[29873] in Perl-Users-Digest
Perl-Users Digest, Issue: 1116 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Fri Dec 14 06:09:57 2007
Date: Fri, 14 Dec 2007 03:09:21 -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 Fri, 14 Dec 2007 Volume: 11 Number: 1116
Today's topics:
A strange phenomena with Module Cwd <rwxrxrx@gmail.com>
Re: most elegant way to split text file randomly into n <jurgenex@hotmail.com>
Re: most elegant way to split text file randomly into n <krahnj@telus.net>
new CPAN modules on Fri Dec 14 2007 (Randal Schwartz)
Performance of CGI Reduced <visitprakashindia@gmail.com>
Re: Performance of CGI Reduced <c7eqjyg02@sneakemail.com>
Performance of the Reduced <visitprakashindia@gmail.com>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: Question about "undef'ing" variables <m@rtij.nl.invlalid>
Re: Question about "undef'ing" variables <klaus03@gmail.com>
Re: question..? <jurgenex@hotmail.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Fri, 14 Dec 2007 16:29:22 +0800
From: Scott <rwxrxrx@gmail.com>
Subject: A strange phenomena with Module Cwd
Message-Id: <fjtj9v$7tc$1@news.cn99.com>
[scott@FreeBSD ~/perl]$ cat cwd.pl
#!/usr/bin/perl
#
use Cwd;
$dir = getcwd();
print "$dir\n";
[scott@FreeBSD ~/perl]$ perl cwd.pl
/usr/home/scott/perl # How does this "/usr" prefix come?
[scott@FreeBSD ~/perl]$ pwd
/home/scott/perl
[scott@FreeBSD ~/perl]$
------------------------------
Date: Fri, 14 Dec 2007 05:27:48 GMT
From: "Jürgen Exner" <jurgenex@hotmail.com>
Subject: Re: most elegant way to split text file randomly into n parts?
Message-Id: <ovo8j.7672$sf.1996@trndny04>
Markus Dehmann wrote:
> What is the most elegant way to split a text file randomly into n
> parts? If the original file contains m lines, the n new file should
> each contain about m/n lines, chosen uniformly at random.
perldoc -q shuffle
and then simply write each chunk of m/n lines to an individual file.
jue
------------------------------
Date: Fri, 14 Dec 2007 06:47:01 GMT
From: "John W. Krahn" <krahnj@telus.net>
Subject: Re: most elegant way to split text file randomly into n parts?
Message-Id: <476226E2.CE47CBDE@telus.net>
Markus Dehmann wrote:
>
> What is the most elegant way to split a text file randomly into n
> parts? If the original file contains m lines, the n new file should
> each contain about m/n lines, chosen uniformly at random.
>
> Leaving the actual handling of files aside here is a naive solution:
>
> my $n = 10;
> foreach my $line (0..9999){
> my $r = rand;
> for(my $i=$n; $i>=0; --$i){
> if($r > $i/$n){
> print "Line $line: Print to file $i\n";
> last;
> }
> }
> }
>
> Are there other ways to do it? This seems like a very typical perl
> problem, so it would be interesting to see what solutions others come
> up with!
This may do what you want, or maybe not. :-)
my $n = 10;
while ( <FILE> ) {
my $i = 1 + $. % ( 1 + rand $n );
print "Line $.: Print to file $i\n";
}
John
--
use Perl;
program
fulfillment
------------------------------
Date: Fri, 14 Dec 2007 05:42:16 GMT
From: merlyn@stonehenge.com (Randal Schwartz)
Subject: new CPAN modules on Fri Dec 14 2007
Message-Id: <Jt0yIG.1wE5@zorch.sf-bay.org>
The following modules have recently been added to or updated in the
Comprehensive Perl Archive Network (CPAN). You can install them using the
instructions in the 'perlmodinstall' page included with your Perl
distribution.
Apache-AuthChecker-1.01
http://search.cpan.org/~swampfox/Apache-AuthChecker-1.01/
mod_perl based authentication module used to prevent brute force attacks via HTTP authorization.
----
Apache2-AuthenSecurID-0.5
http://search.cpan.org/~tobeya/Apache2-AuthenSecurID-0.5/
Authentication via a SecurID server
----
DBIx-DBSchema-0.36
http://search.cpan.org/~ivan/DBIx-DBSchema-0.36/
Database-independent schema objects
----
DBIx-FileSystem-1.7
http://search.cpan.org/~afrika/DBIx-FileSystem-1.7/
Manage tables like a filesystem
----
Date-Extract-0.01
http://search.cpan.org/~sartak/Date-Extract-0.01/
extract probable dates from strings
----
DateTime-Format-Natural-0.62_02
http://search.cpan.org/~schubiger/DateTime-Format-Natural-0.62_02/
Create machine readable date/time with natural parsing logic
----
Devel-PerlySense-0.0132
http://search.cpan.org/~johanl/Devel-PerlySense-0.0132/
IntelliSense for Perl
----
File-Rotate-Backup-0.13
http://search.cpan.org/~dowens/File-Rotate-Backup-0.13/
Make backups of multiple directories and rotate them on unix.
----
HTML-FormFu-0.02002
http://search.cpan.org/~cfranks/HTML-FormFu-0.02002/
HTML Form Creation, Rendering and Validation Framework
----
IO-Lambda-0.02
http://search.cpan.org/~karasik/IO-Lambda-0.02/
non-blocking I/O in lambda style
----
InSilicoSpectro-1.3.16
http://search.cpan.org/~alexmass/InSilicoSpectro-1.3.16/
Open source Perl library for proteomics
----
Keystone-Resolver-1.10
http://search.cpan.org/~mirk/Keystone-Resolver-1.10/
an OpenURL resolver
----
Konstrukt-0.5-beta12
http://search.cpan.org/~twittek/Konstrukt-0.5-beta12/
Web application/design framework
----
Konstrukt-0.5-beta13
http://search.cpan.org/~twittek/Konstrukt-0.5-beta13/
Web application/design framework
----
Mail-Box-IMAP4-SSL-0.02
http://search.cpan.org/~dagolden/Mail-Box-IMAP4-SSL-0.02/
handle IMAP4 folders with SSL
----
Math-GMPf-0.25
http://search.cpan.org/~sisyphus/Math-GMPf-0.25/
perl interface to the GMP library's floating point (mpf) functions.
----
Math-MPC-0.46
http://search.cpan.org/~sisyphus/Math-MPC-0.46/
perl interface to the MPC (multi precision complex) library.
----
Math-MPFR-2.02
http://search.cpan.org/~sisyphus/Math-MPFR-2.02/
perl interface to the MPFR (floating point) library.
----
Nagios-Plugin-0.22
http://search.cpan.org/~tonvoon/Nagios-Plugin-0.22/
A family of perl modules to streamline writing Nagios plugins
----
POE-Component-SSLify-0.10
http://search.cpan.org/~apocal/POE-Component-SSLify-0.10/
Makes using SSL in the world of POE easy!
----
POE-Component-Server-SimpleHTTP-1.27_01
http://search.cpan.org/~bingos/POE-Component-Server-SimpleHTTP-1.27_01/
Perl extension to serve HTTP requests in POE.
----
POE-Component-Server-SimpleHTTP-1.27_02
http://search.cpan.org/~bingos/POE-Component-Server-SimpleHTTP-1.27_02/
Perl extension to serve HTTP requests in POE.
----
POE-Component-Server-SimpleHTTP-1.27_03
http://search.cpan.org/~bingos/POE-Component-Server-SimpleHTTP-1.27_03/
Perl extension to serve HTTP requests in POE.
----
POE-Component-Server-SimpleHTTP-1.28
http://search.cpan.org/~bingos/POE-Component-Server-SimpleHTTP-1.28/
Perl extension to serve HTTP requests in POE.
----
Parse-Marpa-0.001_055
http://search.cpan.org/~jkegl/Parse-Marpa-0.001_055/
(pre-Alpha) Jay Earley's general parsing algorithm, with LR(0) precomputation
----
Rose-DB-0.737
http://search.cpan.org/~jsiracusa/Rose-DB-0.737/
A DBI wrapper and abstraction layer.
----
Rose-DB-Object-0.766
http://search.cpan.org/~jsiracusa/Rose-DB-Object-0.766/
Extensible, high performance RDBMS-OO mapper.
----
Rose-HTML-Objects-0.552
http://search.cpan.org/~jsiracusa/Rose-HTML-Objects-0.552/
Object-oriented interfaces for HTML.
----
Spreadsheet-Engine-0.03
http://search.cpan.org/~tmtm/Spreadsheet-Engine-0.03/
Core calculation engine for a spreadsheet
----
String-Clean-0.02
http://search.cpan.org/~notbenh/String-Clean-0.02/
use data objects to clean strings
----
Tie-Handle-TtyRec-0.02
http://search.cpan.org/~sartak/Tie-Handle-TtyRec-0.02/
write a ttyrec
----
WWW-MobileCarrierJP-0.05
http://search.cpan.org/~tokuhirom/WWW-MobileCarrierJP-0.05/
scrape mobile carrier information
If you're an author of one of these modules, please submit a detailed
announcement to comp.lang.perl.announce, and we'll pass it along.
This message was generated by a Perl program described in my Linux
Magazine column, which can be found on-line (along with more than
200 other freely available past column articles) at
http://www.stonehenge.com/merlyn/LinuxMag/col82.html
print "Just another Perl hacker," # the original
--
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<merlyn@stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
Perl/Unix/security consulting, Technical writing, Comedy, etc. etc.
See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training!
------------------------------
Date: Thu, 13 Dec 2007 21:28:54 -0800 (PST)
From: Praki <visitprakashindia@gmail.com>
Subject: Performance of CGI Reduced
Message-Id: <75990864-050b-4cf4-891b-29c8510a412e@i29g2000prf.googlegroups.com>
Hi All,
when i use
use CGI;
use CGI::Session;
use Net::LDAP;
in my cgi file the performance is reduced. i mean it takes more time
to get load every time and all the pages where ever i use this .
why it is happening ? is there any other alternative for this...
Thanks,
Prakash
------------------------------
Date: Thu, 13 Dec 2007 23:06:03 -0800 (PST)
From: Japhio <c7eqjyg02@sneakemail.com>
Subject: Re: Performance of CGI Reduced
Message-Id: <e7426eb5-33b0-4202-aaa1-4de00f7dcb35@i12g2000prf.googlegroups.com>
On Dec 14, 6:28 am, Praki <visitprakashin...@gmail.com> wrote:
> use CGI;
> use CGI::Session;
> use Net::LDAP;
>
> in my cgi file the performance is reduced. i mean it takes more time
> to get load every time and all the pages where ever i use this .
More time than what?
Using those modules means slurping several thousand lines of code into
your program, and yes, that takes some time.
> why it is happening ? is there any other alternative for this...
If you are using Apache, have a look at mod_perl http://perl.apache.org/,
which embeds a Perl interpreter in your webserver and caches the
compiled Perl code.
------------------------------
Date: Thu, 13 Dec 2007 21:26:07 -0800 (PST)
From: Praki <visitprakashindia@gmail.com>
Subject: Performance of the Reduced
Message-Id: <5665adb5-b9d6-4876-be55-30886c7b1fe8@i12g2000prf.googlegroups.com>
Hi All,
when i use
use CGI;
use CGI::Session;
use Net::LDAP;
in my cgi file the performance is reduced. i mean it takes more time
to get load every time and all the pages where ever i use this .
why it is happening ? is there any other alternative for this...
Thanks,
Prakash
------------------------------
Date: Fri, 14 Dec 2007 08:11:38 GMT
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.8 $)
Message-Id: <_Uq8j.53490$eY.50893@newssvr13.news.prodigy.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: 1.8 $)
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_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 and many others on the comp.lang.perl.misc newsgroup.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: Fri, 14 Dec 2007 08:35:20 +0100
From: Martijn Lievaart <m@rtij.nl.invlalid>
Subject: Re: Question about "undef'ing" variables
Message-Id: <pan.2007.12.14.07.35.20@rtij.nl.invlalid>
On Thu, 13 Dec 2007 22:40:23 -0500, somebody wrote:
> In the code snippet below, I process each line of a file using the split
> command. After the variables $a, $b, $c, and $d are used, I need to
Don't use $a and $b, they're magic. I understand this is just an example,
however, even in examples, don't use them.
> ensure they're "undef'd" before processing the next line, so the value
> assigned from the previous line is not defined. So the line ($a, $b,
> $c, $d) = (0) x 4; resets these variables. (In reality there are more
> variables). This seems to slow down my program significantly. Is there
Seems? Use a profiler to know for sure! I actually doubt it, programs
like this more often than not spend most of their time waiting on I/O and/
or doing (slow!) system calls. But you may be right.
> a better way to re-initialize these variables? Maybe define them local
> to the sub instead of globally?
Why make them global at all, if you have the option of making them local
to the sub? This is not about speed, but about maintainability.
> use vars qw($a $b $c $d);
>
> sub MySub
> {
> open(FILE,"<$myfile") or die "Can't open $myfile: $!";
> while ( <FILE> ) {
> chomp;
> @myline = split /\'/;
> #Need to undef these vars after each record.
> ($a, $b, $c, $d) = (0) x 4;
You don't undef them here, you set them to the number zero.
> Do stuff here with $a, $b, etc.
If you don't need them after the while loop has finished, make them local
to the while loop. If you do need them after the while loop has finished,
make them local to the sub.
Make these changes first, this is about good software engineering
practice. Remember, make it run right first, make it run fast after.
HTH,
M4
------------------------------
Date: Fri, 14 Dec 2007 02:21:57 -0800 (PST)
From: Klaus <klaus03@gmail.com>
Subject: Re: Question about "undef'ing" variables
Message-Id: <cb9d5f4d-6f00-4ade-87f3-93f98c81aabf@s12g2000prg.googlegroups.com>
On Dec 14, 4:40 am, somebody <s...@body.com> wrote:
> In the code snippet below, I process each line of a file using the split
> command. After the variables $a, $b, $c, and $d are used, I need to
> ensure they're "undef'd" before processing the next line, so the value
> assigned from the previous line is not defined. So the line
> ($a, $b, $c, $d) = (0) x 4; resets these variables.
It is common practice to reset your variables using "undef":
undef $a;
undef $b;
undef $c;
undef $d;
> [...] This seems to slow down my program significantly.
I would be suspicious about a simple line of code such as:
($a, $b, $c, $d) = (0) x 4;
slowing down your program significantly.
It seems to me that you are going in the wrong direction by trying to
prematurely optimize a single line of code where the real problem
could be something else: I suspect that you initialising more often
than you really have to. You might rethink your algorithm.
> [...] Maybe define them local to the sub instead
> of globally?
That's better practice in general and makes your code more
maintainable, but it should not make much difference as far as the
execution speed of your program is concerned.
However, having said all this, it occurs to me that the expression
"(0) x 4" is quite expensive, and if you simply follow the common
practice to use lexical instead of globals, you can then dispense with
constructing a complex expression such as "(0) x 4" alltogether.
The simple fact that you don't need to execute the complex instruction
"(0) x 4" could improve the execution speed, but again, using local
("lexical") variables instead of global ("package") variables in
itself should not make much difference as far as the execution speed
of your program is concerned.
======================
I also allowed myself to add some nitpicks to your code:
======================
> use vars qw($a $b $c $d);
could also be written as:
our ($a, $b, $c, $d);
but more importantly, it is better to avoid naming your variables "$a"
and "$b" alltogether (see perldoc -f sort) and choose a different
name, e.g. $aa, $bb.
> sub MySub
> {
>
> open(FILE,"<$myfile") or die "Can't open $myfile: $!";
open my $FILE, '<', $myfile or die "Can't open $myfile: $!";
> while ( <FILE> ) {
while ( <$FILE> ) {
>
> chomp;
>
> @myline = split /\'/;
@myline = split /'/;
-- Klaus
------------------------------
Date: Fri, 14 Dec 2007 05:34:54 GMT
From: "Jürgen Exner" <jurgenex@hotmail.com>
Subject: Re: question..?
Message-Id: <2Co8j.23604$Bg7.17406@trndny07>
malboros wrote:
> i just start learning Perl .... and i would like to know to know a
> free Perl editor !!!!
vi, emacs (in particular in Perl mode), ed, vim, ...
If you are on Windows then also Notepad, Wordpad, ... although those are
much less supportive.
Anyway, the FAQ has about a dozen or so suggestions, just see "perldoc -q
editor".
> easy to use ...
Which of course is very subjective. One man's trash is the other man's
treasure.
> thanks in advance !!!!!!
The exclamation mark and the dot on your keyboard are seriously stuck. You
may want to fix that.
jue
------------------------------
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