[31001] in Perl-Users-Digest
Perl-Users Digest, Issue: 2246 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Mar 3 11:09:44 2009
Date: Tue, 3 Mar 2009 08:09:11 -0800 (PST)
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, 3 Mar 2009 Volume: 11 Number: 2246
Today's topics:
Re: Net::SSH2 scp_put not working! <schaitan@gmail.com>
Re: Net::SSH2 scp_put not working! <schaitan@gmail.com>
Re: Net::SSH2 scp_put not working! <ben@morrow.me.uk>
Re: Net::SSH2 scp_put not working! <ben@morrow.me.uk>
Re: Net::SSH2 scp_put not working! (Gary E. Ansok)
Re: open for writing without immediately erasing <rvtol+usenet@xs4all.nl>
Re: perl dates: a notify alert window <unclebob@tnglwood.demon.co.uk>
Re: perl dates: a notify alert window <rvtol+usenet@xs4all.nl>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: variables that won't stay shared <cartercc@gmail.com>
Re: variables that won't stay shared <ben@morrow.me.uk>
What-if algorithm <gamo@telecable.es>
Re: What-if algorithm <sbryce@scottbryce.com>
Re: What-if algorithm <jurgenex@hotmail.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 3 Mar 2009 00:49:55 -0800 (PST)
From: Krishna Chaitanya <schaitan@gmail.com>
Subject: Re: Net::SSH2 scp_put not working!
Message-Id: <1242e656-b128-4256-a9c0-4064cd1a9cf4@a5g2000pre.googlegroups.com>
> The first problem I had was that my server doesn't allow 'password'
> auth, it requires 'keyboard' auth. The libssh2 documentation says this
> is quite common, so you may want to watch for it.
Thanks, I will.
> The second problem is here. It turns out that the ->READLINE and ->GETC
> methods on Net::SSH2::Channel require the session to be in non-blocking
> mode, but they don't set it themselves, and they don't handle timeouts
> properly. I would consider this a fairly serious bug in Net::SSH2.
I had the same feeling when I saw calls to poll in READLINE and GETC
(my assumption - it could be silly - is that poll is used in case of
non-blocking I/O), thanks for confirming. How could we attract the
module maintainer's attention w.r.t this?
>
> If your connection is fast enough that you can always guarantee to get a
> new character within 250ms of the last, you can set ->blocking(0) around
> all <> calls and it will stop hanging.
Sorry for being thick...can I verify this 250ms thing by checking
response time from a ping? Or is there another way for me?
>
> Also, you have a logic error here I hadn't noticed before. Had the <>
> been working properly, it would not have returned undef until the other
> end set end-of-file. Since the other end is a shell which is waiting for
> another command, that was never going to happen.
>
Hmm.....point taken. So should I instead be using a series of exec? Is
there no way to tell a shell to let me know it's done with the command
processing (some kind of a command-specific EOF)?
Thanks a lot, Ben.
------------------------------
Date: Tue, 3 Mar 2009 00:53:38 -0800 (PST)
From: Krishna Chaitanya <schaitan@gmail.com>
Subject: Re: Net::SSH2 scp_put not working!
Message-Id: <b20f91da-b69a-4643-982a-dbb2f9be2c2b@n33g2000pri.googlegroups.com>
>
> > Also, you have a logic error here I hadn't noticed before. Had the <>
> > been working properly, it would not have returned undef until the other
> > end set end-of-file. Since the other end is a shell which is waiting for
> > another command, that was never going to happen.
>
Also...how did <> manage to get EOF from shell in case of blocking
(0) .... ?
------------------------------
Date: Tue, 3 Mar 2009 09:58:10 +0000
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Net::SSH2 scp_put not working!
Message-Id: <iibv76-oo1.ln1@osiris.mauzo.dyndns.org>
Quoth Krishna Chaitanya <schaitan@gmail.com>:
>
> > The second problem is here. It turns out that the ->READLINE and ->GETC
> > methods on Net::SSH2::Channel require the session to be in non-blocking
> > mode, but they don't set it themselves, and they don't handle timeouts
> > properly. I would consider this a fairly serious bug in Net::SSH2.
>
> I had the same feeling when I saw calls to poll in READLINE and GETC
> (my assumption - it could be silly - is that poll is used in case of
> non-blocking I/O), thanks for confirming. How could we attract the
> module maintainer's attention w.r.t this?
It's usual for CPAN distributions to use rt.cpan.org for bugtracking, so
you could try sending mail to bug-Net-SSH2@rt.cpan.org. However, given
the list of untouched bugs in Net-SSH2's queue (see the 'View/Report
Bugs' link from search.cpan.org) I suspect the maintainer isn't reading
them.
> > If your connection is fast enough that you can always guarantee to get a
> > new character within 250ms of the last, you can set ->blocking(0) around
> > all <> calls and it will stop hanging.
>
> Sorry for being thick...can I verify this 250ms thing by checking
> response time from a ping? Or is there another way for me?
I don't think you can verify it at all. All you can really do is try
using readline when the network is loaded and see if it starts missing
lines.
> > Also, you have a logic error here I hadn't noticed before. Had the <>
> > been working properly, it would not have returned undef until the other
> > end set end-of-file. Since the other end is a shell which is waiting for
> > another command, that was never going to happen.
> >
>
> Hmm.....point taken. So should I instead be using a series of exec? Is
> there no way to tell a shell to let me know it's done with the command
> processing (some kind of a command-specific EOF)?
I would certainly have thought a series of exec would be easier, unless
you need the shell to keep state between commands. If you do you may
find it easier to ask for a pty, which means the shell will give you
prompts between commands, and use Expect.pm to drive it.
Ben
------------------------------
Date: Tue, 3 Mar 2009 09:59:02 +0000
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Net::SSH2 scp_put not working!
Message-Id: <6kbv76-oo1.ln1@osiris.mauzo.dyndns.org>
Quoth Krishna Chaitanya <schaitan@gmail.com>:
> >
> > > Also, you have a logic error here I hadn't noticed before. Had the <>
> > > been working properly, it would not have returned undef until the other
> > > end set end-of-file. Since the other end is a shell which is waiting for
> > > another command, that was never going to happen.
> >
>
> Also...how did <> manage to get EOF from shell in case of blocking
> (0) .... ?
It didn't. It was returning early with an error because the far end
hadn't sent another character for at least 250ms.
Ben
------------------------------
Date: Tue, 3 Mar 2009 15:09:13 +0000 (UTC)
From: ansok@alumni.caltech.edu (Gary E. Ansok)
Subject: Re: Net::SSH2 scp_put not working!
Message-Id: <gojh6p$22c$1@naig.caltech.edu>
In article <mfbt76-hn7.ln1@osiris.mauzo.dyndns.org>,
Ben Morrow <ben@morrow.me.uk> wrote:
>> print "Authorization successful\n";
>> my $chan2 = $ssh2->channel();
>> $chan2->shell();
>> $chan2->blocking(1);
>> print $chan2 "uname -a\n";
>> print "LINE : $_" while <$chan2>;
>
>The second problem is here. It turns out that the ->READLINE and ->GETC
>methods on Net::SSH2::Channel require the session to be in non-blocking
>mode, but they don't set it themselves, and they don't handle timeouts
>properly. I would consider this a fairly serious bug in Net::SSH2.
>
>If your connection is fast enough that you can always guarantee to get a
>new character within 250ms of the last, you can set ->blocking(0) around
>all <> calls and it will stop hanging. If a character is late, however,
>you will not only get an undef returned from <> when you shouldn't but
>you will lose the whole of the line that's been read so far. I would
>recommend dropping the tied filehandle interface and using ->read and
>->write instead, however that will make finding newlines considerably
>harder.
This is one reason I gave up on trying to use Net::SSH2 and went
back to Net::SSH::Perl instead. I was running a command that would
not return output quickly enough. With blocking in place, it never
returned. With blocking turned off, I couldn't reliably detect when
the remote command completed -- the readline returned undef any time
there was no output waiting to be read, and I couldn't get detection
of listener_closed or channel_closed to work reliably.
Net::SSH::Perl doesn't have the scp functions, but you may be able to
work around that. I use cat >file <<_END_OF_INPUT_ to create remote
files -- this could fail in the general case, of course, but the
set of files I needed to process was restricted enough that I knew
it would work for me.
Gary Ansok
--
Customer: "There are smoke and flames coming from my computer."
Tech Support: "Uh, hang up, unplug the computer from the wall,
and call the local fire department."
Customer: "No, I need to know how to do a backup. Fastest possible method."
------------------------------
Date: Tue, 03 Mar 2009 09:21:15 +0100
From: "Dr.Ruud" <rvtol+usenet@xs4all.nl>
Subject: Re: open for writing without immediately erasing
Message-Id: <49ace87b$0$188$e4fe514c@news.xs4all.nl>
mike wrote:
> is there a way to do 'open(FH, ">", x)' without erasing what's in the
> file? I want to open a file for writing then when I actually do the
> write, keep replacing just the first line (all that's ever in the file is
> a single line at the top) - but I don't want the (original) first line
> erased until I do my first new write.
>
> I tried ">>" and iterations of "seek(FH, -20, 0);" fiddling with
> position/whence but it seems (to me) that with ">>" perl treats the
> 'beginning' of the file as whatever position followed what existed in the
> file when it was opened; iow I can't go to absolute 0 in the file (or
> rather am having trouble figuring out how to go to 0).
Just don't open it until you need to write to it?
(or is the openness meant as a lock?)
--
Ruud
------------------------------
Date: Tue, 03 Mar 2009 08:18:47 +0000
From: Robert Billing <unclebob@tnglwood.demon.co.uk>
Subject: Re: perl dates: a notify alert window
Message-Id: <IJ5rl.42707$1N5.27880@newsfe21.ams2>
Eric wrote:
>> my $tm = localtime;
>> return ($tm->wday == 5 and $tm->hour > 17)
>> or ($tm->wday == 6)
>> or ($tm->wday == 0 and $hour < 17);
>>
>> if I wasn't going to use Date::Calc or DateTime.
>>
>> Ben
>
>
> Perl is a great language but there is no better support community than
> the perlers. A. Sinan, this is exactly the kind of elegance that I
It's only fair to point out that the minimal solution exists, but is far
too unreadable to be good practice.
( ( time() - $k1 ) % $k2 ) < $k3
where k1 is the number of seconds from the epoch to the first window, k2
is the number of seconds in a week and k3 is the size of the window.
However this depends on knowing the epoch, which is a Bad Thing, and
doing arithmetic with raw time() values which is a Worse Thing. This
version is really only good for winning obfuscation contests, you
wouldn't want it in the real world.
------------------------------
Date: Tue, 03 Mar 2009 09:18:59 +0100
From: "Dr.Ruud" <rvtol+usenet@xs4all.nl>
Subject: Re: perl dates: a notify alert window
Message-Id: <49ace7f3$0$188$e4fe514c@news.xs4all.nl>
cartercc wrote:
> Eric:
>> I'm having a little difficulty with this one. I want to have a notify
>> script "not" send messages during a weekend "quiet window" from Friday
>> 17:00 through Sunday 17:00. Sounds simple enough on the surface. I
>> just need an "okToSend()" function to return a True (1) if the
>> current date and time are not within that blackout window.
>
> localtime() returns both the hour and the weekday, like this:
>
> my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime
> (time);
> print qq(day is $wday and hour is $hour\n);
> my $quiet_window = 1;
> #default
> if ($wday == 5 and $hour > 17) { $quiet_window = 0; } #Friday night
> elsif ($wday == 6) { $quiet_window = 0; }
> #Saturday
> elsif ($wday == 0 and $hour < 17) { $quiet_window = 0; } #Sunday
> morning
> else { $quiet_window = 01 }
> #default again
ITYM: $wday == 5 and $hour > 16
--
Ruud
------------------------------
Date: Tue, 03 Mar 2009 08:17:55 GMT
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <TI5rl.11630$hc1.10288@flpi150.ffdc.sbc.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.noitatibaher\100cmdat/"
------------------------------
Date: Tue, 3 Mar 2009 07:00:47 -0800 (PST)
From: ccc31807 <cartercc@gmail.com>
Subject: Re: variables that won't stay shared
Message-Id: <2b1aff36-7aa9-4940-93c5-afcfca981fca@v15g2000yqn.googlegroups.com>
Thanks, Ben and Sinan. I've adopted the inline solution.
On Mar 2, 3:23=A0pm, Ben Morrow <b...@morrow.me.uk> wrote:
> Yes, it's absolutely significant. A cutdown version of your code with
> enough program round it to test it might look like:
Yes, I was too dense to see it, but I understand it now. My mind just
wasn't tracking with the diagnostics message.
> What exactly do you think is wrong with
>
> =A0 =A0 foreach my $key (
> =A0 =A0 =A0 =A0 sort {
> =A0 =A0 =A0 =A0 =A0 =A0 $calendarhash->{$a}{...} cmp $calendarhash->{$b}{=
...}
> =A0 =A0 =A0 =A0 } keys %{$calendarhash}
> =A0 =A0 ) {
>
There's nothing wrong with it. I usually like to use a style where I
place repeated code in named blocks that return values, IOW,
functions.
Thinking about this globally, I guess what I was thinking was that I
would use a private method in the module (I have two, one named
CONSOLE.pm and the other MUPD.pm). I know very little about OO Perl,
so my question would be if you can't use internal functions, how would
you write a private method in Perl? With Java, you can embed both
internal methods and internal classes, and in C++ you can use friend
functions as well as internal functions.
CC
------------------------------
Date: Tue, 3 Mar 2009 15:21:39 +0000
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: variables that won't stay shared
Message-Id: <3huv76-5j4.ln1@osiris.mauzo.dyndns.org>
Quoth ccc31807 <cartercc@gmail.com>:
> On Mar 2, 3:23 pm, Ben Morrow <b...@morrow.me.uk> wrote:
>
> > What exactly do you think is wrong with
> >
> > foreach my $key (
> > sort {
> > $calendarhash->{$a}{...} cmp $calendarhash->{$b}{...}
> > } keys %{$calendarhash}
> > ) {
> >
>
> There's nothing wrong with it. I usually like to use a style where I
> place repeated code in named blocks that return values, IOW,
> functions.
Yes, don't we all :). Are you saying you have the same sort block in
several places? If you really want to avoid anon subs, you could write a
sub that takes a hashref and does the whole sort:
sub sorted_calendar {
my ($cal) = @_;
return sort {
$cal->{$a}{...} cmp $cal->{$b}{...}
} keys %$cal;
}
and then just call that
foreach my $key (sorted_calendar $calendarhash) {
> Thinking about this globally, I guess what I was thinking was that I
> would use a private method in the module (I have two, one named
> CONSOLE.pm and the other MUPD.pm). I know very little about OO Perl,
> so my question would be if you can't use internal functions, how would
> you write a private method in Perl? With Java, you can embed both
> internal methods and internal classes, and in C++ you can use friend
> functions as well as internal functions.
Perl has a very minimal OO system, and one of the things it doesn't
provide natively is private methods. If you're learning Perl OO starting
now, and you are expecting it to look like other OO languages you've
come across, you may want to start out learning to use Moose rather than
the native OO. It's a little heavy, but it provides a very complete
object model similar to the one that will be in Perl 6.
Ben
------------------------------
Date: Tue, 3 Mar 2009 15:34:43 +0100
From: gamo <gamo@telecable.es>
Subject: What-if algorithm
Message-Id: <alpine.LNX.2.00.0903031527290.3460@jvz.es>
In excel you have a menu function that consist of given one
cell input and one cell output no matter how are related one
to other, you could search for the input that correspond to
a given value of the output.
That is, if I set $input and have a (complicated)
$output = f ( $input );
I can search in the reverse direction for a solution to
$output = XXX;
Do you know the subyacent algorithm or module to cover this?
TIA
--
http://www.telecable.es/personales/gamo/
"Was it a car or a cat I saw?"
perl -E 'say 111_111_111**2;'
------------------------------
Date: Tue, 03 Mar 2009 07:54:32 -0700
From: Scott Bryce <sbryce@scottbryce.com>
Subject: Re: What-if algorithm
Message-Id: <gojgbn$ffp$1@news.motzarella.org>
gamo wrote:
>
> In excel you have a menu function that consist of given one cell
> input and one cell output no matter how are related one to other, you
> could search for the input that correspond to a given value of the
> output.
>
> That is, if I set $input and have a (complicated) $output = f (
> $input ); I can search in the reverse direction for a solution to
> $output = XXX;
>
> Do you know the subyacent algorithm or module to cover this?
If I understand your question correctly, this will not always be
possible. There may be more than 1 input to the function that will give
a particular result.
3 = |x|
What is x? Do you want both solutions, or is there some way to specify
which solution is preferred?
------------------------------
Date: Tue, 03 Mar 2009 07:04:23 -0800
From: Jürgen Exner <jurgenex@hotmail.com>
Subject: Re: What-if algorithm
Message-Id: <dchqq496vd58ilm8cpjmle503uih1ba7s0@4ax.com>
gamo <gamo@telecable.es> wrote:
>
>
>In excel you have a menu function that consist of given one
>cell input and one cell output no matter how are related one
>to other, you could search for the input that correspond to
>a given value of the output.
>
>That is, if I set $input and have a (complicated)
>$output = f ( $input );
>I can search in the reverse direction for a solution to
>$output = XXX;
>
>Do you know the subyacent algorithm or module to cover this?
Because in the general case it is impossible to create the reverse
function f^-1 (it may not even exist) the only way is to enumerate and
loop over all $input values and compare the results to the desired
output value.
And you can do that with a simple grep():
@results = grep (f($_) == XXX, @candidates);
jue
jue
------------------------------
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