command output

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Hi,

i am running system command using following line in perl script

($stdout,$stderr) = capture_exec("$workspace\\Dev_Tools\\Nant\\bin\\nant -buildfile:abc.build $target");
print "$stdout\n";
print "$stderr\n";


now the issue is , the contents of these variable gets printed on console after this command gets executed
i need to print the output of this command as it is executed
what does it mean that, whenever there is a new entry in these variable, it should print that immediately on console

please suggest

regards
irfan

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Re: command output

On 11/05/2011 13:12, Irfan Sayed wrote:
>
> i am running system command using following line in perl script
>
> ($stdout,$stderr) = capture_exec("$workspace\\Dev_Tools\\Nant\\bin\\nant -buildfile:abc.build $target");
> print "$stdout\n";
> print "$stderr\n";
>
>
> now the issue is , the contents of these variable gets printed on console after this command gets executed
> i need to print the output of this command as it is executed
> what does it mean that, whenever there is a new entry in these variable, it should print that immediately on console

Hi Irfan

You don't show the code for capture_exec, but your purpose is probably
best served by a pipe open on the command's output. To see the output in
real time you would also need to enable autoflush by setting the system
variable $| to true. Something like this:


use strict;
use warnings;

my $cmd = "$workspace\\Dev_Tools\\Nant\\bin\\nant -buildfile:abc.build
$target";
open my $ch, "$cmd |" or die $!;

local $| = 1;

while (my $line = <$ch>) {
print $line;
}


If you want the output to stderr to be merged with the standard output,
then you could change the open statement to look like this:


open my $ch, "$cmd 2>&1 |" or die $!;


HTH,

Rob

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Re: command output

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thanks rob.
is there any another shorter way??
capture_exec is just external perl module from cpan. i am just using it as it is


regards,
irfan



________________________________
From: Rob Dixon
To: Perl Beginners
Cc: Irfan Sayed
Sent: Wednesday, May 11, 2011 6:37 PM
Subject: Re: command output




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Re: command output

On 11/05/2011 14:14, Irfan Sayed wrote:
> On 11/05/2011 14:06, Rob Dixon wrote:
>> On 11/05/2011 13:12, Irfan Sayed wrote:
>>>
>>> i am running system command using following line in perl script
>>>
>>> ($stdout,$stderr) =
>>> capture_exec("$workspace\\Dev_Tools\\Nant\\bin\\nant
>>> -buildfile:abc.build $target");
>>> print "$stdout\n";
>>> print "$stderr\n";
>>>
>>>
>>> now the issue is , the contents of these variable gets printed on
>>> console after this command gets executed
>>> i need to print the output of this command as it is executed
>>> what does it mean that, whenever there is a new entry in these
>>> variable, it should print that immediately on console
>>
>> You don't show the code for capture_exec, but your purpose is probably
>> best served by a pipe open on the command's output. To see the output in
>> real time you would also need to enable autoflush by setting the system
>> variable $| to true. Something like this:
>>
>>
>> use strict;
>> use warnings;
>>
>> my $cmd = "$workspace\\Dev_Tools\\Nant\\bin\\nant -buildfile:abc.build $target";
>> open my $ch, "$cmd |" or die $!;
>>
>> local $| = 1;
>>
>> while (my $line = <$ch>) {
>> print $line;
>> }
>>
>>
>> If you want the output to stderr to be merged with the standard output,
>> then you could change the open statement to look like this:
>>
>>
>> open my $ch, "$cmd 2>&1 |" or die $!;
>
> thanks rob.
> is there any another shorter way??
> capture_exec is just external perl module from cpan. i am just using it as it is

Ah, then I assume you are using IO::CaptureOutput? We cannot know the
functionality of all the CPAN modules, so please say if you are using a
module. Better still, post the entirety of your code.

I am surprised you think this solution is too long for you. A large
proportion of it is the command line that you posted, followed by an
open, enabling flushing, and a loop that must exist for any solution.
Maybe it would help if I rewrote it as a subroutine?


use strict;
use warnings;

display_exec("$workspace\\Dev_Tools\\Nant\\bin\\nant -buildfile:abc.build $target");

sub display_exec {
my $cmd = shift;
open my $ch, "$cmd |" or die $!;
local $| = 1;
print while <$ch>;
}


Please can you explain more about your problem, and what you want to do
with the output from the shell command?

Rob

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Re: command output

On 11/05/2011 14:14, Irfan Sayed wrote:
> thanks rob.
> is there any another shorter way??
> capture_exec is just external perl module from cpan. i am just using it as it is

If all you want is to be able to see the output from the command, have
you considered

system("$workspace\\Dev_Tools\\Nant\\bin\\nant -buildfile:abc.build $target");

which forks a process with the same stdout and stderr? Or even

exec("$workspace\\Dev_Tools\\Nant\\bin\\nant -buildfile:abc.build $target");

if the command is the last thing for the Perl script to do?

Rob

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