use strict;
use warnings;

my @array1 = split /\n/, <<END1;
/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
END1

my @array2 = split /\n/, <<END2;
/home       filer1232:/vol/home1
/mystuff    filer1233:/vol/project
/data       filer1234:/vol/example_data
/tools      filer1235:/vol/my_tools
END2

my %currMounted = map { $_ => 1 } @array2;

print "$_\n" for grep !$currMounted{$_}, @array1;