[32114] in Perl-Users-Digest
Perl-Users Digest, Issue: 3379 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue May 10 09:09:26 2011
Date: Tue, 10 May 2011 06:09:08 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Tue, 10 May 2011 Volume: 11 Number: 3379
Today's topics:
Re: fcntl/ $$ oddity sln@netherlands.com
Re: Moving data from one machine to another <RedGrittyBrick@spamweary.invalid>
Re: Moving data from one machine to another <justin.1104@purestblue.com>
Re: Moving data from one machine to another <peter@makholm.net>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: Sandboxing re sln@netherlands.com
Re: Sandboxing re sln@netherlands.com
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Mon, 09 May 2011 13:01:00 -0700
From: sln@netherlands.com
Subject: Re: fcntl/ $$ oddity
Message-Id: <q3hgs69csujumdvca8ns0h7rs1pvrhigju@4ax.com>
On Mon, 09 May 2011 15:40:33 +0100, Rainer Weikusat <rweikusat@mssgmbh.com> wrote:
>This text is supposed to document an oddity in the perl fcntl
>implementation which cropped up in a program I wrote as part of my job
>that puzzled me for a while.
>
>The mini perl script included below is supposed to tell the kernel
>that the current process is supposed to receive asynchronous I/O
>notification signals for the file descriptor belonging to the created
>socket.
>
>-------------------
>use Fcntl;
>use Socket;
>
>socket($sk, AF_UNIX, SOCK_STREAM, 0) or die("$!");
>print STDERR ("$$\n");
>fcntl($sk, F_SETOWN, $$) or die("$!");
>-------------------
>
>When trying to execute this on Debian 6.0.1/ perl 5.10.1, the
>fcntl-call aborts with the following error message:
>
>[rw@sapphire]/tmp $perl a.pl
>23000
>Modification of a read-only value attempted at a.pl line 6.
>
>The reason for this is that the print which preceded the fcntl caused
>the value of $$ to be stringified, meaning, it is now SvPOK. The error
>is actually caused (AFAIK) by the following code in pp_sys.c:
>
Fcntl is not implemented (I have ActiveState for windows installed) but apparently
I can duplicate your processing problem.
The docs for ioctl() state the SCALAR param, if a string state uses the address
to pass to fcntl(2). Otherwise it passes by value.
This may be independent of fnctl, more a Perl variable thing.
While this fails,
print STDERR ("$$\n");
fcntl($sk, LOCK_EX, $$) or die("$!");
with a "Modification of a read-only value attempted"
These all work:
print STDERR ("$$\n");
fcntl($sk, LOCK_EX, $$+0) or die("$!");
print STDERR ("$$\n");
fcntl($sk, LOCK_EX, \$$) or die("$!");
print STDERR $$,"\n";
fcntl($sk, LOCK_EX, $$) or die("$!");
Actually, the docs state if its a number, better to add a 0 to it to put
the variable into a numeric state.
The whole thing smells Perlish to me.
-sln
------------------------------
Date: Tue, 10 May 2011 11:28:49 +0100
From: RedGrittyBrick <RedGrittyBrick@spamweary.invalid>
Subject: Re: Moving data from one machine to another
Message-Id: <4dc91361$0$2501$db0fefd9@news.zen.co.uk>
On 05/05/2011 16:49, Justin C wrote:
> I have some SQL that extracts data from a database into a text file
> (it's run by a cron job), the text file is then emailed to another
> machine where the data will be used.
>
> I did look at running the SQL from the final destination machine so that
> I don't have to massage the data twice but I can't install the module
> required (DBD::Unify) without a 'working environment' - which is on the
> other machine.
>
> So I'm exporting the data to perl sticking it into a hash, exporting
> with Storable and emailing the file to another machine where procmail
> hands the file off to another perl program which, with Storable,
> retrieves the data... only it doesn't. If I print the exported data into
> the email I get 'Corrupted storable file', if I use nstore I get 'Byte
> order is not compatible at...'. And if I, instead, use MIME::Lite I
> don't seem to get the same file out the other end that I put in...
> probably down to MIME::Lite encoding the file - also, I'm not convinced
> that I can get procmail to just give me the attachment, and not the
> whole email.
>
> I've contemplated Net::SCP, but the two users are different and
> therefore the scp can't be done without authentication (no pre-shared
> keys being different users).
>
> This seems to be getting much more complicated than it need be, there
> must be [another|a better] way. Any suggestions how I might better do
> this? Am I over thinking this and I should just massage the data twice?
>
Using something like SOAP::Lite might simplify the problem. Have the
consumer of the data request it from the provider of the data.
--
RGB
------------------------------
Date: Tue, 10 May 2011 11:08:09 +0100
From: Justin C <justin.1104@purestblue.com>
Subject: Re: Moving data from one machine to another
Message-Id: <9dfn98-s6m.ln1@zem.masonsmusic.co.uk>
On 2011-05-05, John Bokma <john@castleamber.com> wrote:
> Justin C <justin.1104@purestblue.com> writes:
>
>> I have some SQL that extracts data from a database into a text file
>> (it's run by a cron job), the text file is then emailed to another
>> machine where the data will be used.
>>
>> I did look at running the SQL from the final destination machine so that
>> I don't have to massage the data twice but I can't install the module
>> required (DBD::Unify) without a 'working environment' - which is on the
>> other machine.
>
> You mean a compiler?
No, I mean a Unify database install/working environment.
>> So I'm exporting the data to perl sticking it into a hash, exporting
>> with Storable and emailing the file to another machine where procmail
>> hands the file off to another perl program which, with Storable,
>> retrieves the data... only it doesn't. If I print the exported data into
>> the email I get 'Corrupted storable file', if I use nstore I get 'Byte
>> order is not compatible at...'. And if I, instead, use MIME::Lite I
>> don't seem to get the same file out the other end that I put in...
>> probably down to MIME::Lite encoding the file - also, I'm not convinced
>> that I can get procmail to just give me the attachment, and not the
>> whole email.
>
> Why on Earth are you using Storable?
For it's "persistence of Perl data structures" and it's ability to
"allow easy sharing across multiple platforms."
> It's a text file... I would say:
> gzip the data and email that, and then do the post-processing on the
> other machine.
If I send over just the text I can't do
use Storable;
my $hashref = retrieve('somefile');
Which means I've got to take much more care over getting the data into
the program on the receiving machine.
> If you want to "massage" the data on-site, why not store
> it using JSON or YAML? It sounds like most of it is text data. You can
> always compress the JSON/YAML output using gzip.
Aren't those two just another way to do the same thing, but requiring
more code/effort on my part?
I don't see a way that using either would be quicker/easier than:
use Storable;
store \%parts_info, 'parts_info';
> MIME::Lite shouldn't be a problem. How do you decode the email on the
> other side?
procmail is piping it ... though, I think I need to decode the MIME
first... Which I'm not having a lot of luck with, according to the MUA
the attachment is there, it's the right size, but MIME::Parser doesn't
seem to be getting hold of it, requires further investigation.
Justin.
--
Justin C, by the sea.
------------------------------
Date: Tue, 10 May 2011 14:12:16 +0200
From: Peter Makholm <peter@makholm.net>
Subject: Re: Moving data from one machine to another
Message-Id: <87sjsmg3fj.fsf@vps1.hacking.dk>
Justin C <justin.1104@purestblue.com> writes:
>> Why on Earth are you using Storable?
>
> For it's "persistence of Perl data structures" and it's ability to
> "allow easy sharing across multiple platforms."
[...]
> I don't see a way that using either would be quicker/easier than:
> use Storable;
> store \%parts_info, 'parts_info';
This is not portable across multiple platforms. It doesn't work acress
different endianness. It doesn't work across different installed
versions of Storable. And I don't think it works across different word
lengths (32bit/64bit).
Using nstore solves the first problem, but the other two remains.
In most cases I would recommend JSON::XS which doesn't require more code
when used with the procedural interface:
use JSON::XS;
$datablob = encode_json \%parts;
No need to write it to a file when you are going to send it in an email.
The main reasons for not using JSON::XS is (IMHO)
- Need to store cyclic structures
- Need to store Regexp objects
Neither module supports CODE refs or dualvar values.
//Makholm
------------------------------
Date: Tue, 10 May 2011 02:14:35 -0500
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <eOqdnZurPZdGeFXQnZ2dnUVZ5sednZ2d@giganews.com>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
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AUTHOR
Tad McClellan and many others on the comp.lang.perl.misc newsgroup.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.
------------------------------
Date: Mon, 09 May 2011 13:45:56 -0700
From: sln@netherlands.com
Subject: Re: Sandboxing re
Message-Id: <j3jgs6dh5kdo0ungrqbo37d0n7qft970m6@4ax.com>
On Wed, 04 May 2011 15:41:27 -0500, John Bokma <john@castleamber.com> wrote:
>
>I want to be able to allow users to enter regular expressions. Since
>Perl's default re are way too powerful (code execution), is there some
>way to sandbox or limit the the capabilities?
>
>I just looked at POSIX::Regexp but it gives a segmentation fault here
>(oops, will look futher into it & bug report).
>
>I've noticed that there are several re::engine modules, maybe the Plan9
>one is sufficient for my needs.
>
>Any tips are welcome, thanks.
You probably want to allow user regex's in a limited way, interacting in
a certain context.
On-line regex testers are a good example.
Some pitfalls:
- How do you trap runtime errors or code execution?
- Is it query only, or will you allow data modification?
- What modifiers will you allow?
I could be wrong but, I think that eval BLOCK, used as a trap might work.
For instance,
print "enter regex: ";
chomp (my $rx = <STDIN>);
eval {
no warnings 'all';
if ("abcdefg12345" =~ /($rx)/x) {
print "found $1\n----------------\n";
}
};
warn "== $@" if $@;
will trap runtime syntax errors as well as code
execution in either (?{}) or (?{{}})
-sln
------------------------------
Date: Mon, 09 May 2011 14:02:08 -0700
From: sln@netherlands.com
Subject: Re: Sandboxing re
Message-Id: <glkgs6drdt7ei2a47r3mcvluualo1n3pa6@4ax.com>
On Mon, 09 May 2011 13:45:56 -0700, sln@netherlands.com wrote:
>I could be wrong but, I think that eval BLOCK, used as a trap might work.
>
>For instance,
>
> print "enter regex: ";
> chomp (my $rx = <STDIN>);
>
> eval {
> no warnings 'all';
> if ("abcdefg12345" =~ /($rx)/x) {
^^^
To clarify, if this regex were
/(?{print $local_var })/x) {
no "Eval-group not allowed at runtime" error would be emitted.
That is because this regex apparently is not compiled at runtime.
If it contains a variable in the regex like
/$runtime_var (?{print $local_var })/x
that contains external code,
where $runtime_var = '(?{code execution})';
a fault will be generated unless use re 'eval';
exists in the program.
This is my understanding anyway.
-sln
------------------------------
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------------------------------
End of Perl-Users Digest V11 Issue 3379
***************************************
