[27108] in Perl-Users-Digest
Perl-Users Digest, Issue: 8985 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Wed Feb 22 21:05:42 2006
Date: Wed, 22 Feb 2006 18:05:05 -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 Wed, 22 Feb 2006 Volume: 10 Number: 8985
Today's topics:
Re: Alternate for buzzers in a competition (Raghuramaiah Gompa)
Re: DBD::CSV malfunction? xhoster@gmail.com
Error when trying to print to a file and locking <rbutcher.nospam@hotmail.com>
Re: Error when trying to print to a file and locking <1usa@llenroc.ude.invalid>
error-prone coding styles <samwyse@gmail.com>
Re: Reading Mac / Unix / DOS text files (Rick Scott)
Re: savely change permission and group on files <daleif@imf.au.dk>
Re: savely change permission and group on files <abigail@abigail.nl>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Thu, 23 Feb 2006 00:30:38 +0000 (UTC)
From: rgompa@steel.ucs.indiana.edu (Raghuramaiah Gompa)
Subject: Re: Alternate for buzzers in a competition
Message-Id: <dtivne$emd$1@rainier.uits.indiana.edu>
In article <Xns97717464CD60Eebohlmanomsdevcom@130.133.1.4>,
Eric Bohlman <ebohlman@omsdev.com> wrote:
>xhoster@gmail.com wrote in
>news:20060221093513.732$wa@newsreader.com:
>
>> rgompa@steel.ucs.indiana.edu (Raghuramaiah Gompa) wrote:
>>> We are hosting a math fair. We have teams competing.
>>> I am just wondering whether there is anyway we could use
>>> laptops to serve as buzzers. Laptops can be connected to
>>> a central computer through wireless. Team can press a
>>> button when they are ready. Can we write a perl code to
>>> do this on the computers? Please help. .. Raghu
>>
>> Yes. See IO::Socket::INET and IO::Select.
>
>That was my first thought too, but then I realized a
>simpler way would be
>just to set up an HTTP server on the central computer
>and run a CGI script
>that would deliver a very simple HTML form to each
>laptop and then record
>when each submit button was pressed. That way you
>don't need to write
>client software for the laptops.
Thank you so much for all suggestions. I will try to
answer some of
the questions posted about my post.
I am new to perl, but I am making progress. I have been
learning so much from this group. Thanks a lot.
I wanted to know whether perl code can be used to solve
the solving - I wanted to know such a code already exists
- I wanted to know whether it is feasible.
It seems using a webpage would be optimal. I would have
to read more to actually understand thoroughly. But this
gives me a direction to pursue. Thank you so much. ..
Raghu
------------------------------
Date: 23 Feb 2006 01:04:55 GMT
From: xhoster@gmail.com
Subject: Re: DBD::CSV malfunction?
Message-Id: <20060222200726.767$2A@newsreader.com>
Mark <Mark.Fenbers@noaa.gov> wrote:
> my $dbstr = 'DBI:CSV:f_dir=data';
> my $dbh = DBI->connect($dbstr,undef,undef,{ChopBlanks => 1,PrintWarn =>
> 1,PrintError => 0}) or warn "Cannot connect to: $dbstr: " .
> DBI->errstr;
You ask us for help without even asking DBI for help first? That is
insulting.
PrintError => 1
> my $sql = "SELECT * FROM location ORDER BY lid;";
valid SQL does not have a trailing ;
Xho
--
-------------------- http://NewsReader.Com/ --------------------
Usenet Newsgroup Service $9.95/Month 30GB
------------------------------
Date: Thu, 23 Feb 2006 00:20:32 GMT
From: "Robert" <rbutcher.nospam@hotmail.com>
Subject: Error when trying to print to a file and locking
Message-Id: <kd7Lf.61549$sa3.48710@pd7tw1no>
Hi,
I am getting the following error when trying to print to a file and locking.
Browser Error:
------------------
Bareword "LOCK_EX" not allowed while "strict subs" in use at record.pl line
208.
Execution of record.pl aborted due to compilation errors.
------------------
Here is my write-to-file code:
------------------
sub record {
my $nowtime = time();
my $newentry = "$nowtime|$invoice|$fullname|$company|$emailaddy|$phone";
open (LOCKER, "<lockfile.db") or die "Can't open file: $!";
flock (LOCKER, LOCK_EX) or die "Can't lock file: $!";
open (FH, ">>records.db") or die "Can't open file: $!";
print FH "$newentry\n";
close(FH);
close(LOCKER);
}
------------------
I always use "use strict;" in my programs and have never seen this error
before. I'm not sure where to start in researching a solution. Please if you
have any thoughts please and thank you.
Robert
------------------------------
Date: Thu, 23 Feb 2006 00:25:34 GMT
From: "A. Sinan Unur" <1usa@llenroc.ude.invalid>
Subject: Re: Error when trying to print to a file and locking
Message-Id: <Xns9772C5B692026asu1cornelledu@127.0.0.1>
"Robert" <rbutcher.nospam@hotmail.com> wrote in
news:kd7Lf.61549$sa3.48710@pd7tw1no:
> I am getting the following error when trying to print to a file and
> locking. Browser Error:
>
> ------------------
> Bareword "LOCK_EX" not allowed while "strict subs" in use at record.pl
> line 208.
> Execution of record.pl aborted due to compilation errors.
Hmmm ... Have you considered reading
perldoc -f flock
especially the part:
OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly
combined with LOCK_NB. These constants are traditionally valued
1, 2, 8 and 4, but you can use the symbolic names if you import
them from the Fcntl module, either individually, or as a group
using the ':flock' tag.
> ------------------
>
> Here is my write-to-file code:
>
> ------------------
> sub record {
>
> my $nowtime = time();
> my $newentry =
> "$nowtime|$invoice|$fullname|$company|$emailaddy|$phone";
>
> open (LOCKER, "<lockfile.db") or die "Can't open file: $!";
> flock (LOCKER, LOCK_EX) or die "Can't lock file: $!";
Have you considered reading:
perldoc -f flock
especially the part:
Note that the fcntl(2) emulation of flock(3) requires that
FILEHANDLE be open with read intent to use LOCK_SH and requires
that it be open with write intent to use LOCK_EX.
Sinan
--
A. Sinan Unur <1usa@llenroc.ude.invalid>
(reverse each component and remove .invalid for email address)
comp.lang.perl.misc guidelines on the WWW:
http://mail.augustmail.com/~tadmc/clpmisc/clpmisc_guidelines.html
------------------------------
Date: Thu, 23 Feb 2006 01:45:43 GMT
From: Samwyse <samwyse@gmail.com>
Subject: error-prone coding styles
Message-Id: <bt8Lf.36595$F_3.17459@newssvr29.news.prodigy.net>
Rick Scott wrote:
> (January Weiner <january.weiner@gmail.com> uttered:)
>
>>Rick Scott <rick@shadowspar.dyndns.org> wrote:
>>
>>>Given that it reduces the comprehensibility of your program and
>>>that you could have used any number of more legible identifiers,
>>>I'd call use of `IF' poor style, if not an outright error.
>>
>>Why an error? (yeah, it can lead to errors, agree, but then, of
>>course, a collegue of mine says the same about using Perl)
>
> Why cause a greater propensity to introduce errors than one has to?
One of the very first programs (non-Perl) that I had to maintain (as
opposed to create) was written by a joker who decided to use O as a
variable name. Distinguishing between
X = 0;
and
X = O;
was a source of much merriment for the rest of the staff. Fortunately
for his nose, he was quick at ducking whenever clenched fists were in
his vicinity.
------------------------------
Date: Thu, 23 Feb 2006 01:37:36 -0000
From: rick@shadowspar.dyndns.org (Rick Scott)
Subject: Re: Reading Mac / Unix / DOS text files
Message-Id: <1a69.43fd11e0.6c983@shadowspar>
(January Weiner <january.weiner@gmail.com> uttered:)
> Rick Scott <rick@shadowspar.dyndns.org> wrote:
> > Your filehandle `IF' collides with Perl's conditional `if' in
> > the mental hash-bucket of the programmers who have to read
> > your code.
>
> That's an argument. I will refrain from using <IF> in public. It
> causes too much stir and excites people.
>
> > Given that it reduces the comprehensibility of your program and
> > that you could have used any number of more legible identifiers,
> > I'd call use of `IF' poor style, if not an outright error.
>
> Why an error? (yeah, it can lead to errors, agree, but then, of
> course, a collegue of mine says the same about using Perl)
Why cause a greater propensity to introduce errors than one has to?
> > On the contrary -- I would posit that any coding practice that
> > makes it easier to inadvertently introduce bugs into your
> > program is a poor one. By using a bareword filehandle, you're
> > essentially using a package variable (*IF). If some other piece
> > of code in the same package namespace touches that bareword
> > while you're using it to read from a file, your filehandle will
> > get stomped and your code will break without you even having
> > changed it. That's why it's a bad idea.
>
> I think this depends a little on what you are using Perl for, and
> just some basic common sense is sufficient to say when using
> shorthand is OK and when it is a bad idea. I do use the <IF>
> construct in few-liners that do not read more than one file. I do
> think it is important to define variables if you are writing a
> larger piece of code. I do not understand the whole stir about
> this issue.
Since there's a way to do things that lets you do everything you can
do with a bareword filehandle without incurring the disadvantages,
why not make a habit of using it? As of Perl 5.6, you can do this:
open my $FILE, '<', $filename or die "Can't open file: $!";
Then the filehandle is stored in the lexical variable $FILE (where it
can't be stomped on by someone else's code) instead of in the package
variable *FILE (where it can).
> > Pick up a copy of Damian Conway's "Perl Best Practices" -- he
> > explains why this and about a thousand other `harmless style
> > preferences' aren't harmless, aren't stylish, and definitely
> > aren't preferable.
>
> So what is the problem with whitespace? Why is while(<STDIN>) more
> harmful than while ( <STDIN> ) ?
Actually, I'd go with the first of these two. About whitespace in
general -- there's not necessarily too many hard and fast rules;
you just want to make best use of it to increase the readability of
your code. To take an extreme example,
LINE:
foreach my $line (@lines) {
my ($registry, $cc, $type, $start, $length, $date, $status) =
split qr{\|}, $line;
next LINE unless $status;
next LINE unless ($type eq 'ipv4');
print $start;
}
is obviously much better than
LINE:foreach my $line(@lines){my($registry,$cc,$type,$start,$length,$date,$status)=split qr{\|},$line;next LINE unless $status;next LINE unless($type eq 'ipv4');print$start;}
or
LINE:
foreach
my
$line
(
@lines
)
{
my
($registry,
$cc,
$type,
$start,
$length,
$date,
$status)
=
split
qr{\|}
,
$line
;
...
or some other godawful thing.
Rick
--
key CF8F8A75 / print C5C1 F87D 5056 D2C0 D5CE D58F 970F 04D1 CF8F 8A75
Humankind cannot bear very much reality.
:Karen Armstrong
------------------------------
Date: Thu, 23 Feb 2006 01:14:50 +0100
From: Lars Madsen <daleif@imf.au.dk>
Subject: Re: savely change permission and group on files
Message-Id: <43fcfe5c$0$11674$ba624c82@nntp02.dk.telia.net>
> Huh? I don't get it. Why would you be vulnerable if you're doing something
> simple as changing the permissions of files?
>
if one (by mistake) runs sys commands on unchecked data
as in doing a naive delete of a file named '-rf /'
/daleif
------------------------------
Date: 23 Feb 2006 00:16:58 GMT
From: Abigail <abigail@abigail.nl>
Subject: Re: savely change permission and group on files
Message-Id: <slrndvpvnq.h1.abigail@alexandra.abigail.nl>
Lars Madsen (daleif@imf.au.dk) wrote on MMMMDLIX September MCMXCIII in
<URL:news:43fcfe5c$0$11674$ba624c82@nntp02.dk.telia.net>:
??
?? > Huh? I don't get it. Why would you be vulnerable if you're doing something
?? > simple as changing the permissions of files?
?? >
??
?? if one (by mistake) runs sys commands on unchecked data
If you are afraid you make mistakes like that, you shouldn't program
at all. There's no defence.
?? as in doing a naive delete of a file named '-rf /'
Huh? A native delete of a file in Perl is quite safe, and spelled 'unlink'.
Abigail
--
split // => '"';
${"@_"} = "/"; split // => eval join "+" => 1 .. 7;
*{"@_"} = sub {foreach (sort keys %_) {print "$_ $_{$_} "}};
%{"@_"} = %_ = (Just => another => Perl => Hacker); &{%{%_}};
------------------------------
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 8985
***************************************
