open(FH, 'cut -d" " -c6 file|') or die $!;
# or open(FH, "awk '{print \$6}' file|") ...
while(<FH>) {
...
}
close FH or die $!; # Check close on pipe opens

# Also, you might try a regex which
# uses qr and only saves what you want
my $re = qr/(?:\S+\s+){5}(\S+)/;
...
while (<FH>) {
 next unless $_ =~ $re;
 my $field = $1;
...
}