Re: [Nolug] Perl Question

Compare to:

print "this is will not print" if 0;
print "this is will print" unless 0;

When you say a "do-while" loop, you imply that the condition is evaluated
after the loop is run, like Katrina said.
When you say a "while" loop, you mean the condition is evaluated, then the
loop is run.

Perl lets you place conditionals after statements because Larry Wall thinks
it reads more easily. The while construct after a statement is a 'while'
loop, not 'do-while' loop. It is evaluated, and then the loop is run
possibly run followed by another evaluated, etc.

Its just syntactic sugar.

On 6/1/07, John Souvestre <johns@sstar.com> wrote:
>
> Hello Friedrich.
>
>
>
> I think that they question is would happens in:
>
>
>
> print "will I print once or forever" while (1);
>
> It seems to print forever, thus an implied "do" at the beginning of the
> line. ???
>
>
>
> Thanks,
>
> John
>
> John Souvestre - Southern Star - (504) 888-3348 - www.sstar.com
> ------------------------------
>
> *From:* owner-nolug@redfishnetworks.com [mailto:
> owner-nolug@redfishnetworks.com] *On Behalf Of *Friedrich Gurtler
> *Sent:* Friday, June 01, 2007 10:17 AM
> *To:* nolug@nolug.org
> *Subject:* Re: [Nolug] Perl Question
>
>
>
> It cant.
>
> do {
> print "Do while runs code once even though condition is false. This
> will print once";
> } while (0);
>
> while(0)
> {
> print "While loops do not, this wont print";
> }
>
> print "while at the end of statement is a while, not a do-while loop"
> while (0);
>
> On 6/1/07, *John Souvestre* < johns@sstar.com> wrote:
>
> Hi Katrina.I
>
> I understand what you are saying. I was just unaware that the "do while"
> loop
> could be written without actually having a "do". :)
>
> John
>
> John Souvestre - Southern Star - (504) 888-3348 - www.sstar.com
>
> -----Original Message-----
> From: owner-nolug@redfishnetworks.com [mailto:
> owner-nolug@redfishnetworks.com]
> On Behalf Of Katrina Niolet
> Sent: Friday, June 01, 2007 9:00 AM
> To: nolug@nolug.org
> Subject: Re: [Nolug] Perl Question
>
> the difference between:
>
> do {
> code
> } while (condition);
>
> and
>
> while(condition) {
> code
> }
>
> is that in the first it will always happen at least once because the
> condition
> is post-tested; in the second its pre-tested, so if the condition is false
> the block will never execute.
>
> Le Friday 01 June 2007 08:48:39 Friedrich Gurtler, vous avez écrit:
> > Its not skipping the 'do' in the 'do while' loop, its just a 'while'
> loop,
> > ala C, C++, Java, C# etc.
> >
> > If you wanted to perl-ify it (for no reason), you could do something
> like
> >
> > $filename .= rand(10) while ((-f "$filename.tmp") || (-f
> "$filename.sub"));
> >
> > Supposedly thats easier to read, but I don't really get it. Hope this
> > helps.
> >
> > -- Fritz
> >
> > On 6/1/07, John Souvestre <johns@sstar.com> wrote:
> > > Hi Ray.
> > >
> > > Thanks! I did some reading and did find the -f function. But I
> didn't
> > > see
> > > anything about skipping the "do" in the "do while" loop. Can that be
> > > done with
> > > other constructs, too?
> > >
> > > Thanks,
> > >
> > > John
> > >
> > > John Souvestre - Southern Star - (504) 888-3348 - www.sstar.com
> > >
> > > -----Original Message-----
> > > From: owner-nolug@redfishnetworks.com [mailto:
> > > owner-nolug@redfishnetworks.com]
> > > On Behalf Of -ray
> > > Sent: Friday, June 01, 2007 12:12 AM
> > > To: nolug@nolug.org
> > > Subject: Re: [Nolug] Perl Question
> > >
> > >
> > > Yep, that's what it's doing. -f is a function that returns true if
> the
> > > file exists (see man perlfunc). It's just a "do while" loop, that
> keeps
> > > appending a random digit to the filename until you get a filename
> that's
> > > not in use.
> > >
> > > while ((-f "$filename.tmp") || (-f "$filename.sub")) {
> > > $filename .= rand(10);
> > > }
> > >
> > > ray
> > >
> > > On Thu, 31 May 2007, John Souvestre wrote:
> > > > Hi.
> > > >
> > > > I'm trying to figure out a Perl script. One line in it has me
> baffled.
> > > >
> > > > I believe it is intended to extend a filename till it is
> unique. But I
> > >
> > > don't
> > >
> > > > quite grasp the syntax.
> > > >
> > > > $filename .= rand(10) while (-f "$filename.tmp") || (-f
> > >
> > > "$filename.sub");
> > >
> > > > Is this a shorthand way of writing a "do while" loop?
> > > >
> > > > And what does the "-f" do?
> > > >
> > > > Thanks!
> > > >
> > > > John
> > > >
> > > > John Souvestre - Southern Star - (504) 888-3348 - www.sstar.com
> > > >
> > > >
> > > > ___________________
> > > > Nolug mailing list
> > > > nolug@nolug.org
> > >
> > > --
> > > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> > > Ray DeJean http://www.r-a-y.org
> > > Systems Engineer Southeastern Louisiana University
> > > IBM Certified Specialist AIX Administration, AIX Support
> > > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> > >
> > > ___________________
> > > Nolug mailing list
> > > nolug@nolug.org
> > >
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>
>
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Received on 06/01/07