Question

#!/usr/bin/perl

use strict;
use warnings;

open(my $vmstat, "/usr/bin/vmstat 1 2>&1 |");
open(my $foo, ">", "foo.txt") or die "can't open it for write";

while(<$vmstat>) {
   print "get ouput from vmstat and print it to foo.txt ...\n";
   print $foo $_;
}

when I run the above code, nothing wrong happend.but after I press ctr-c to quit, nothing in the foo.txt. could any of you tells me why does this happen? thanks in advance.

Answer 1

Maybe the output is being buffered and you are not being patient enough. Try this extra line of code:

open(my $foo, ">foo.txt") or die "can't open it for write";
select $foo; $| = 1; select STDOUT;