use strict;
use warnings;

use Net::Netrc;
use Net::Rexec qw( rexec );

foreach my $host (qw( host1 host2 host3 )) {
    my $machine;
    unless ($machine = Net::Netrc->lookup ($host)) {
        warn "Machine $host not found in .netrc\n";
        next;
        }
    my ($user, $password) = $machine->lpa;
    my ($rc, @out) = rexec ($host, "df -k", $user, $password);
    foreach my $df_line (@out) {
        # ...
        }
    }