From perldoc -f system:

The return value is the exit status of the program as
returned by the "wait" call.  To get the actual exit
value shift right by eight (see below).  See also "exec".

[snip]

You can check all the failure possibilities by inspecting $?
like this:

   $exit_value  = $? >> 8;
   $signal_num  = $? & 127;
   $dumped_core = $? & 128;

or more portably by using the W*() calls of the POSIX exten-
sion; see perlport for more information.
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This isn't intended as an insult or anything, I just want you to get the best help in the most efficient way:

This question is quite thoroughly answered in the documentation shipped with perl. I suggest you take a look at perldoc -f system (try man perlfunc on a Debian system without perldoc) for starters. This documentation is also available online at system.

Usually, the first place to look for info is perltoc which is a huge table of contents for things in the perl documentation. This has links to the perl FAQs, which are a fairly helpful resource as well.

my $result=`sudo /bin/mount /dev/fd0 /mnt/floppy`;
if ($?) {  # there was an non zero return code
    print "There was an error: $?\n";
    print $result
} else {
    # looks like it worked
}
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With system you get the exit code of the forked child returned, perldoc suggests the following to handle errors.

if ($? == -1) {
    print "failed to execute: $!\n";
    }
    elsif ($? & 127) {
    printf "child died with signal %d, %s coredump\n",
        ($? & 127),  ($? & 128) ? 'with' : 'without';
    }
    else {
    printf "child exited with value %d\n", $? >> 8;
    }
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