[30208] in Perl-Users-Digest
Perl-Users Digest, Issue: 1451 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Apr 15 16:35:53 2008
Date: Tue, 15 Apr 2008 13:35:43 -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, 15 Apr 2008 Volume: 11 Number: 1451
Today's topics:
Re: perl should be improved and perl6 <m@rtij.nl.invlalid>
Re: Time::HiRes < 1.91 and glibc 2.4 incompatibility <m@rtij.nl.invlalid>
Accessing a hash whose name is constructed <roblund@gmail.com>
Re: Accessing a hash whose name is constructed xhoster@gmail.com
Re: Accessing a hash whose name is constructed <jurgenex@hotmail.com>
How to know if data is piped into my script <asolkar@gmail.com>
Re: How to know if data is piped into my script xhoster@gmail.com
Re: How to know if data is piped into my script <devnull4711@web.de>
Re: Print a separator between each iteration of a forea xhoster@gmail.com
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 15 Apr 2008 21:12:03 +0200
From: Martijn Lievaart <m@rtij.nl.invlalid>
Subject: Re: perl should be improved and perl6
Message-Id: <pan.2008.04.15.19.12.02@rtij.nl.invlalid>
On Sat, 12 Apr 2008 14:02:59 -0700, Gordon Etly wrote:
> RedGrittyBrick wrote:
>> Gordon Etly wrote:
>>> RedGrittyBrick wrote:
>>>> Gordon Etly wrote:
>>>>> RedGrittyBrick wrote:
>>>>>> Gordon Etly wrote:
>>>>>>> Sherman Pendley wrote:
>>>>>>>> "Gordon Etly" <get@bentsys.com> writes:
>>>>>>>>
>>>>>>>> ... endlessly ...
>>>>>>>>
>>>>>>>> Will you give it a bloody rest already? Larry Wall invented the
>>>>>>>> language, and he says it's not called PERL. His language, his
>>>>>>>> call.
>>>>>>> Wrong, Larry himeself described it the same way 'perldoc perl'
>>>>>>> does.
>>>>>> i.e. both Larry and the docs use "perl" or "Perl" but *never*
>>>>>> "PERL" and have done so for many years.
>>>>>>
>>>>>>
>>>>>>
>>>>>> See this page and the articles under "Culture".
>>>>>> http://www.wall.org/~larry/perl.html
>>>>>>
>>>>>> No mentions of PERL that I can see.
>>>>> 'perldoc perl' defines PERL as "Practical Extraction and Report
>>>>> Language" in the NAME line. Why do you ignore this?
>>>>>
>>>> 'perldoc perl' defines perl as "Practical Extraction and Report
>>>> Language" in the NAME line. I'm not ignoring that.
>>>>
>>>> 'perldoc perl' contains "Perl" hundreds of times and 'PERL' zero
>>>> times. Why do you ignore this?
>>>
>>> I'm not ignoring it at all. Whether or not "PERL" is used throughout
>>> the documentation isn't the issue here.
>>
>> I believe it is germane to the issue.
>
> Sorry, but no, that was never the issuer at hand, but rather a tangent
> off the issue.
>
>>> What is the issue is the fact that
>>> since the main document defines "Practical Extraction and Report
>>> Language", it should //not// be //wrong// to use "PERL".
>>
>> I think it is your opinion, not a "fact", that your conclusion flows
>> from your premise.
>
> 'perldoc perl' is not my opinion.
>
> It states "Practical Extraction and Report Language" and therefore I
> don't know why it should be considered wrong to use "PERL" as a short
> for that, which it very well is.
>
> [...]
Well if you just snip the arguments without addressing them, I guess
there is no arguing possible.
M4
------------------------------
Date: Tue, 15 Apr 2008 20:58:11 +0200
From: Martijn Lievaart <m@rtij.nl.invlalid>
Subject: Re: Time::HiRes < 1.91 and glibc 2.4 incompatibility
Message-Id: <pan.2008.04.15.18.58.10@rtij.nl.invlalid>
On Tue, 15 Apr 2008 12:07:33 -0400, Mark Seger wrote:
>> The useconds_t type is only defined to support values up to 1,000,000.
>> Depending on undefined behavior is a mistake on the caller's part. The
>> AIX C library also returns an error if values >1M are passed in; it's
>> not a glibc bug.
>> ualarm is replaced by setitimer, which has seconds and microseconds.
>> --S
>
> I've been thinking about this some more, and I guess the question in my
> mind is how did this ever work? pre HiRes .91, ularm of 10 seconds
> works with glibc 2.3 and doesn't work with glibc 2.4.
If something is defined only when <condition> holds it is not defined
that it will not work <condition> doesn't hold. It might even work in
case condition is not satisfied! But depending on that undefined
behaviour might break in the next release, as was most probably the case
here.
M4
------------------------------
Date: Tue, 15 Apr 2008 12:46:49 -0700 (PDT)
From: Gibbering <roblund@gmail.com>
Subject: Accessing a hash whose name is constructed
Message-Id: <8de82ba9-9ba8-48aa-be17-549ad79f6e00@q24g2000prf.googlegroups.com>
I want to access some data from a hash, but want to build that hash's
name on the fly... here's the code:
%hello = (a => 'doggy');
print ${'hell' . lc 'O'}{a};
does the trick as does:
print %{'hell' . lc 'O'}->{a};
however, under "use strict", this fails, since %hello isn't declared
with "my".
If I do put a my in front of the %hello declaration, the print
statement gives me nothing.
I have a sinking suspicion that the above code is wrong, dangerous,
and error prone since I'm not even sure why it works.
What is the proper way to do such a thing?
------------------------------
Date: 15 Apr 2008 19:56:53 GMT
From: xhoster@gmail.com
Subject: Re: Accessing a hash whose name is constructed
Message-Id: <20080415155655.919$Oi@newsreader.com>
Gibbering <roblund@gmail.com> wrote:
> I want to access some data from a hash, but want to build that hash's
> name on the fly... here's the code:
Most likely, you want a multi-level hash.
>
> %hello = (a => 'doggy');
> print ${'hell' . lc 'O'}{a};
>
> does the trick as does:
> print %{'hell' . lc 'O'}->{a};
my %hash;
$hash{hello} = {a => 'doggy'};
print $hash{'hell' . lc 'O'}->{a};
> however, under "use strict", this fails, since %hello isn't declared
> with "my".
Yes indeed, that is one the of things that use strict is there for. The
main one, even.
>
> If I do put a my in front of the %hello declaration, the print
> statement gives me nothing.
You are using two different variables. The lexical %hello, and the global
%main::hello. Since lexicals can't be accessed symbolically, your attempt
at symbolic access (in the absence of use strict) resolved to %main::hello.
Xho
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------------------------------
Date: Tue, 15 Apr 2008 20:08:01 GMT
From: Jürgen Exner <jurgenex@hotmail.com>
Subject: Re: Accessing a hash whose name is constructed
Message-Id: <lg2a049e8qipod83trtbau5qgdmjifqaqk@4ax.com>
Gibbering <roblund@gmail.com> wrote:
>I want to access some data from a hash, but want to build that hash's
>name on the fly... here's the code:
>
>%hello = (a => 'doggy');
>print ${'hell' . lc 'O'}{a};
>
>does the trick as does:
>print %{'hell' . lc 'O'}->{a};
>I have a sinking suspicion that the above code is wrong, dangerous,
>and error prone since I'm not even sure why it works.
See gazillions of previous articles about 'symbolic reference'.
Or just perldoc -q variable ' How can I use a variable as a variable
name?'
>What is the proper way to do such a thing?
Use your own hash instead of the system symbol table. In your case
becasue that would become a HoH (hash of [ref to] hash).
jue
------------------------------
Date: Tue, 15 Apr 2008 12:37:25 -0700 (PDT)
From: Mahesh Asolkar <asolkar@gmail.com>
Subject: How to know if data is piped into my script
Message-Id: <ac5acc86-4ea6-4289-85cc-e60692f54eb8@q10g2000prf.googlegroups.com>
I have the following script:
-----
#!/usr/bin/perl
use strict;
use warnings;
my %hist = ();
my @hist;
$hist{(split /\s+/)[3]}++
foreach (`$ENV{'SHELL'} -c history`);
print map {"$hist{$_} : $_\n"}
sort {$hist{$b} <=> $hist{$a}}
keys %hist;
-----
I want to change it such that it uses '`$ENV{'SHELL'} -c history`'
only if nothing is piped into the script. If I call the script like:
% myscript.pl
It should use '`$ENV{'SHELL'} -c history`'. However if it is called
like:
% history | myscript.pl
It should use the piped in data instead.
What would be the best approach?
Thanks,
Mahesh
------------------------------
Date: 15 Apr 2008 19:48:21 GMT
From: xhoster@gmail.com
Subject: Re: How to know if data is piped into my script
Message-Id: <20080415154823.690$qR@newsreader.com>
Mahesh Asolkar <asolkar@gmail.com> wrote:
> I have the following script:
>
> -----
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my %hist = ();
> my @hist;
>
> $hist{(split /\s+/)[3]}++
> foreach (`$ENV{'SHELL'} -c history`);
>
> print map {"$hist{$_} : $_\n"}
> sort {$hist{$b} <=> $hist{$a}}
> keys %hist;
> -----
Assuming it is safe to load all input into memory at once:
my @x=<>;
foreach (@x? @x : `$ENV{'SHELL'} -c history`) {
This will do what <> does, not just pipes. If you want only STDIN, and
only when STDIN is hooked up to a pipe, then maybe:
foreach (-p STDIN ? <STDIN> : `$ENV{'SHELL'} -c history`) {
Xho
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------------------------------
Date: Tue, 15 Apr 2008 21:49:06 +0200
From: Frank Seitz <devnull4711@web.de>
Subject: Re: How to know if data is piped into my script
Message-Id: <66kf62F2kl8ufU7@mid.individual.net>
Mahesh Asolkar wrote:
>
> It should use '`$ENV{'SHELL'} -c history`'. However if it is called
> like:
>
> % history | myscript.pl
>
> It should use the piped in data instead.
unless (-t) {
# STDIN is not opend to a tty but a file or pipe
}
Frank
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------------------------------
Date: 15 Apr 2008 19:40:09 GMT
From: xhoster@gmail.com
Subject: Re: Print a separator between each iteration of a foreach loop
Message-Id: <20080415154011.916$h7@newsreader.com>
Ben Morrow <ben@morrow.me.uk> wrote:
> Quoth xhoster@gmail.com:
> > ShaunJ <sjackman@gmail.com> wrote:
> > > I want to print a separator between each iteration of a foreach loop,
> > > but not after the last element. How do I avoid printing the last
> > > extraneous comma in the following code snippet?
> > >
> > > foreach (@ARGV) {
> > > print $_, ',';
> > > }
> > > print "\n";
> > >
> > > In this simple example join ',' would suffice, but the real body of
> > > the foreach loop is more complicated.
> >
> > Unless it is huge, you could just change the print to be push @results,
> > $_; and then do the join on @results.
>
> print join ',', map {...} @ARGV; is cleaner than pushing onto an
> intermediate array.
Sure, but I thought he was hinting that the contents of the loop were more
complex than shown, and hence would be more complex than comfortable in a
map block. Of course, different people do have different comfort levels
when it comes to cramming complexity into map blocks.
> Or you can set $, and $\ and avoid the join and "\n"
> altogether.
Sure, but then I'd have look up which ones are which (I don't use them
enough to remember $, from $" from $;, and $\ from $/) and then I'd worry
about whether I should change them globally (i.e. will code later on use
them implicitly and get confused, either now or with likely future
evolution of the script) or if I need to localize them and then go look up
the details of localizing punctuation variables. Easier to just use join,
which I don't need to look up. So basically, I don't use them because I
don't use them enough to feel comfortable using them without looking things
up, kind of a self-reinforcing situation.
A Freudian analysis of Perl programming technique.
Xho
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------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
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Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V11 Issue 1451
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