At 01:17 PM 7/3/02 -0700, drieux wrote:
>volks,
>
>I am trying to help with understanding
>'what is basic/beginner' level - so I
>have tried to put together a step by step
>walk through from the simple concept to
>the code in execution - close to what would
>solve the Problem Description.
>
>So for those of you with 'editorial skills'
>and the time, please review and kvetch with
>me about
>
> http://www.wetware.com/drieux/pbl/perlTrick/CBO/PingIt/
>
>as a way to look at evolving code upward from the
>simple idea....
There's a portability problem with calling `ping $host`. On some
platforms this will result in an indefinite ping. Others do not say
"is alive" but instead give statistics. This is why Net::Ping was
invented, but the problem it has is that it cannot send ICMP pings,
only TCP pings, since you need to be root to ICMP ping and the ping
program is setuid for this purpose. But generally TCP ping is good enough.
You say in #2
# now we could solve our problem with stderr
# the simple way with say
# my $answer=`ping $host 2>&1`;
#
# but let's go for the bigger picture -
and then use a piped open from which you read just the first line, then
close the pipe; but that could result in a SIGPIPE. I do not see the
'bigger picture' you speak of; seems better to me to say
(`ping $host 2>&1`)[0]
to get the first line. And if you're going to encapsulate this in a
subroutine, that subroutine ought to hide the ping output format and
just return true/false, or something in between instead of making the
caller check for the string 'is alive' or whatever their ping is going to say.
In #3 you check for possibilities like the host not existing; IMHO this
is better done before and independently of ping, with something like
if (gethostbyname($host)...)
Incidentally, many people object to the StudlyCaps form of naming,
certainly for subroutines and variable names. They seem not to mind
them in module names.
In #4 you say
# What about a little polymorphism to allow some level of recursion.
#
sub PingHost [...]
I don't get it. I see neither polymorphism nor recursion in that subroutine.
I don't think I could call this ready for Prime Time. It's at variance
with the kind of 'best practices' code examples I'm used to seeing in
the better CPAN modules and the better books. I'd suggest perusing
Lincoln Stein's "Network Programming with Perl" for a bit and see
whether or not you come to the same conclusion.
--
Peter Scott
Pacific Systems Design Technologies
http://www.perldebugged.com/
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