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I'm still learning some of the basic element of Perl. In the
following segment,

#!/usr/bin/perl -w
use strict;
use OpenGL qw/ :all /;
use Math::Trig;
eval 'use Time::HiRes qw( gettimeofday )';
my $hasHires = !$@;
$|++;

The last two lines above, what is occurring? I don't understand the
purpose of "!$@", is it related to error handling of the previous eval
command? What's "$|++;" doing? I understand that $| is something
related to flushing piped output.

Later on in the script:
my $now = $hasHires ? gettimeofday() : time();

What's the function of "?" in this context?

Thanks,

-Ben

Ben wrote:
> I'm still learning some of the basic element of Perl. In the
> following segment,
>
> #!/usr/bin/perl -w
> use strict;
> use OpenGL qw/ :all /;
> use Math::Trig;
> eval 'use Time::HiRes qw( gettimeofday )';

Loads the Time::HiRes module at run time; eval() prevents that the
program dies for the case Perl fails to find Time::HiRes.

> my $hasHires = !$@;

If Time::HiRes was found, the $@ variable contains a null string, i.e. a
false value. !$@ means that a true value is assigned to $hasHires.

perldoc -f eval

> $|++;

Sets $| to a true value (adds 1). See "perldoc perlvar" about the
meaning of $|.

> Later on in the script:
> my $now = $hasHires ? gettimeofday() : time();
>
> What's the function of "?" in this context?

See "perldoc perlop", the "Conditional Operator" section.

Personally I find the coding style somewhat obfuscated. I would probably
have said something like:

my $noHires = $@;

and later:

my $now = $noHires ? time() : gettimeofday();

But that's probably just a matter of taste.

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Thank you Gunnar for a friendly and helpful response!

Perldoc is my new friend.

-Ben

On Apr 12, 6:02*pm, Gunnar Hjalmarsson <nore...@gunnar.cc> wrote:
> Ben wrote:
> > I'm *still learning some of the basic element of Perl. *In the
> > following segment,
>
> > * #!/usr/bin/perl -w
> > * use strict;
> > * use OpenGL qw/ :all /;
> > * use Math::Trig;
> > * eval 'use Time::HiRes qw( gettimeofday )';
>
> Loads the Time::HiRes module at run time; eval() prevents that the
> program dies for the case Perl fails to find Time::HiRes.
>
> > * my $hasHires = !$@;
>
> If Time::HiRes was found, the $@ variable contains a null string, i.e. a
> false value. !$@ means that a true value is assigned to $hasHires.
>
> * * *perldoc -f eval
>
> > * $|++;
>
> Sets $| to a true value (adds 1). See "perldoc perlvar" about the
> meaning of $|.
>
> > Later on in the script:
> > * *my $now = $hasHires ? gettimeofday() : time();
>
> > What's the function of *"?" in this context?
>
> See "perldoc perlop", the "Conditional Operator" section.
>
> Personally I find the coding style somewhat obfuscated. I would probably
> have said something like:
>
> * * *my $noHires = $@;
>
> and later:
>
> * * *my $now = $noHires ? time() : gettimeofday();
>
> But that's probably just a matter of taste.
>
> --
> Gunnar Hjalmarsson
> Email:http://www.gunnar.cc/cgi-bin/contact.pl

jbenjam <> wrote:


> Perldoc is my new friend.


Since you did not put the subject of your article in the Subject of
your article, included "newbie" in your Subject, top-posted,
quoted a .sig and did not know about perldoc, I assume that you have
not yet seen the Posting Guidelines that are posted here frequently.

It contains many pointers that will help you get solutions to
Perl programming problems.


http://www.rehabitation.com/clpmisc.shtml


--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"

Tad J McClellan wrote:
> jbenjam <> wrote:
>>
>> Perldoc is my new friend.
>
> Since you did not put the subject of your article in the Subject of
> your article,

Your criticizing of the subject is somewhat misplaced this time IMO.

> http://www.rehabitation.com/clpmisc.shtml

But the posting guidelines are always a good idea to study.

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

In article <>,
Gunnar Hjalmarsson <> wrote:
>Ben wrote:
>> [stuff]
>Personally I find the coding style somewhat obfuscated. I would
>probably have said something like:
>
> my $noHires = $@;

I now know the rules on what's considered "true", but personally, if I
use a variable in a boolean context, I prefer it to be a clear
boolean, such as the result of a boolean operator, if for no other
reason than documentation. So I'd do
my $hasHires = ($@ eq '');

>> $|++;
>
>Sets $| to a true value (adds 1). See "perldoc perlvar" about the
>meaning of $|.

Turning on autoflush with an increment is ridiculous, when they could
just as easily do
$| = 1;
and have it actually work in all cases (assuming autoflush is
implemented at all). It makes me want to start the program with
$| = -1; # sets $| to a true value, so it should autoflush
just to show how bad an increment is.

--
Tim McDaniel,

In article <qn0ib6->,
Ben Morrow <> wrote:
>
>Quoth :
>> Turning on autoflush with an increment is ridiculous, when they
>> could just as easily do
>> $| = 1;
>> and have it actually work in all cases (assuming autoflush is
>> implemented at all). It makes me want to start the program with
>> $| = -1; # sets $| to a true value, so it should autoflush
>> just to show how bad an increment is.
>
>Oh, but it *does* work in all cases. $| is magical, remember.
>
> ~% perl -le'$| = -1; print $|'
> 1
> ~% perl -le'$| = 1; $|++; print $|'
> 1
> ~% perl -le'$| = -1; $|++; print $|'
> 1

You. MUST. Be. Shitting. Me.

[checking]
It does just that under Perl 5.00502 and 5.010000. Gahhh ...

>Whether your find this amusing or obscene probably depends on your
>sense of humour

Obscene, highly counter-intuitive, and undocumented:

$| If set to nonzero, forces a flush right away and after every
write or print on the currently selected output channel.
Default is 0 (regardless of whether the channel is really
buffered by the system or not; $| tells you only whether you've
asked Perl explicitly to flush after each write). ...

>(I don't understand what you mean by 'assuming autoflush is implemented
>at all'. AFAIK autoflush is always implemented...)

Weasel-wording: I was afraid that, if I left it out, someone would
mock my ignorance of the fact that the port to Irish Business Machines
System/42 did nothing with $|.

--
Tim McDaniel,