Here's how I'd do it:

my $mountpath = '/mnt/floppy';
my $device = '/dev/fd0';

my $status = system("mount", $device, $mountpath);
die "Mount failure for $device and $mountpath" unless ($status == 0);
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You might want to put your full path to mount in a variable too. I use the list format system call because it doesn't invoke the shell to parse the arguments. That's a little more secure.