Perl script to check disk usage

Question

I'm looking for input on the code itself and formatting/style. This script parses the output of df -h on a Linux server and emails the user if the usage percentage is above the threshold (90% in this case).

#!/usr/bin/perl
use warnings;
use strict;
use Mail::Sendmail;
my $svr = `hostname`;
my @output = `df -h`;
my $msg;
my $mailto = '[email protected]';
my $threshold = 90;
sub main
{
 foreach (@output) {
 if (($_ =~ m/(\d+)% (.*)/) && ( 1ドル > $threshold )) {
 chomp($svr); $msg = "$svr: 2ドル volume is 1ドル percent full\n" }
 }
 my %mail = ( To => $mailto,
 From => '[email protected]',
 Subject => "$svr has a full file system",
 Message => $msg
 );
 if ( defined $msg ) {
 sendmail(%mail) or die $Mail::Sendmail::error;
 }
}
main

Answer 1

There is a bug here:

foreach (@output) {
 if (($_ =~ m/(\d+)% (.*)/) && ( 1ドル > $threshold )) {
 chomp($svr); $msg = "$svr: 2ドル volume is 1ドル percent full\n" }
 }

If there are more than one partitions full, $msg will contain only the last one. I think you want to append to $msg instead of overwriting. I suggest to rewrite like this:

chomp(my $svr = `hostname`);
foreach (@output) {
 if (m/(\d+)% (.*)/ && 1ドル > $threshold) {
 $msg .= "$svr: 2ドル volume is 1ドル percent full\n";
 }
}

Explanation of other improvements:

• Removed unnecessary brackets from the if condition
• Simplified $_ =~ m// to just m// which does the same
• Instead of chomp($svr) for each line, do it only once, right after initialization
• Reindented, so it's easier to see the block of code that belongs to the loop

Lastly, you can drop "defined" in if ( defined $msg ) {

• Gregg Leventhal: All excellent improvements, thanks! I will make these changes to the code.