can't write to file using print

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

There are a couple of issues with this line:

opne(my $foo, ">" "foo.txt") or die "can't open it for write";

First of all, open is misspelled. Also, you have two strings next to each other, with nothing separating them. Try this:

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

Also, if that doesn't fix your problem, double check that you (or the user this runs as) has write access to the file foo.txt.

Answer 2

You have a typo: "opne" instead of "open".

Also, to read from processes, you must put a pipe at the end:

#!/usr/bin/perl

use strict;
use warnings;

open(my $vmstat, "/usr/bin/vmstat 1 5 2>&1 |") or die "error";
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 $_;
}

Answer 3

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;