The following is the latest incarnation of something I wrote a few years back, and have refined as I have learned new tricks. The output of the df -k command is filtered for a list of directories. If the free space has changed since I last ran the command, it is stored. I also store a timestamp along with it, in case I want to look at historical trends. Right now, it keeps only the latest 8 reports.

#!/usr/bin/perl
# List free space left
use strict;
use warnings;
use Storable;

my $storable_file = '/home/edi/howard/dfk.storable';
my (@reports);
@reports = @{retrieve($storable_file)} if ( -e $storable_file);

my %new = map {(split /\s+/,$_)[6,3]} grep {/home|archive|edi_store/} 
+`df -k`;
$new{'timestamp'} = time;

unshift @reports, \%new;
if (print_report(@reports[0,1])) {
  pop @reports if (scalar @reports > 7);
  store(\@reports,$storable_file);
}

sub print_report {
  my ($nhr,$ohr) = @_;
  my $change_flag = defined $ohr ? 0 : 1;
  foreach my $key ( keys %{$nhr}) {
    next if $key eq 'timestamp';
    if (defined $ohr->{$key} && $ohr->{$key} ne $nhr->{$key}) {
      printf "%-17s was: %3s now: %3s\n", $key, $ohr->{$key}, $nhr->{$
+key};
      $change_flag = 1;
    } else {
      printf "%-17s: %3s\n",$key,$nhr->{$key}
    }
  }
  return $change_flag;
}
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