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hi

I am trying to store the return value of system command after execution in a forking server.

The command executes successfully but returns "-1". In case of failure, it returns the same value
"-1", like when i am replacing "date" with "data" in system command. From my understanding, it
should return -1 only in case of failure. How do go about distinguishing between a success and
failure call while using the system commnad?

Code:-
-----------------------------------------------------------------------------------
#!/usr/bin/perl -w
use strict;
use IO::Socket;
use IO::Select;

$SIG{CHLD} = 'IGNORE';

my $sock = new IO::Socket::INET(
LocalHost => '10.0.0.23',
LocalPort => '36545',
Proto => 'tcp',
Listen => SOMAXCONN,
Reuse => 1);
$sock or die "no socket :$!";

REQUEST:
while (my $sNew_Socket = $sock->accept())
{
my $kid=fork();
if ($kid)
{
close $sNew_Socket;
next REQUEST;
}

close $sock;
my $obSelected_Socket = IO::Select->new($sNew_Socket);
my $sData_Recevied;
while( $obSelected_Socket->can_read(20))
{
my $sBuffer;
sysread($sNew_Socket,$sBuffer,1<<10);
$sData_Recevied.=$sBuffer;
if($sBuffer =~/\/END>/)
{
last;
}
}
my $sDatecmd=system("date");
$sNew_Socket->send($sDatecmd);
exit;
}

-----------------------------------------------------------------------------------------------------


Thanks

Vikrant

vikrant <> wrote in comp.lang.perl.misc:
> hi
>
> I am trying to store the return value of system command after execution
> in a forking server.
>
> The command executes successfully

How do you know that?

> but returns "-1". In case of failure,
> it returns the same value
> "-1", like when i am replacing "date" with "data" in system command.

Is "date" on the search path of the process that's trying to execute
it?

> From my understanding, it
> should return -1 only in case of failure. How do go about distinguishing
> between a success and
> failure call while using the system commnad?

See perldoc -f system. Note the third paragraph beginning with "The
return value is..."

Anno
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On Thu, 22 Sep 2005 11:38:23 +0530, vikrant said:
> I am trying to store the return value of system command after execution in a forking server.
>
> The command executes successfully but returns "-1". In case of failure, it returns the same value
> "-1", like when i am replacing "date" with "data" in system command. From my understanding, it
> should return -1 only in case of failure. How do go about distinguishing between a success and
> failure call while using the system commnad?

Well, do you know what it returns on success?

perl -e 'printf "[%d]\n", system "date"'

> ...
> my $sDatecmd=system("date");
> $sNew_Socket->send($sDatecmd);

How about:

$sNew_Socket->send($sDatecmd? "Failed" : "Succeded");

Though perhaps you actually wanted the *output* of the date
command? See perldoc -q "output of a command".

You might also care to try the builtins instead:

perl -le 'print scalar localtime'

So the above would be

my $date = scalar localtime;
$sNew_Socket->send($date);

--Damian

vikrant <> wrote:
> hi
>
> I am trying to store the return value of system command after execution
> in a forking server.
>
> The command executes successfully but returns "-1".

How do you know?

> In case of failure,
> it returns the same value "-1", like when i am replacing "date" with
> "data" in system command. From my understanding, it should return -1 only
> in case of failure. How do go about distinguishing between a success and
> failure call while using the system commnad?

Maybe, if Perl is telling you that it fails, you should ask Perl why it
fails.


>
> Code:-
> -------------------------------------------------------------------------
> ---------- #!/usr/bin/perl -w
> use strict;
> use IO::Socket;
> use IO::Select;
>
> $SIG{CHLD} = 'IGNORE';

After asking Perl why it fails, I've decided this is your problem.

....
> my $sDatecmd=system("date");
> $sNew_Socket->send($sDatecmd);

$sNew_Socket->send("$sDatecmd $!");

> exit;
> }
>
> -------------------------------------------------------------------------
> ----------------------------
>
> Thanks
>
> Vikrant

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Anno Siegel wrote:
> vikrant <> wrote in comp.lang.perl.misc:
> > hi
> >
> > I am trying to store the return value of system command after execution
> > in a forking server.
> >
> > The command executes successfully
>
> How do you know that?
>
> > but returns "-1". In case of failure,
> > it returns the same value
> > "-1", like when i am replacing "date" with "data" in system command.
>
> Is "date" on the search path of the process that's trying to execute
> it?
>
> > From my understanding, it
> > should return -1 only in case of failure. How do go about distinguishing
> > between a success and
> > failure call while using the system commnad?
>
> See perldoc -f system. Note the third paragraph beginning with "The
> return value is..."
>

I suspect the most likely scenario is that "date" succeeded but
that wait returned -1 because of the auto-reaping of "IGNORE".

>From perlipc:
...
Setting "$SIG{CHLD}" to "'IGNORE'" on such a platform has
the effect of not creating zombie processes when the parent
process fails to "wait()" on its child processes (i.e. child
processes are automatically reaped). Calling "wait()" with
"$SIG{CHLD}" set to "'IGNORE'" usually returns "-1" ...

perl -le '$SIG{CHLD}="IGNORE";print system "date"'
Thu Sep 22 20:06:29 PDT 2005
-1

--
Charles DeRykus

hi

Due to some problem i could not connect to news group thats why i am
replying using google news group.

wrote:

> > How do you know that?

when i am running my script on terminal
perl server.pl
It shows the following output on the terminal after accepting the
client request.
Mon Sep 26 11:49:16 IST 2005

> > See perldoc -f system. Note the third paragraph beginning with "The
> > return value is..."
as u told i go through it and able to understand what exactly
happened,same as Charles DeRykus said to me .
Calling "wait()" with "$SIG{CHLD}" set to "'IGNORE'" usually returns
"-1" that's what i got through send function
$sNew_Socket->send($sDatecmd);
but if i comment out the $SIG{CHLD}='IGNORE' then zombies are created.
Also, date is not just i what to run . i am using it here just to test
the system command output in forking server.

>
> I suspect the most likely scenario is that "date" succeeded but
> that wait returned -1 because of the auto-reaping of "IGNORE".

> >From perlipc:
> ...
> Setting "$SIG{CHLD}" to "'IGNORE'" on such a platform has
> the effect of not creating zombie processes when the parent
> process fails to "wait()" on its child processes (i.e. child
> processes are automaticaly reaped).
>
> perl -le '$SIG{CHLD}="IGNORE";print system "date"'
> Thu Sep 22 20:06:29 PDT 2005
> -1
so,please suggest me how do i get the system command output in forking
server.

Thanks
vikrant