my $line = <$INPUT_FH>;
$line = <$INPUT_FH>;
while ($line = <$INPUT_FH>) {
    # process file
}

##</code><code>##

while (my $line = <$INPUT_FH>) {
    # Ignore all lines not beginning with a number
    next unless $line =~ /^\s*\d/;

    # process file
}

##</code><code>##

while (my $line = <$INPUT_FH>) {
    # Ignore the header lines
    next if $line =~ /^(procs|\s*r\s+b\s+swpd)/;

    # process file
}