[31736] in Perl-Users-Digest
Perl-Users Digest, Issue: 2999 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Jun 22 14:09:23 2010
Date: Tue, 22 Jun 2010 11:09:06 -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, 22 Jun 2010 Volume: 11 Number: 2999
Today's topics:
Creating a makefile for installing a Perl application ( <news@lawshouse.org>
Re: DB_File (hash of array) problem <bart.lateur@telenet.be>
Re: DB_File (hash of array) problem <uri@StemSystems.com>
Re: DB_File (hash of array) problem <xhoster@gmail.com>
Fueling your car with natural gas from home <sustainable.future115@gmail.com>
Re: How to submit utility - not module - to CPAN <apeiron@isuckatdomains.net.invalid>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: Posting Guidelines for comp.lang.perl.misc ($Revisi <ralph@happydays.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 22 Jun 2010 14:12:02 +0100
From: Henry Law <news@lawshouse.org>
Subject: Creating a makefile for installing a Perl application (not a module)
Message-Id: <PIydnZ7SYpE-K73RnZ2dnUVZ8vSdnZ2d@giganews.com>
I have a medium-sized application written in Perl which I ship about
among a few friends. It has a couple of dozen of Perl programs and a
tree of about ten modules, plus some configuration files; there are also
OS-related files and shell scripts.
All these components need to be placed in the right libraries on
installation and I'm doing all that using "make", so that the user can
type "configure", "make" and then "make install". There are also "make
update" (to replace just the code) and "make uninstall".
Currently I have an entirely specific "configure" program (written in
Perl) which understands the details of the programs and modules and
where to put them, and which also understands the various system files
and how to install those too (entries in /etc/init.d for example). It
allows the user to change the default locations if required, and it also
makes a number of checks (libraries already exist, users are defined,
and the like).
I'd like to think, though, that there's a more general-purpose utility
somewhere, to which I could specify "this library's contents go there
unless the user says otherwise", and "the following users must be
defined on the system", and so on, which would then create the Makefile.
I've searched but I can't find anything at all on installing a Perl
_application_ (as distinct from installing Perl _modules_).
Where might I look?
--
Henry Law Manchester, England
------------------------------
Date: Tue, 22 Jun 2010 04:26:38 +0200
From: Bart Lateur <bart.lateur@telenet.be>
Subject: Re: DB_File (hash of array) problem
Message-Id: <un70265k5jpqjdrkm3or15u6s07lmgee1n@4ax.com>
James wrote:
>I am trying to write to a database a hash of array (as seen by
>__DATA__ in the code).
>But somehow the first element of the array is missing. Any idea why?
> for $i (0..$#v) {
> $h{$k}->[$i] = $r->[$i];
> }
Try a 1-based array for the DB.
for $i (0..$#v) {
$h{$k}->[$i+1] = $r->[$i];
}
>The second time, it is working correctly.
Now that is just plain weird.
--
Bart.
------------------------------
Date: Mon, 21 Jun 2010 23:44:01 -0400
From: "Uri Guttman" <uri@StemSystems.com>
Subject: Re: DB_File (hash of array) problem
Message-Id: <87k4prhgu6.fsf@quad.sysarch.com>
>>>>> "J" == James <hslee911@yahoo.com> writes:
J> I am trying to write to a database a hash of array (as seen by
J> __DATA__ in the code).
J> But somehow the first element of the array is missing. Any idea why?
J> The second time, it is working correctly.
as bart says, that is wierd. but your code is wierd too.
and what do you mean by first element of which array? you have several
instances of @v. all of them miss the first element? is this before or
after you write the hash? you need to be more specific about errors like
this.
J> $ cat run.pl
J> use DB_File;
J> use vars qw($db $x %h $k $v $i $key $val);
use vars is very old and mostly obsolete. lexicals are used now and you
should declare them when first used.
J> ($db) = @ARGV;
and what if @ARGV is empty? check for this. also your names are very
short and not informative. also below i remove several unneeded vars as
well.
my $db_name = shift @ARGV or die "must pass in a db name" ;
J> %h = ();
no need to assign () as hashes are always empty when declared or first
used.
J> $x = tie %h, "DB_File", $db, O_RDWR|O_CREAT, 0640, $DB_HASH;
you don't check that for an error either.
J> write_db();
you are using globals all over. sure, this is a short program but it is
a bad habit to get into.
J> read_db();
J> untie %h;
J> undef $x;
no need for those as they will be cleared upon program exit
J> sub write_db {
J> print "=== write $db ===\n";
ever heard of indenting code?
J> for (<DATA>)
it is poor style to use $_ as much as you do here. named vars are better
and safer too ($_ is a global and can be modified elsewhere).
J> {
J> ($k, @v) = split;
you know indenting. just oddly done.
my( $key, @values ) = split;
J> print "$k -> @v\n";
J> $r = \@v;
J> for $i (0..$#v) {
J> $h{$k}->[$i] = $r->[$i];
J> }
no need for any of that code:
$h{$k] = [@v] ;
that is all you did there. if @v were declare in the loop with my, then
you could just do:
$h{$k] = \@values ;
J> }
J> }
J> sub read_db {
J> print "=== read $db ===\n";
J> for ( $status = $x->seq($key, $val, R_FIRST); $status == 0; $status =
J> $x->seq($key, $val, R_NEXT) )
you tied the hash so why not use the hash interface, keys, values,
each. no one uses the db interface as it is noisy
while( my( $key, $val ) = each( %h ) {
isn't that a bit easier to read? tie is nice in allowing a cleaner hash
api vs some clunky db api.
also it might eliminate your bug. i don't know the dbfile api so i can't
tell why you have an off by one error only on the first run.
J> {
J> print "$key -> @{$val}\n";
J> }
J> $ ./run.pl mydb
J> === write mydb ===
J> aa -> 1 2 3
J> cc -> 678 99
J> zz -> foo fee fuu fun
J> === read mydb ===
J> aa -> 2 3
J> cc -> 99
J> zz -> fee fuu fun
and the second run works fine? show that output. does it still work if
you delete the dbfile between runs?
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.sysarch.com --
----- Perl Code Review , Architecture, Development, Training, Support ------
--------- Gourmet Hot Cocoa Mix ---- http://bestfriendscocoa.com ---------
------------------------------
Date: Mon, 21 Jun 2010 22:45:25 -0700
From: Xho Jingleheimerschmidt <xhoster@gmail.com>
Subject: Re: DB_File (hash of array) problem
Message-Id: <4c204feb$0$3994$ed362ca5@nr5-q3a.newsreader.com>
James wrote:
> I am trying to write to a database a hash of array (as seen by
> __DATA__ in the code).
> But somehow the first element of the array is missing. Any idea why?
I don't believe DB_File supports nested data structures.
> The second time, it is working correctly.
>
> $ cat run.pl
> use DB_File;
> use vars qw($db $x %h $k $v $i $key $val);
Ugg. Scope variables to the smallest scope you can.
You should use strict.
You seem to be accidentally using symbolic references.
The inner data never got stored in DB_File in the first place, it is
only stored in Perl's memory.
> for $i (0..$#v) {
> $h{$k}->[$i] = $r->[$i];
> }
The first time through, an array is auto-vivified, and it contains
$r->[0]. When a reference to this array is stuffed into $h{$k}, it gets
stringified to something like 'ARRAY(0x825c3dc)' because the tied hash
only accepts strings, not array references. At that point, the array
and the string become disconnected from each other, and the value of
that auto-vivified array, the copy of $r->[0], is lost.
The second subsequent time, you are using a symbol reference to a
variable with the peculiar name 'ARRAY(0x825c3dc)', into which you stuff
the remaining values.
> sub read_db {
> print "=== read $db ===\n";
> for ( $status = $x->seq($key, $val, R_FIRST); $status == 0; $status =
> $x->seq($key, $val, R_NEXT) )
> {
> print "$key -> @{$val}\n";
At this point, you are pulling the values out of the peculiarly named
variable using symbolic references.
If you separate your program so the perl instance that reads the DB is
not the same one that created it, you will find the values never got
stored to the DB in the first place.
Xho
------------------------------
Date: Tue, 22 Jun 2010 01:46:41 -0700 (PDT)
From: ".." <sustainable.future115@gmail.com>
Subject: Fueling your car with natural gas from home
Message-Id: <62868199-5a3d-49b1-9332-a51740f3f8ec@d8g2000yqf.googlegroups.com>
Dear Everyone,
as you know the price of the Oil is more and more increasing, while
the oil supply is decreasing. Moreover Oil is
causing wars, terror, oil spills, a lot of greenhouse gases. Do you
know that there is plenty of natural gas ? The
supply will last for many decades, probably for hundred years. A lot
of methane (natural gas) is found as shale gas,
a lot more will come from methane hidrates. Natural gas is causing
much less greenhouse gases and since it is found
locally, it will not cause any wars or terror. It will create jobs in
your own country and not in the middle east.
Do you know that by converting your car to natural gas, you can save a
lot of money ? It costs a lot lot less. You
may say that there are not enough gas stations, but you can fuel at
home* over night. You also should convert your
car to dual fuel, that means if your natural gas tank is empty you can
switch to petrol, until you find a gas station.
And the more people switch to natural gas, the more natural gas
stations will be built, otherwise they can not earn
money. Do you know that in Argentina there are almost 2 million CNG
(compressed natural gas vehicles), also in Pakistan
and Brazil there are more than 1,5 million CNG vehicles, whereas in
the US there are not even 200000 of them, although
most of the shale gas is found in the USA.
Sources:
http://www.usatoday.com/money/autos/2007-05-08-natural-gas-usat_N.htm
http://en.wikipedia.org/wiki/Natural_gas_vehicle
* http://www.tulsagastech.com/phill.html
------------------------------
Date: Tue, 22 Jun 2010 07:57:48 +0000 (UTC)
From: Chris Nehren <apeiron@isuckatdomains.net.invalid>
Subject: Re: How to submit utility - not module - to CPAN
Message-Id: <hvpqds$5oj$1@news.eternal-september.org>
On 2010-06-21, Steve Roscio scribbled these curious markings:
> G'day -
>
> I'd like to submit a small utility to CPAN (like those found in
> perlutil) It's not a module. How do I package it for upload?
The practice these days is to put it in the App:: namespace. See e.g.
ack and cpanm.
> Do I make a dummy module for it, holding just a shebang and the POD?
Modules don't have shebang lines.
--
Thanks and best regards,
Chris Nehren
Unless noted, all content I post is CC-BY-SA.
------------------------------
Date: Tue, 22 Jun 2010 02:15:02 -0500
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <duKdnVLxF89r_73RnZ2dnUVZ_iydnZ2d@giganews.com>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($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, 22 Jun 2010 11:17:38 -0400
From: Ralph Malph <ralph@happydays.com>
Subject: Re: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <c1b98$4c20d412$40779ac3$4115@news.eurofeeds.com>
tl, dnr
------------------------------
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:
To submit articles to comp.lang.perl.announce, send your article to
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Back issues are available via anonymous ftp from
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#For other requests pertaining to the digest, send mail to
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------------------------------
End of Perl-Users Digest V11 Issue 2999
***************************************
