Dynamically capture output of system command in Perl

Question

In my Perl code, I use a system command to run a script. I'm using Gtk2::Perl and Glade to build a UI. I need the output of the command to be captured not just to the console (which Capture::Tiny does), but also to a TextView in my GUI.

system("command");

$stdout = tee{                         #This captures the output to the console
system("command");  
};

$textbuffer->set_text($stdout);       #This does set the TextView with the captured output, but *after* the capture is over.

Any help would be greatly appreciated.

I need the output of system to be captured in the TextView simultaneously with its capture on the console. That's not happening. — Anupama G
– Anupama G, Commented Jun 30, 2015 at 9:11

mpapec · Accepted Answer · 2015-06-30 10:18:55Z

4

If you're trying to 'capture' the output of a system call, then I would suggest the best approach is to use open and open a filehandle to your process:

my $pid = open ( my $process_output, '-|', "command" );

Then you can read $process_output exactly as you would a file handle (bear in mind it'll block if there's no IO pending).

while ( <$process_output> ) { 
   print; 
}

close ( $process_output );

You can 'fake' the behaviour of system via the waitpid system call:

 waitpid ( $pid, 0 );

This will 'block' your main program until the system call has completed.

edited Jun 30, 2015 at 10:18

mpapec

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answered Jun 30, 2015 at 9:34

Sobrique

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3 Comments

Anupama G Over a year ago

Thank you. I suppose the use of open is my best bet. Will do this!

Anupama G Over a year ago

This is very useful but does not really solve my problem, actually - the output is not dynamically updated in the TextView as it is generated. There is a distinct delay, sadly.

Sobrique Over a year ago

Look up autoflush in the IO::handle docs. Open like this is already running in a parallel process.

Community · Accepted Answer · 2017-05-23 12:15:59Z

2

What you want to do is not possible with system(). System() forks a new process and waits for it to terminate. Then your program continues (see manual). You could start a sub-process (executing whatever system() did for you) and read this sub-process' stdout. You could for example get inspired here: redirecting stdin/stdout from exec'ed process to pipe in Perl

edited May 23, 2017 at 12:15

CommunityBot

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answered Jun 30, 2015 at 9:12

Matthias

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1 Comment

Anupama G Over a year ago

Ah, I see. I expected to be able to do something with system(), as this capture is the only thing lacking. Thanks a lot!

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