Alien has asked for the wisdom of the Perl Monks concerning the following question:

Hi !

How could the output of the top program ( and programs similar to it ) could be captured in a script ?

I tried using $var=`top` , and even opened it with a pipe , it can read the first screen but no more than that.

Thanks!

Replies are listed 'Best First'.
Re: Capturing top-like program output
by Util (Priest) on Jan 06, 2007 at 18:44 UTC 
    while (1) {
    my $top_output = `top -l 1`;
    do_something_with( $top_output );
    sleep 5;
}

    [download]
    From `man top`:
    -l <samples>
    Use logging mode and display <samples> samples, even if standard output is a terminal. 0 is treated as infinity. Rather than redisplaying, output is periodically printed in raw form.
[reply]
[d/l]
Re: Capturing top-like program output
by dorko (Prior) on Jan 06, 2007 at 18:51 UTC
    Try taking a look at the man pages for top. If you open it in batch mode (-b) with a single iteration (-n 1), I'm guessing you could capture the output of a single update from top. Process that output, save it, display it or whatever you wanted to do with it, then fetch another screen of output.

    Completely untested: 

    my $n = 1;
while( $n < 5 ) {
    # capture a single screen's worth of output...
    my $temp = `top -b -n 1`;

    # process $temp here...

    # play nice
    sleep 15;

    $n = $n + 1;
    }

    [download]

    Cheers,

    Brent

    -- Yeah, I'm a Delt.
[reply]
[d/l]
[select]

      I realize that that -b switch is the simplest answer to Alien's question, but personally, I still wonder how you would capture raw console writes from perl.

      -Paul

[reply]
        Me too :)
[reply]
Re: Capturing top-like program output
by zentara (Cardinal) on Jan 06, 2007 at 20:35 UTC
    There are a few ways of dealing with top, this one works pretty well. 
    #!/usr/bin/perl
use warnings;
use strict;
use IPC::Open3;
use IO::Select;

my $pid = $$;

my $pid1 = open3(0, \*READ,\*ERROR,"top -d 1 -b -p $pid ");
#if \*ERROR is false, STDERR is sent to STDOUT

my $sel = new IO::Select();

$sel->add(\*READ);
$sel->add(\*ERROR);

my($error,$answer)=('','');

while(1){

foreach my $h ($sel->can_read){
    my $buf = '';
        if ($h eq \*ERROR){
              sysread(ERROR,$buf,4096);
              if($buf){print "ERROR-> $buf\n"}
}else{

 sysread(READ,$buf,4096);
    if($buf){print "$buf\n"}
   }
  }
}

    [download]
    I'm not really a human, but I play one on earth. Cogito ergo sum a bum
[reply]
[d/l]

Back to Seekers of Perl Wisdom