[19760] in Perl-Users-Digest
Perl-Users Digest, Issue: 1955 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Thu Oct 18 09:05:31 2001
Date: Thu, 18 Oct 2001 06:05:10 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Message-Id: <1003410310-v10-i1955@ruby.oce.orst.edu>
Content-Type: text
Perl-Users Digest Thu, 18 Oct 2001 Volume: 10 Number: 1955
Today's topics:
[OT] Flat file's auxiliary index (Mario Rizzuti)
Re: [OT] Flat file's auxiliary index <Thomas@Baetzler.de>
beginner: match a decimal number <Rene.Scheibe@gmx.net>
Re: beginner: match a decimal number <bernard.el-hagin@lido-tech.net>
Case-insensitive Command Line Args (Buck Turgidson)
Re: Checking a line of string <bernard.el-hagin@lido-tech.net>
Faster than split "\n", $txt; (Mario Rizzuti)
Re: Faster than split "\n", $txt; <Thomas@Baetzler.de>
Re: How to restore a filehandle tie correctly? <newspost@coppit.org>
Re: Matching & Merging two text files <lmoran@wtsg.com>
Re: NMAKE error while installing Net-SNMP package <tewilson@mitre.org>
Re: NMAKE error while installing SNMP module <tewilson@mitre.org>
Re: Perl->M$ SQL <bart.lateur@skynet.be>
Re: Perl->M$ SQL <bart.lateur@skynet.be>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@augustmail.com
Re: precedence question <weiss@kung.foo.at>
Re: precedence question <dtweed@acm.org>
Problem with output order <Chris@Clapham.org>
Re: Problem with output order <josef.moellers@fujitsu-siemens.com>
Re: Problem with output order <Thomas@Baetzler.de>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: 18 Oct 2001 04:17:18 -0700
From: mariorizzuti@yahoo.com (Mario Rizzuti)
Subject: [OT] Flat file's auxiliary index
Message-Id: <42f3ee2.0110180317.3e1a78ed@posting.google.com>
I am looking for an efficient way of building a flat file's index.
Various searches didn't return anything interesting.
The basic idea is to store a 4 bytes pointer (byte offset) for each
line then retrieving it with a
seek FH, $line * 4, 0;
read FH, $line_offset, 4;
The problem here is that, when a line in the main file changes its
length, all the offsets of the lines following need to be updated.
I am wondering if using the 4 bytes to store the line's length and
only once in a while having an absolute offset would be a good idea.
Something like this:
0.reclen
1.reclen
2.reclen
3.reclen
4.absolute
5.reclen
6.reclen
7.reclen
8.reclen
9.absolute
10.reclen
11.reclen
...
This way the read() is a little slower ( I read the nearest absolute
offset and add/subtract the reclens).
The update() is much faster ( update the record length and all the
absolute offsets next to the updated record).
A new problem is that if you add a record in the middle of the file or
delete a record, you mess up the absolute offsets locations.
Does anyone has a better idea?
---
Mario Rizzuti
------------------------------
Date: Thu, 18 Oct 2001 13:28:48 +0200
From: =?ISO-8859-1?Q?Thomas_B=E4tzler?= <Thomas@Baetzler.de>
Subject: Re: [OT] Flat file's auxiliary index
Message-Id: <v4ftstg67jk1sri29em6ad2qhod3skh2ss@4ax.com>
On 18 Oct 2001, mariorizzuti@yahoo.com (Mario Rizzuti) wrote:
>I am looking for an efficient way of building a flat file's index.
[...]
>Does anyone has a better idea?
Why invent the wheel again? use DB_File; - DB_RECNO might be what you're
looking for.
HTH,
--
use strict;my($i,$t,@r)=(0,'5 -.@BHJPT4acd6e2hk2lmn2o4r2s3tuz',map{ord}
split//,unpack('u*','L#`T&)QD5#0`#!!`#%1D)#08`#P05!!(3``$$"``#"0L&``('.
'"`P<!`````0$`'));$t=~s/(\d)(.)/$2x$1/eg;map{$t.=substr$t,$i,1,''while
$_--;$i++}@r;print"$t\n";# Thomas@Baetzler.de - http://baetzler.de/perl
------------------------------
Date: Thu, 18 Oct 2001 14:24:50 +0200
From: "Rene Scheibe" <Rene.Scheibe@gmx.net>
Subject: beginner: match a decimal number
Message-Id: <9qmhle$pavc5$1@ID-65612.news.dfncis.de>
I want to get the first decimal number of
the loadaverage but don't have success.
I do:
$number=`cat /proc/loadavg;
$number=~/(\d+\.\d*)/;
print $number;
but I always get all the numbers.
Please help.
(Read some docu but didn't really understood it.)
------------------------------
Date: 18 Oct 2001 12:30:08 GMT
From: Bernard El-Hagin <bernard.el-hagin@lido-tech.net>
Subject: Re: beginner: match a decimal number
Message-Id: <slrn9stidu.85e.bernard.el-hagin@gdndev25.lido-tech>
On Thu, 18 Oct 2001 14:24:50 +0200, Rene Scheibe <Rene.Scheibe@gmx.net> wrote:
> I want to get the first decimal number of
> the loadaverage but don't have success.
> I do:
> $number=`cat /proc/loadavg;
> $number=~/(\d+\.\d*)/;
> print $number;
> but I always get all the numbers.
Look at what you're doing. First, you set $number to the output
of the cat command (with a syntax error, but I won't tell). Next,
you're matching some stuff in $number and assigning it to the
special $1 variable. Finally, you're printing $number, which hasn't
changed since you first set it. Change:
print $number;
to:
print $1;
Cheers,
Bernard
------------------------------
Date: 18 Oct 2001 05:57:06 -0700
From: jc_va@hotmail.com (Buck Turgidson)
Subject: Case-insensitive Command Line Args
Message-Id: <f98999c8.0110180457.3353e00e@posting.google.com>
I adapted a version of grep I found somewhere, and got it working for
the most part, to my liking. However, I want to be able to enter
command line args such as "GREP -IL" in upper case, just in case I am
set to upper case. I tried adding the noted line, but it is ignored.
Can someone suggest what I should change? I am trying to avoid
putting lc() on each reference to $opt in the program.
#-------------------
# i ignore case
# c count only
# l list name only
# e regex
#-------------------
use Getopt::Std;
my %opt;
getopts('ivcle:',\%opt);
$opt = lc($opt); # <----- added this
my $pat = $opt{'e'} || shift;
my @args = splice(@ARGV,0);
my $previous_file = "";
foreach my $arg (@args) {
push(@ARGV,glob($arg));
}
my $mcount = 0;
while (<>) {
if (($opt{i})? /$pat/io : /$pat/o) {
$mcount++;
if ($ARGV ne $previous_file) {
print "File: $ARGV\n" unless ($opt{'c'} || $opt{'l'} ||
$opt{'v'});
}
$previous_file = $ARGV;
unless ($opt{'c'} || $opt{'l'} || $opt{'v'}) {
print "$_";
}
}
if (eof) {
if ($opt{'c'} && $mcount) {
printf("%5d $ARGV\n",$mcount);
} else {
if ($opt{'l'} && $mcount) {
print "$ARGV\n";
}
}
$mcount = 0;
$. = 0;
}
}
------------------------------
Date: 18 Oct 2001 10:22:01 GMT
From: Bernard El-Hagin <bernard.el-hagin@lido-tech.net>
Subject: Re: Checking a line of string
Message-Id: <slrn9statn.85e.bernard.el-hagin@gdndev25.lido-tech>
On Thu, 18 Oct 2001 11:57:23 +0200, Sasha <sasha_lui@yahoo.com> wrote:
> Hi
> I am writing a program which receives one line at a time. Each line may have
> some comment marked # or data containing name and phone number, I was
> wodering if some one could tell me how can I skips or ignore the data
> started or after # skips a line if it starts with # or skips a line with
> more than two words and save the lines data if it has two words.
>
> The data in a line looks like this
>
> # Here is an example of line data
>
> Peter 2131111111 # correct data it should be saved
>
> Andre 212112 333333 # Wrong data and it should be ignored
>
> Mark 212112 Angel # Wrong data and it should be ignored
>
>
>
> My program looks like :
>
>
>
> If (open (MYFILE, "data.dat")){
^^
That's a syntax error, but you're probably better off doing
the open this way:
open( MYFILE, 'data.dat' ) or die "Can't open 'data.dat': $!\n";
That way if the open fails you'll know why.
> $line = <MYFILE>;
>
> while ($line ne "") # Not end of file {
That's another syntax error. Besides that the comment is wrong
since that test only checks for an empty line, not the end of the
file. On top of that you're reading the file only once with:
$line = <MYFILE>;
But if you want to go through the whole file you have to do this in
the loop.
Try this:
while( defined( my $line = <MYFILE> ) ){
next unless $line =~ m/^\s*(\S+)\s*(\d+)\s*$/;
# do something with $1 - which is the name
# and $2 - which is the number
}
This assumes that nothing comes after the number in a line
with "correct" data.
Cheers,
Bernard
------------------------------
Date: 18 Oct 2001 03:50:35 -0700
From: mariorizzuti@yahoo.com (Mario Rizzuti)
Subject: Faster than split "\n", $txt;
Message-Id: <42f3ee2.0110180250.6a2ba849@posting.google.com>
What is the *fastest* way to split a string in lines?
---
Mario Rizzuti
------------------------------
Date: Thu, 18 Oct 2001 13:25:05 +0200
From: =?ISO-8859-1?Q?Thomas_B=E4tzler?= <Thomas@Baetzler.de>
Subject: Re: Faster than split "\n", $txt;
Message-Id: <7petstso13n5ed1ps4aos9ppean5d21c84@4ax.com>
On 18 Oct 2001, mariorizzuti@yahoo.com (Mario Rizzuti) wrote:
>What is the *fastest* way to split a string in lines?
use Benchmark; and figure out what's fastest for you. There is so much
playing into this (architecture, port, hardware) that one can't make a
valid general statement - it's always YMMV.
In your case, the most obvious speed gain would be to figure out if you
need to split the string into lines at all - but we can't help you with
that because you don't tell us what you're trying to do.
HTH,
--
use strict;my($i,$t,@r)=(0,'5 -.@BHJPT4acd6e2hk2lmn2o4r2s3tuz',map{ord}
split//,unpack('u*','L#`T&)QD5#0`#!!`#%1D)#08`#P05!!(3``$$"``#"0L&``('.
'"`P<!`````0$`'));$t=~s/(\d)(.)/$2x$1/eg;map{$t.=substr$t,$i,1,''while
$_--;$i++}@r;print"$t\n";# Thomas@Baetzler.de - http://baetzler.de/perl
------------------------------
Date: Thu, 18 Oct 2001 00:04:44 -0400
From: David Coppit <newspost@coppit.org>
Subject: Re: How to restore a filehandle tie correctly?
Message-Id: <3BCE54DC.8050804@coppit.org>
[snippage]
Benjamin Goldberg wrote:
>>The problem is that what I'm doing inside CGI::Cache to take into
>>account the previous tie isn't working correctly with FCGI. The code I
>>posted shows the essential problem.
>
> Hmm.
>
> In CGI::Cache's stop() function, you retie using:
>
> tie (*STDOUT,ref $OLD_STDOUT_TIE) if defined $OLD_STDOUT_TIE;
> tie (*STDERR,ref $OLD_STDERR_TIE) if defined $OLD_STDERR_TIE;
>
> This doesn't work for the simple reason that it creates a *new* tied
> object for the stream, which of course is not what's wanted in most
> cases.
Ah... Okay.
> In the post with which you start the thread, you try:
>
> # Doesn't work. Causes script to exit as soon as
> # FCGI::Stream::PRINT is called.
> #tie ( *STDOUT, $OLD_STDOUT_TIE ) if defined $OLD_STDOUT_TIE;
>
> This doesn't work for the obvious reason that $OLD_STDOUT_TIE isn't a
> class, it's an object. Oops :) Well, obvious when you compare it the
> code from start(), anyway :)
Oops. Typo. (Doesn't work anyway for the reason above.)
> The proper fix is to do this:
>
> tie( *STDOUT, "Tie::Restorer", $OLD_STDOUT_TIE )
> if defined $OLD_STDOUT_TIE;
>
> And create a package Tie::Restorer with the following contents:
> package Tie::Restorer;
> (*TIESCALAR, *TIEARRAY, *TIEHASH, *TIEHANDLE) =
> ( sub { $_[1] } ) x 4;
> 1;
Excellent! This is exactly what I needed. You get kudos in the changelog,
and a beer at the next Perl conference. :)
Regards,
David
------------------------------
Date: Thu, 18 Oct 2001 09:01:30 -0400
From: Lou Moran <lmoran@wtsg.com>
Subject: Re: Matching & Merging two text files
Message-Id: <7cktstcqr8ahf3qbf3v3cfhsafbfgk587n@4ax.com>
On Thu, 18 Oct 2001 06:06:35 -0400, Benjamin Goldberg
<goldbb2@earthlink.net> wrote wonderful things about sparkplugs:
[Snip]
>
>Text::CSV and Text::CSV_XS are good for reading and writing CSV files.
>
[Snip]
>
># note that if both tables have SSN, then that should
># be used as the primary key, not the person's name.
>merge( "table_one.csv", "Last Name, First Name" );
>merge( "table_two.csv", "Last Name, First Name" );
>
[Snip]
Wow! Thank you for an amzingly thorough answer. Unfortunately both
files DO NOT have the SSN. Thank you again.
--
TMTOWTDI: My way tends to be wrong...
lmoran@wtsg.com
------------------------------
Date: Thu, 18 Oct 2001 07:37:30 -0400
From: Thomas Wilson <tewilson@mitre.org>
Subject: Re: NMAKE error while installing Net-SNMP package
Message-Id: <3BCEBEFA.34D3F430@mitre.org>
Also, a good resource to have if you are going to be working with MAKE
files I suggest you purchase the book titled "Managing Projects with
Make" by Oram and Talbott. It is available from www.bookpool.com for
about $15.00 US.
Tony McIver wrote:
>
> I am trying to build the package for use on an WIN/2000 system so that
> I can use the Perl module SNMP.PM in Perl scripts. Everthing build ok
> using MS Visual C++. I did not build with the SSL support for SNMPv3.
> When I execute nmake I get the error "SNMP.xs(26) : fatal error C1083:
> Cannot open include file: 'unistd.h': No such file or directory"
------------------------------
Date: Thu, 18 Oct 2001 07:34:58 -0400
From: Thomas Wilson <tewilson@mitre.org>
Subject: Re: NMAKE error while installing SNMP module
Message-Id: <3BCEBE62.AAD17C15@mitre.org>
I suspect that you must first set the environment for using MSVC++
utilities by executing the file "vcvars32.bat" which if you do a search
will find under somewhere on your computer. Include the path to the
folder that contains the ".bat" file in your environment settings for
your computer so from the command line you do not have to navigate to
each time. Good luck.
Tony McIver wrote:
>
> I am trying to build the net-snmp-4.2.2 package for use on an WIN/2000
> system so that I can use the Perl module SNMP.PM in Perl scripts. Everything
> built using MS Visual C++ correctly. When I execute nmake I get the error
> "SNMP.xs(26) : fatal error C1083: Cannot open include file: 'unistd.h': No
> such file or directory" How do I solve this problem? Any help would be
> greatly appreciated.
>
> Thanks in advance,
>
> Tony McIver
------------------------------
Date: Thu, 18 Oct 2001 11:27:57 GMT
From: Bart Lateur <bart.lateur@skynet.be>
Subject: Re: Perl->M$ SQL
Message-Id: <r4ftst8hqcgrve1bfkj1rgbhbcdgnidgvp@4ax.com>
Jacqui caren wrote:
>while (($title,$child) = fetchrow_arrayref()) {
That ain't right. That fetchrow_arrayref method isn't attached to any
object.
--
Bart.
------------------------------
Date: Thu, 18 Oct 2001 11:30:24 GMT
From: Bart Lateur <bart.lateur@skynet.be>
Subject: Re: Perl->M$ SQL
Message-Id: <h6ftst85afag20n4aa8fskqs38p7cr4in1@4ax.com>
Benjamin Goldberg wrote:
>Your problem looks more like you're trying to do the equivilant of:
>
>while( my ($foo, $bar) = each %hash ) {
> while( my ($baz, $quux) = each %hash ) {
> ... stuff ...
> }
>}
>
>It's your code's fault, not the fault of ODBC.
It looks to me like what he wants to do, is traverse a tree stored in a
table. For each node, he wants to visit the children first, before
continuing with the next node. And no, I don't think SQL properly lends
itself to this. I'd simply turn the table into a tree in perl's memory,
and then traverse that.
--
Bart.
------------------------------
Date: Thu, 18 Oct 2001 12:43:14 GMT
From: tadmc@augustmail.com
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.2 $)
Message-Id: <C7Az7.1015192$ai2.76716449@bin2.nnrp.aus1.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: 1.2 $)
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.
This article describes things that you should, and should not, do to
increase your chances of getting an answer to your Perl question. It is
available in POD, HTML and plain text formats at:
http://mail.augustmail.com/~tadmc/clpmisc.shtml
For more information about netiquette in general, see the "Netiquette
Guidelines" at:
http://andrew2.andrew.cmu.edu/rfc/rfc1855.html
A note to newsgroup "regulars":
Please do not use the existence of these guidelines as a
"license to flame" or other meanness. It is possible that
a poster is not aware of the things discussed here. Let's
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" in the
very precise sense that they're used in technical conversation
(such as you're likely to 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 very unlikely that you're going to
get much benefit from using this group. We're not trying to boss
you around; we're just trying to convey the point without using
a lot 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 is expected regardless of what newsgroup
you are visiting. Lurking means to simply monitor a newsgroup for a
period of time until you become very familiar with local customs.
Think of a newsgroup as foreign culture. Each newsgroup has its own
specific customs and rituals. Get to know those customs and rituals
well before you participate. This will help you to 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.perl.com/CPAN-local/authors/Dean_Roehrich/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* the sections of quoted text
that your comments apply to. Failure to do this is called "Jeopardy"
posting because the answer comes before the question.
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://www.geocities.com/nnqweb/nquote.html
Speak Perl rather than English, when possible
Perl is much more precise than natural language. Saying it in Perl
instead will avoid misunderstanding your question or problem.
Do not say: I have variable with "foo\tbar" in it.
Instead say: I have $var = "foo\tbar", or I have $var = 'foo\tbar',
or I have $var = <DATA> (and show the data line).
Ask perl to help you
You can ask perl itself to help you find common programming mistakes
by doing two things: enable warnings (perldoc warnings) and enable
"strict"ures (perldoc strict).
You should not bother the hundreds/thousands of readers of the
newsgroup without first seeing if a machine can help you find your
problem. It is demeaning to be asked to do the work of a machine. It
will annoy the readers of your article.
You can look up any of the messages that perl might issue to find
out what the message means and how to resolve the potential mistake
(perldoc perldiag). If you would like perl to look them up for you,
you can put "use diagnostics;" near the top of your program.
Do not re-type Perl code
Use copy/paste or your editor's "import" function rather than
attempting to type in your code. If you make a typo you will get
followups about your typos instead of about the question you are
trying to get answered.
Provide enough information
If you do the things in this item, you will have an Extremely Good
chance of getting people to try and help you with your problem!
These features are a really big bonus toward your question winning
out over all of the other posts that you are competing with.
First make a short (less than 20-30 lines) and *complete* program
that illustrates the problem you are having. People should be able
to run your program by copy/pasting the code from your article. (You
will find that doing this step very often reveals your problem
directly. Leading to an answer much more quickly and reliably than
posting to Usenet.)
Describe *precisely* the input to your program. Also provide example
input data for your program. If you need to show file input, use the
__DATA__ token (perldata.pod) to provide the file contents inside of
your Perl program.
Show the output (including the verbatim text of any messages) of
your program.
Describe how you want the output to be different from what you are
getting.
If you have no idea at all of how to code up your situation, be sure
to at least describe the 2 things that you *do* know: input and
desired output.
Do not provide too much information
Do not just post your entire program for debugging. Most especially
do not post someone *else's* entire program.
Do not post binaries, HTML, or MIME
clpmisc is a text only newsgroup. If you have images or binaries
that explain your question, put them in a publically accessible
place (like a Web server) and provide a pointer to that location. If
you include code, cut and paste it directly in the message body.
Don't attach anything to the message. Don't post vcards or HTML.
Many people (and even some Usenet servers) will automatically filter
out such messages. Many people will not be able to easily read your
post. Plain text is something everyone can read.
Social faux pas to avoid
The first two below are symptoms of lots of FAQ asking here in clpmisc.
It happens so often that folks will assume that it is happening yet
again. If you have looked but not found, or found but didn't understand
the docs, say so in your article.
Asking a Frequently Asked Question
It should be understood that you may have missed the applicable FAQ
when you checked, which is not a big deal. But if the Frequently
Asked Question is worded similar to your question, folks will assume
that you did not look at all. Don't become indignant at pointers to
the FAQ, particularly if it solves your problem.
Asking a question easily answered by a cursory doc search
If folks think you have not even tried the obvious step of reading
the docs applicable to your problem, they are likely to become
annoyed.
If you are flamed for not checking when you *did* check, then just
shrug it off (and take the answer that you got).
Asking for emailed answers
Emailed answers benefit one person. Posted answers benefit the
entire community. If folks can take the time to answer your
question, then you can take the time to go get the answer in the
same place where you asked the question.
It is OK to ask for a *copy* of the answer to be emailed, but many
will ignore such requests anyway. If you munge your address, you
should never expect (or ask) to get email in response to a Usenet
post.
Ask the question here, get the answer here (maybe).
Beware of saying "doesn't work"
This is a "red flag" phrase. If you find yourself writing that,
pause and see if you can't describe what is not working without
saying "doesn't work". That is, describe how it is not what you
want.
Sending a "stealth" Cc copy
A "stealth Cc" is when you both email and post a reply without
indicating *in the body* that you are doing so.
Be extra cautious when you get upset
Count to ten before composing a followup when you are upset
This is recommended in all Usenet newsgroups. Here in clpmisc, most
flaming sub-threads are not about any feature of Perl at all! They
are most often for what was seen as a breach of netiquette. If you
have lurked for a bit, then you will know what is expected and won't
make such posts in the first place.
But if you get upset, wait a while before writing your followup. I
recommend waiting at least 30 minutes.
Count to ten after composing and before posting when you are upset
After you have written your followup, wait *another* 30 minutes
before committing yourself by posting it. You cannot take it back
once it has been said.
AUTHOR
Tad McClellan <tadmc@augustmail.com> and many others on the
comp.lang.perl.misc newsgroup.
------------------------------
Date: Thu, 18 Oct 2001 12:26:00 +0200
From: "Stefan Weiss" <weiss@kung.foo.at>
Subject: Re: precedence question
Message-Id: <1003400993.277113@newsmaster-04.atnet.at>
"Clinton A. Pierce" <clintp@geeksalad.org> wrote:
> [Note that "undefined" means that it's perfectly acceptable for the
> compiler to cause monkeys to come flying out of the programmer's butt
> playing Beethoven's 5th symphony on the banjo with their teeth.]
%whoops_undefined = (
c => "demons from programmer's nose",
perl => "monkeys from programmer's butt",
....
);
http://www.science.uva.nl/~mes/jargon/n/nasaldemons.html
Makes you wonder what a LISP interpreter would do...
CNR,
stefan
------------------------------
Date: Thu, 18 Oct 2001 12:33:58 GMT
From: Dave Tweed <dtweed@acm.org>
Subject: Re: precedence question
Message-Id: <3BCECAD5.A7477621@acm.org>
Martien Verbruggen wrote:
> You can't deduce perl's behaviour from how an 'equivalent' C program
> behaves.
I know. I was merely pointing out another example of how you can't
predict execution sequence from how you might think a parser works.
-- Dave Tweed
------------------------------
Date: Thu, 18 Oct 2001 13:37:46 +0100
From: Chris Hall <Chris@Clapham.org>
Subject: Problem with output order
Message-Id: <3BCECD1A.1090807@Clapham.org>
Hi,
I've got a bit on an annoying problem with a Perl prog I'm currently
writing. This is to be run by cron so I'd like a logfile to be kept, but
the snippet of code below always writes the stderr before stdout in said
logfile.
Piece of code:
8 open STDOUT, ">$LOGFILE" or die "Can't open the logfile\n";
9 open STDERR, ">&STDOUT" or die "Can't redirect STDERR\n";
10
11 print "Starting CD Backup utility at " . localtime() . "\n\n";
12
13 chdir($BKDIR) or die "Can't change to the backup directory\n";
14
15 opendir(THIS, ".") or die "Can't open directory '$BKDIR'";
16 unlink grep { !/^\.$/ && !/^\.\.$/ } readdir(THIS) or die "Failed
to delete some files from '$BKDIR'";
17 closedir(THIS);
Output in logfile:
Failed to delete some files from '/data/cdbkup/files' at ./bkup.pl line 16.
Starting CD Backup utility at Thu Oct 18 13:11:45 2001
Any ideas?
TIA
--
Chris.
------------------------------
Date: Thu, 18 Oct 2001 14:53:19 +0200
From: Josef =?iso-8859-1?Q?M=F6llers?= <josef.moellers@fujitsu-siemens.com>
Subject: Re: Problem with output order
Message-Id: <3BCED0BF.59E3CEF6@fujitsu-siemens.com>
Chris Hall wrote:
> =
> Hi,
> =
> I've got a bit on an annoying problem with a Perl prog I'm currently
> writing. This is to be run by cron so I'd like a logfile to be kept, bu=
t
> the snippet of code below always writes the stderr before stdout in sai=
d
> logfile.
You should set STDOUT to autoflush:
my $oldfh =3D select STDOUT; $|=3D1; select $oldfh;
-- =
Josef M=F6llers (Pinguinpfleger bei FSC)
If failure had no penalty success would not be a prize
-- T. Pratchett
------------------------------
Date: Thu, 18 Oct 2001 14:57:21 +0200
From: =?ISO-8859-1?Q?Thomas_B=E4tzler?= <Thomas@Baetzler.de>
Subject: Re: Problem with output order
Message-Id: <c3ktst8vv52mmtalf19up8fqgdev397jfl@4ax.com>
On Thu, 18 Oct 2001, Chris Hall <Chris@Clapham.org> wrote:
>I've got a bit on an annoying problem with a Perl prog I'm currently
>writing. This is to be run by cron so I'd like a logfile to be kept, but
>the snippet of code below always writes the stderr before stdout in said
>logfile.
You could try to unbuffer STDOUT by doing "$| = 1;".
But the big question is: Do you really need to merge STDIN and STDERR?
> 16 unlink grep { !/^\.$/ && !/^\.\.$/ } readdir(THIS) or die "Failed
>to delete some files from '$BKDIR'";
You could write:
unless( unlink grep { !/^\.$/ && !/^\.\.$/ } readdir(THIS) ){
print "Failed to delete bla bla bla: $!\n";
exit;
}
Just my $0.02,
--
use strict;my($i,$t,@r)=(0,'5 -.@BHJPT4acd6e2hk2lmn2o4r2s3tuz',map{ord}
split//,unpack('u*','L#`T&)QD5#0`#!!`#%1D)#08`#P05!!(3``$$"``#"0L&``('.
'"`P<!`````0$`'));$t=~s/(\d)(.)/$2x$1/eg;map{$t.=substr$t,$i,1,''while
$_--;$i++}@r;print"$t\n";# Thomas@Baetzler.de - http://baetzler.de/perl
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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------------------------------
End of Perl-Users Digest V10 Issue 1955
***************************************
