010 03:09:05 -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, 12 Oct 2010 Volume: 11 Number: 3169
Today's topics:
Re: Communication across Perl scripts <xhoster@gmail.com>
Re: Communication across Perl scripts <m@rtij.nl.invlalid>
Re: Communication across Perl scripts <peter@makholm.net>
Re: Date difference in days <paul@pstech-inc.com>
Re: FAQ 4.42 How can I tell whether a certain element i <ben@morrow.me.uk>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: toy list processing problem: collect similar terms <es@ertes.de>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Mon, 11 Oct 2010 17:27:01 -0700
From: Xho Jingleheimerschmidt <xhoster@gmail.com>
Subject: Re: Communication across Perl scripts
Message-Id: <4cb3be04$0$20746$ed362ca5@nr5-q3a.newsreader.com>
Jean wrote:
> I am searching for efficient ways of communication across two Perl
> scripts. I have two scripts; Script 1 generates some data. I want my
> script two to be able to access that information. The easiest/dumbest
> way is to write the data generated by script 1 as a file and read it
> later using script 2.
This is usual not dumb. It is often the best way to do it.
Intermediate files and shell pipelines are by far the most common way
for me to do this--I never use anything other than those two unless I
have a compelling reason. Maybe you have a compelling reason, I don't
know and you haven't given us enough information to determine.
(Well, the third default option is to reconsider whether these two
scripts really need to be different rather than one script. I assume
you already did that rejected it for some good reason.)
> Is there any other way than this ? Can I store
> the data in memory and make it available to script two (of-course with
> support from my Linux ) ? Meaning malloc somedata by script 1 and make
> script 2 able to access it.
There are many ways to do this, and AFAIK they all either leave a lot to
be desired, or introduce annoying and subtle complexities.
> There is no guarantee that Script 2 will be run after Script 1. So
> there should be some way to free that memory using a watchdog timer.
Can't you control the timing of the execution of your scripts?
Xho
------------------------------
Date: Tue, 12 Oct 2010 08:23:59 +0200
From: Martijn Lievaart <m@rtij.nl.invlalid>
Subject: Re: Communication across Perl scripts
Message-Id: <vgbdo7-2l5.ln1@news.rtij.nl>
On Mon, 11 Oct 2010 19:55:03 -0500, Ted Zlatanov wrote:
> On Mon, 11 Oct 2010 22:14:29 +0200 Martijn Lievaart <m@rtij.nl.invlalid>
> wrote:
>
> ML> On Mon, 11 Oct 2010 14:17:58 -0500, Ted Zlatanov wrote:
>>> If you need low latency, use a message queue.
>
> ML> Speaking of message queues, what do people recommend on Unix/Linux?
>
> I've heard positive things about http://www.rabbitmq.com/ but haven't
> used it myself. There's a lot of others, see
> http://en.wikipedia.org/wiki/Category:Message-oriented_middleware
Thanks, I'll look into it.
M4
------------------------------
Date: Tue, 12 Oct 2010 10:05:57 +0200
From: Peter Makholm <peter@makholm.net>
Subject: Re: Communication across Perl scripts
Message-Id: <87k4lnygwq.fsf@vps1.hacking.dk>
"jl_post@hotmail.com" <jl_post@hotmail.com> writes:
> That may be easiest, but I don't think it's the dumbest. And if
> you use this approach, I highly recommend using the "Storable" module
> (it's a standard module so you should already have it).
As long as you just use it for a single host for very temporary files,
Storable is fine. But I have been bitten by Storable not being
compatible between versions or different installations one time to
many to call it 'highly recommended'.
If you need suport for every possible perl structure then Storable is
probably the only almost viable solution. But if simple trees of
hashrefs and arrayrefs is good enough the I consider JSON::XS a better
choice.
But it all depends on the exact needs and for the original poster he
might not come in situations where Storable shows it's nasty sides and
don't need the extra speed from JSON::XS or the more future-proofe and
portable format.
//Makholm
------------------------------
Date: Tue, 12 Oct 2010 02:58:29 -0400
From: "Paul E. Schoen" <paul@pstech-inc.com>
Subject: Re: Date difference in days
Message-Id: <BGTso.28092$Ib3.2057@newsfe21.iad>
"J. Gleixner" <glex_no-spam@qwest-spam-no.invalid> wrote in message
news:4cb31756$0$2511$815e3792@news.qwest.net...
> Paul E. Schoen wrote:
> [...]
>> The script can be seen in action as the hit counter in:
> [...]
>
> perldoc -q "I still don't get locking."
Yes, I read that (although I had to log in to my server with telnet, which
is inconvenient from a Win Vista machine).
This is the relevant code.
open (LOG, '<', "$logpath");
my @file = <LOG>; # an array of the file contents
close(LOG);
my $count = $file[0]; # the count value is the first line in the file,
i.e. $file[0]
$count++; # increments the counter value
open (LOG, ">$logpath"); # opens the log file for writing
flock(LOG, 2); # file lock set
print LOG "$count\n"; # prints out the new counter value to the file
flock(LOG, 8); # file lock unset
close(LOG);
This was from an existing script. I suppose I should check for return values
and use descriptive constants, but otherwise I don't see a problem. The
other information I found was:
http://perldoc.perl.org/functions/flock.html
BTW this webpage gets about 12 hits per day. Not much chance of a collision,
and probably not much damage if it happens. Losing count of a hit is not a
real problem, and I can accept a few "false" hits from bots. What would be
really useful would be to access the server log and sort out hits that don't
"count" such as those I create by testing, or those from automated web
crawlers or multiple hits from the same source.
And I understand that the hit counter is not perfect, but it does work to
some extent and at least we can get a general idea of the usage of the
website by our members, so we can determine if it is worthwhile to put more
effort into it at all. I implemented an event submission form and I have
only received notification from one member who used it as a trial. I also
have the framework of implementing the Google Calendar but it will take a
lot of work to allow members to enter, edit, and delete information. Or I
could just give them my login and password for that account (which I opened
specifically for that purpose).
I think the argument against hit counters is really splitting hares, and
that's pretty rough on the rabbits.
Paul
------------------------------
Date: Tue, 12 Oct 2010 06:10:37 +0100
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: FAQ 4.42 How can I tell whether a certain element is contained in a list or array?
Message-Id: <d77do7-vfe2.ln1@osiris.mauzo.dyndns.org>
Quoth PerlFAQ Server <brian@theperlreview.com>:
>
> That being said, there are several ways to approach this. In Perl 5.10
> and later, you can use the smart match operator to check that an item is
> contained in an array or a hash:
>
> use 5.010;
>
> if( $item ~~ @array )
> {
> say "The array contains $item"
> }
Is it worth being clearer that this checks if anything in @array
*smartmatches* $item? This can have some surprising consequences, such
as
~% perl -E'my @x = (" +001.0"); my $x = "1"; $x + 0; say $x ~~ @x'
1
which is certainly not what I would mean by 'contained in the array'.
(The fact that the '$x + 0' makes a difference I would have to consider
an outright bug, just as it is with the bitops.)
Ben
------------------------------
Date: Tue, 12 Oct 2010 02:07:01 -0500
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <Mc6dnTADVsqIlCnRnZ2dnUVZ5tadnZ2d@giganews.com>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
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://www.rehabitation.com/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 that they do
know and are being the "bad kind" of Lazy.
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_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 and many others on the comp.lang.perl.misc newsgroup.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.
------------------------------
Date: Tue, 12 Oct 2010 04:37:04 +0200
From: Ertugrul =?UTF-8?B?U8O2eWxlbWV6?= <es@ertes.de>
Subject: Re: toy list processing problem: collect similar terms
Message-Id: <20101012043704.66caa73b@tritium.streitmacht.eu>
"Peter J. Holzer" <hjp-usenet2@hjp.at> wrote:
> On 2010-10-08 22:22, Ertugrul S=C3=B6ylemez <es@ertes.de> wrote:
> > Josef <e9427749@stud4.tuwien.ac.at> wrote:
> >> Am 08.10.2010 04:38, schrieb Ertugrul S=C3=B6ylemez:
> >> > Josef<e9427749@stud4.tuwien.ac.at> wrote:
> >> >> I don't know the reason of the silence,
> >> >> but if anybody of the c.l.f people indeed fall sick.
> >> >> This time the code example is attempt for resuscitation, or
> >> >> at least to sedate your hearts. ;-)
> >> >
> >> > Functional programmers write obfuscated code, too. But unlike Perl,
> ^^^^^^^^^^
> >> > it still looks beautiful.
> >>
> >> Ok, what i learned now, is that perception of beautifulness could be
> >> very different.
> >
> > Well, in fact the code I posted is beautiful in a number of ways. It's
> > easy to read, very fast and also elegant. However, it is not beautiful
> ^^^^^^^^^^^^
>
> Code cannot be both "obfuscated" and "easy to read" at the same time.
> "Obfuscated" means hard to read (it can still be beautiful, though).
>
> [...]
>
> "Those Perl symbols" are part of the language syntax. So saying you
> need to understand those Perl symbols is the same as saying you just
> need to understand the language syntax.
That might be your definition of "obfuscated". Code can be hard to
understand, even if you happen to know all the language elements and
library functions it uses. My code example is of that kind.
Greets,
Ertugrul
--=20
nightmare =3D unsafePerformIO (getWrongWife >>=3D sex)
http://ertes.de/
------------------------------
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>
Administrivia:
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------------------------------
End of Perl-Users Digest V11 Issue 3169
***************************************
