use strict;
use warnings;
use Data::Dumper;

my @config =
  (
   '/home       filer1232:/vol/home1',
   '/mystuff    filer1233:/vol/project',
   '/data       filer1234:/vol/example_data',
   '/software   filer1255:/vol/my_software',
   '/tools      filer1235:/vol/my_tools',
   '/docs       filer146:/vol/my_documents',
  );


my @mounted =
  (
   '/home       filer1232:/vol/home1',
   '/mystuff    filer1233:/vol/project',
   '/data       filer1234:/vol/example_data',
   '/tools      filer1235:/vol/my_tools',
  );

my %diff;
@diff{@config}=();

delete @diff{@mounted};

print Dumper [keys %diff];