[30539] in Perl-Users-Digest
Perl-Users Digest, Issue: 1782 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Sat Aug 9 14:09:46 2008
Date: Sat, 9 Aug 2008 11:09:08 -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 Sat, 9 Aug 2008 Volume: 11 Number: 1782
Today's topics:
Re: CLPM - a help group? <tadmc@seesig.invalid>
Re: CLPM - a help group? <tadmc@seesig.invalid>
Re: CLPM - a help group? <rvtol+news@isolution.nl>
Re: Expression Parsing Help Needed <rvtol+news@isolution.nl>
Re: FAQ 4.70 How can I use a reference as a hash key? <ben@morrow.me.uk>
Re: FAQ 4.70 How can I use a reference as a hash key? <mjcarman@mchsi.com>
Re: FAQ 4.70 How can I use a reference as a hash key? <mjcarman@mchsi.com>
Re: FAQ 4.70 How can I use a reference as a hash key? <ben@morrow.me.uk>
Re: FAQ 4.70 How can I use a reference as a hash key? <mjcarman@mchsi.com>
Re: FAQ 4.70 How can I use a reference as a hash key? <ben@morrow.me.uk>
Re: FAQ 4.70 How can I use a reference as a hash key? <mjcarman@mchsi.com>
Re: How do I compare strings non-ascii-betically? <rvtol+news@isolution.nl>
Re: Need help with perlxs and C strings <sisyphus359@gmail.com>
Re: Newbie: Replacing double newlines <magloca@mailinater.com>
Re: Newbie: Replacing double newlines <nospam_here@videotron.ca>
Re: Trying to understand a constructor with an array. <tadmc@seesig.invalid>
Re: Trying to understand a constructor with an array. <tadmc@seesig.invalid>
Re: use/require, and variables (David Combs)
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Sat, 9 Aug 2008 07:30:31 -0500
From: Tad J McClellan <tadmc@seesig.invalid>
Subject: Re: CLPM - a help group?
Message-Id: <slrng9r3f7.od4.tadmc@tadmc30.sbcglobal.net>
Adam Worrall <worrall+unet@cs.bris.ac.uk> wrote:
> RedGrittyBrick wrote:
>> Adam Worrall wrote:
>>
>> <rant omitted>
>>
>> According to Google Groups you've made no contribution to this newsgroup
>> in the last decade. You now pop up and your only action is to start
>> telling regular contributors how they should be behaving.
>
> On the contrary, I did no such thing. I commented on my dislike for the
> regular contributors stance that they take that unless we do as _they_
> say, we are not part of the "community." And I have good reasons for
> leaving this news group years ago. People like you and the "regular
> contributors" make it very clear why many good people left this group.
You didn't like the newsgroup 10 years ago.
You do not like the newsgroup now.
We get it.
Effecting social change is pretty much impossible without having
some supporters of the changed position from within the society.
You have taken a pretty good shot at gaining a 2nd supporter of
your position, but I haven't seen one yet.
After a "sufficient" number of repetitions of the rationale for
a changed position, further repetition is increasingly unlikely
to change the outcome.
I would like to suggest that the number of repetitions in this
thread has reached a sufficient number.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: Sat, 9 Aug 2008 07:39:24 -0500
From: Tad J McClellan <tadmc@seesig.invalid>
Subject: Re: CLPM - a help group?
Message-Id: <slrng9r3vs.od4.tadmc@tadmc30.sbcglobal.net>
Adam Worrall <worrall+unet@cs.bris.ac.uk> wrote:
> I've seen more intelligent rebuttals from Paris Hilton
I like women with intelligent rebuttals.
That's hot!
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: Sat, 9 Aug 2008 18:08:34 +0200
From: "Dr.Ruud" <rvtol+news@isolution.nl>
Subject: Re: CLPM - a help group?
Message-Id: <g7kmi4.1j0.1@news.isolution.nl>
Adam Worrall schreef:
> How can a _volunteer_ service be _obligated_ to do anything? They are
> volunteers...
They will be sent away when they don't. You are not contributing so you
should really leave now.
*plonk*
--
Affijn, Ruud
"Gewoon is een tijger."
------------------------------
Date: Sat, 9 Aug 2008 18:30:20 +0200
From: "Dr.Ruud" <rvtol+news@isolution.nl>
Subject: Re: Expression Parsing Help Needed
Message-Id: <g7ko15.ao.1@news.isolution.nl>
Theresa schreef:
> Let’s say I have the following input strings:
>
> "ACCT Gold-P4 Mainframe - Germany Europe/Middle"
> "ACCT Gold-P1 Unix-AIX-Linux - France Europe/Middle"
> "ACCT Silver-P4 Database Infra Support client system - Germany Europe/
> Middle"
>
> [...] I need to grab:
> "Mainframe"
> "Unix-AIX-Linux"
> "Database Infra Support client system"
Both "\w+" in the code below are probably better written as
"[[:alpha:]]+".
#/usr/bin/perl
use strict;
use warnings;
while ( <DATA> ) {
m~^ACCT \w+-P[14] (.*) - \w+ \S+$~
and print $1, "\n";
}
__DATA__
ACCT Gold-P4 Mainframe - Germany Europe/Middle
ACCT Gold-P1 Unix-AIX-Linux - France Europe/Middle
--
Affijn, Ruud
"Gewoon is een tijger."
------------------------------
Date: Sat, 9 Aug 2008 10:32:59 +0100
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: FAQ 4.70 How can I use a reference as a hash key?
Message-Id: <br40n5-0f3.ln1@osiris.mauzo.dyndns.org>
Quoth PerlFAQ Server <brian@stonehenge.com>:
>
> 4.70: How can I use a reference as a hash key?
>
> (contributed by brian d foy)
>
> Hash keys are strings, so you can't really use a reference as the key.
> When you try to do that, perl turns the reference into its stringified
> form (for instance, "HASH(0xDEADBEEF)"). From there you can't get back
> the reference from the stringified form, at least without doing some
> extra work on your own. Also remember that hash keys must be unique, but
> two different variables can store the same reference (and those
> variables can change later).
I guess this last sentence is meant to cover the case where a variable
goes out of scope, and a different variable is then allocated at the
same address? Something more like
Also remember that the entry in the hash will not be removed when
the variable referenced goes out of scope, and that it is entirely
possible for perl to subsequently allocate a different variable at
the same address. This will mean a new variable might accidentally
be associated with the value for an old.
If you have perl 5.10 or later, and you just want to store a value
against the reference for lookup later, you can use the core
Hash::Util::Fieldhash module. This will also handle renaming the
keys if you use multiple threads (which causes all variables to be
reallocated at new addresses, changing their stringification), and
garbage-collecting the entries when the referenced variable goes out
of scope.
If you actually need to be able to get a real reference back from
each hash entry, you can use the Tie::RefHash module, which does the
required work for you.
might be better?
Ben
--
Like all men in Babylon I have been a proconsul; like all, a slave ... During
one lunar year, I have been declared invisible; I shrieked and was not heard,
I stole my bread and was not decapitated.
~ ben@morrow.me.uk ~ Jorge Luis Borges, 'The Babylon Lottery'
------------------------------
Date: Sat, 09 Aug 2008 13:04:09 GMT
From: Michael Carman <mjcarman@mchsi.com>
Subject: Re: FAQ 4.70 How can I use a reference as a hash key?
Message-Id: <dBgnk.290417$yE1.7165@attbi_s21>
Ben Morrow wrote:
> Quoth PerlFAQ Server <brian@stonehenge.com>:
>> 4.70: How can I use a reference as a hash key?
>>
>> Also remember that hash keys must be unique, but two different
>> variables can store the same reference (and those variables can
>> change later).
>
> I guess this last sentence is meant to cover the case where a
> variable goes out of scope, and a different variable is then
> allocated at the same address?
I don't think so. I think there are two parts to the caveat:
my @array;
my $ref1 = \@array;
my $ref2 = \@array;
my %hash = ($ref1 => 1, $ref2 => 2);
will result in a hash with only one key/value pair. And
$ref1 = [];
Would mean that $hash{$ref1} no longer returns the same value that it
used to.
Perl doesn't reuse memory allocated to lexical variables, so
reallocation (or accessing memory that's already been garbage collected)
should only be a potential problem for globals.
-mjc
------------------------------
Date: Sat, 09 Aug 2008 13:05:28 GMT
From: Michael Carman <mjcarman@mchsi.com>
Subject: Re: FAQ 4.70 How can I use a reference as a hash key?
Message-Id: <sCgnk.290421$yE1.85910@attbi_s21>
PerlFAQ Server wrote:
>
> Also remember that hash keys must be unique, but two different
> variables can store the same reference (and those variables can
> change later).
They don't survive freeze/thaw cycles through Storable, either. I
learned that one the hard way. ;)
-mjc
------------------------------
Date: Sat, 9 Aug 2008 14:33:29 +0100
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: FAQ 4.70 How can I use a reference as a hash key?
Message-Id: <9ui0n5-moc.ln1@osiris.mauzo.dyndns.org>
Quoth Michael Carman <mjcarman@mchsi.com>:
> Ben Morrow wrote:
> > Quoth PerlFAQ Server <brian@stonehenge.com>:
> >> 4.70: How can I use a reference as a hash key?
> >>
> >> Also remember that hash keys must be unique, but two different
> >> variables can store the same reference (and those variables can
> >> change later).
> >
> > I guess this last sentence is meant to cover the case where a
> > variable goes out of scope, and a different variable is then
> > allocated at the same address?
>
> I don't think so. I think there are two parts to the caveat:
>
> my @array;
> my $ref1 = \@array;
> my $ref2 = \@array;
> my %hash = ($ref1 => 1, $ref2 => 2);
>
> will result in a hash with only one key/value pair.
Well, yes; but this is no different from
my $key1 = 'foo';
my $key2 = 'foo';
my %hash = ($key1 => 1, $key2 => 1);
: it's not particular to using a ref as a key.
> And
>
> $ref1 = [];
>
> Would mean that $hash{$ref1} no longer returns the same value that it
> used to.
Again, no different from
my $key = 'foo';
my %hash = ($key => 1);
$key = 'bar';
# oh look, $hash{$key} isn't the same as it was before...
> Perl doesn't reuse memory allocated to lexical variables, so
> reallocation (or accessing memory that's already been garbage collected)
> should only be a potential problem for globals.
Obviously the details of this are system-dependant, but here I get
~% perl -le'sub foo { my $x; print \$x; } foo for 1..6'
SCALAR(0x8100c10)
SCALAR(0x810022c)
SCALAR(0x8100088)
SCALAR(0x8100c10)
SCALAR(0x810022c)
SCALAR(0x8100088)
so yes, perl does reuse lexicals once they've gone out of scope.
Ben
--
Every twenty-four hours about 34k children die from the effects of poverty.
Meanwhile, the latest estimate is that 2800 people died on 9/11, so it's like
that image, that ghastly, grey-billowing, double-barrelled fall, repeated
twelve times every day. Full of children. [Iain Banks] ben@morrow.me.uk
------------------------------
Date: Sat, 09 Aug 2008 15:02:46 GMT
From: Michael Carman <mjcarman@mchsi.com>
Subject: Re: FAQ 4.70 How can I use a reference as a hash key?
Message-Id: <qkink.290543$yE1.237955@attbi_s21>
Ben Morrow wrote:
> Quoth Michael Carman <mjcarman@mchsi.com>:
>>
>> my @array;
>> my $ref1 = \@array;
>> my $ref2 = \@array;
>> my %hash = ($ref1 => 1, $ref2 => 2);
>>
>> will result in a hash with only one key/value pair.
>
> Well, yes; but this is [...] not particular to using a ref as a key.
It isn't, but I think it's more likely to surprise unwary users.
>> Perl doesn't reuse memory allocated to lexical variables
>
> Obviously the details of this are system-dependant, but here I get
>
> ~% perl -le'sub foo { my $x; print \$x; } foo for 1..6'
> SCALAR(0x8100c10)
> SCALAR(0x810022c)
> SCALAR(0x8100088)
> SCALAR(0x8100c10)
> SCALAR(0x810022c)
> SCALAR(0x8100088)
>
> so yes, perl does reuse lexicals once they've gone out of scope.
Sorry, I should have been more specific. From perlfaq3:
Memory allocated to lexicals (i.e. my() variables) cannot be
reclaimed or reused even if they go out of scope. It is reserved
in case the variables come back into scope.
Your example re-enters the scope $x was declared in, so Perl will (can)
reuse the memory in that case. It would only do so if the refcount was
zero, of course. What perl *won't* do is reuse the memory in a different
scope.
-mjc
------------------------------
Date: Sat, 9 Aug 2008 16:54:40 +0100
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: FAQ 4.70 How can I use a reference as a hash key?
Message-Id: <07r0n5-h2j.ln1@osiris.mauzo.dyndns.org>
Quoth Michael Carman <mjcarman@mchsi.com>:
> Ben Morrow wrote:
> > Quoth Michael Carman <mjcarman@mchsi.com>:
> >>
> >> my @array;
> >> my $ref1 = \@array;
> >> my $ref2 = \@array;
> >> my %hash = ($ref1 => 1, $ref2 => 2);
> >>
> >> will result in a hash with only one key/value pair.
> >
> > Well, yes; but this is [...] not particular to using a ref as a key.
>
> It isn't, but I think it's more likely to surprise unwary users.
...OK, if you say so. I don't see why it should be, but maybe you're
right :).
> >> Perl doesn't reuse memory allocated to lexical variables
> >
> > Obviously the details of this are system-dependant, but here I get
<snip>
> > so yes, perl does reuse lexicals once they've gone out of scope.
>
> Sorry, I should have been more specific. From perlfaq3:
>
> Memory allocated to lexicals (i.e. my() variables) cannot be
> reclaimed or reused even if they go out of scope. It is reserved
> in case the variables come back into scope.
>
> Your example re-enters the scope $x was declared in, so Perl will (can)
> reuse the memory in that case. It would only do so if the refcount was
> zero, of course. What perl *won't* do is reuse the memory in a different
> scope.
This is true, but reentering a scope is hardly uncommon. For instance,
my %h;
for (1..4) {
my $x = [];
$h{$x} = 1;
}
will only leave one entry in %h, despite having created (and then
destroyed) four separate arrays.
Ben
--
You poor take courage, you rich take care:
The Earth was made a common treasury for everyone to share
All things in common, all people one.
'We come in peace'---the order came to cut them down. [ben@morrow.me.uk]
------------------------------
Date: Sat, 09 Aug 2008 17:22:57 GMT
From: Michael Carman <mjcarman@mchsi.com>
Subject: Re: FAQ 4.70 How can I use a reference as a hash key?
Message-Id: <Rnknk.236090$TT4.34025@attbi_s22>
Ben Morrow wrote:
> my %h;
> for (1..4) {
> my $x = [];
> $h{$x} = 1;
> }
>
> will only leave one entry in %h, despite having created (and then
> destroyed) four separate arrays.
Maybe we should just replace the entire FAQ answer with "Here be
dragons." :P
-mjc
------------------------------
Date: Sat, 9 Aug 2008 19:47:32 +0200
From: "Dr.Ruud" <rvtol+news@isolution.nl>
Subject: Re: How do I compare strings non-ascii-betically?
Message-Id: <g7kse5.ao.1@news.isolution.nl>
Suzanne schreef:
> I have to compare strings that are version numbers. I want to know if
> a version number is less than or equal to another version number.
$ echo "3.2.1.5" |perl -wple 's/(\d+)/sprintf "%03d", $1/ge'
003.002.001.005
Consider the "version" module as found in the CPAN:
http://search.cpan.org/~jpeacock/version-0.76/lib/version.pod
--
Affijn, Ruud
"Gewoon is een tijger."
------------------------------
Date: Sat, 9 Aug 2008 03:03:27 -0700 (PDT)
From: sisyphus <sisyphus359@gmail.com>
Subject: Re: Need help with perlxs and C strings
Message-Id: <4bbdd920-99d3-4fd6-ac54-d22d67f17f19@l33g2000pri.googlegroups.com>
On Aug 9, 12:49=A0am, Thomas <t...@example.invalid> wrote:
=2E
=2E
>
> =3D=3D runme.pl
> use Inline C =3D> Config =3D>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ENABLE =3D> AUTOWRAP =3D>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 LIBS =3D> "-L. -lsetdata";
The "-L." will be a problem as Inline's build directory (which is '.')
is almost certainly not the location that houses the setdata library.
So you'll need to replace that "-L." with the fully qualified location
of the setdata library -ie something like "-LC:/library/location".
And then, if it's not actually a 'setdata.lib' file, I doubt that the
'-lsetdata' will find it. Probably simplest to create a setdata.lib
from the setdata.obj file. With Visual Studio I think it's just a
matter of:
LIB /OUT:setdata.lib setdata.obj
Faik, it may even work if you rename setdata.a to setdata.obj (but I'm
a bit doubtful of that).
Cheers,
Rob
------------------------------
Date: Sat, 09 Aug 2008 13:01:36 +0200
From: magloca <magloca@mailinater.com>
Subject: Re: Newbie: Replacing double newlines
Message-Id: <489d7910$0$4243$6e1ede2f@read.cnntp.org>
Ben Morrow wrote:
> -0777 is equivalent to BEGIN { $/ = undef }: see perlrun.
Wow, that's obscure even for Perl. :D
m.
------------------------------
Date: Sat, 09 Aug 2008 07:01:17 -0400
From: Jensen <nospam_here@videotron.ca>
Subject: Re: Newbie: Replacing double newlines
Message-Id: <xOenk.6875$II.7327@weber.videotron.net>
Ben Morrow wrote:
> -p reads files line-by-line by default, so no one line will ever contain
> two newline characters. Try
>
> perl -0777 -pe 's/\n\n/ /g' test2
>
> -0777 is equivalent to BEGIN { $/ = undef }: see perlrun.
Thank you very much, that did it.
------------------------------
Date: Sat, 9 Aug 2008 08:42:20 -0500
From: Tad J McClellan <tadmc@seesig.invalid>
Subject: Re: Trying to understand a constructor with an array.
Message-Id: <slrng9r7ls.od4.tadmc@tadmc30.sbcglobal.net>
Overt <nowhere@nowhere.com> wrote:
>> I think what you want to do is:
>>
>> my $self = [ @{+shift} ];
>>
>
> Thank you. That fixed it.
[snip]
> I would not have discovered it on my own (at least for a long while),
> because I can't find that construction in any of my documentation. I am
> using Programming Perl, Perl Cookbook and Dan Conways Perl Object manual,
> plus about a dozen more (mostly useless) that I picked up on the discount
> bookshelf at Books-a-Million. Plus the PerlDocs on my system.
>
> Note that I say I can't find it - not that I say it isn't there.
(the resource you mentioned last above should be first, IMO.)
Not being able to find stuff in the std docs is an all too
common occurrence.
Write Perl daily for several years, and not being able to find
the (right) stuff in the std docs will still occur. :-)
I make a couple of "index files" from the std *.pod files
and then grep them.
You might like to review the "very new at perl programming"
thread rooted at:
http://groups.google.com/group/comp.lang.perl.misc/msg/c109a78448710b78
> Now the important questions.
> I am just a hobbyist programmer (so far), but where do you learn this type
> of info?
For a hobbyist, there are 2 different kinds of "this type of info",
and so there are 2 different approaches used depending on whether
it is a "general computer science" (1) or "language-specific" (2)
type of info that is being sought.
> I keep tripping across neat stuff like the above and wonder just
> how many zillions of other good items that I will never learn and can't
> use because I don't know they exist.
For the #2 type of info (especially when applied to Perl), get used to it.
Perl is chock-a-block full of interesting "corner cases", "special cases"
and "Do What I Mean" cases.
( but no "case statement"! :-)
Actually reading through the text of every Perl FAQ answer (and
following the references encountered) will probably cover the
20% of Perl that you will be using 80% of the time.
> Possibly you went to a professional
> school to learn.
That would be for #1 type of info.
So, how do people learn about general programming concepts as
well as learning language-specific things?
By "scratching an itch". That is, come up with a Perl programming
project that will be useful to you, then slough through whatever
it takes to get it implemented.
Then do it again.
Then do it again.
Then... you get the idea.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: Sat, 9 Aug 2008 09:01:07 -0500
From: Tad J McClellan <tadmc@seesig.invalid>
Subject: Re: Trying to understand a constructor with an array.
Message-Id: <slrng9r8p3.od4.tadmc@tadmc30.sbcglobal.net>
Michael Carman <mjcarman@mchsi.com> wrote:
> Overt wrote:
>>>
>>> my $self = [ @{+shift} ];
>>
>> I would not have discovered it on my own (at least for a long while),
>> because I can't find that construction in any of my documentation.
>
> That's probably because it's not one construct but several written together:
Nice list.
While perhaps not easy to find in the std docs, each is in there...
> * The [...] creates a reference to an anonymous array. This is what
> gets assigned to $self.
perldoc perlreftut
> * The @{...} is an array dereference.
errr,
perldoc perlreftut
again. :-)
> * The shift() function removes and returns the first element from an
> array. If no array is specified (and you're inside a subroutine) it
> operates on @_.
perldoc -f shift
> * @_ is the array used to pass arguments to subs.
perldoc perlsub
> * The + is the unary sign operator.
"Symbolic Unary Operators" section in:
perldoc perlop
And you'd never be expected to find it, but there is a relevant bit in:
perldoc -f print
where the 2 "usual" ways of disambiguating ambiguous syntax is mentioned:
interpose a C<+> or put parentheses around all the arguments
> It forces the "shift" to be
> interpreted as a function call instead of as a bareword. Without it
> the expression would parse as the array @shift instead of as
> @{ shift(@_) }
>
> Personally, I wouldn't write it this way, because I think it's very
> obscure. I would write
>
> my $self = shift;
I wouldn't write it either of those ways. I'd have written it:
my $self = [ @{ shift() } ];
That is, I universally choose the "put parens around arg list" way
rather than the "precede with a +" way.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: Sat, 9 Aug 2008 14:14:37 +0000 (UTC)
From: dkcombs@panix.com (David Combs)
Subject: Re: use/require, and variables
Message-Id: <g7k8od$6ul$1@reader1.panix.com>
I like this book you *never* see mentioned here:
Pro Perl, by Peter Wainwright, APRESS
1030pages, excellent, assumes, though, that you
already know how to program in some (any) language.
Cheap enough -- try www.bookpool.com, though amazon
has been lowering its prices a bit too.
Check out the amazon reviews.
David
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
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Subject: Digest Administrivia (Last modified: 6 Apr 01)
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------------------------------
End of Perl-Users Digest V11 Issue 1782
***************************************
