You can't get the status of the command by using backticks; that's not what they're for (they're used if you want to capture the output of the command.) If you want the status, you need to use the 'system' function. Here, I'm going to loop-mount an ISO file on a directory in /tmp, then unmount it - with error checking:

#!/usr/bin/perl -w
use strict;

system "sudo mount $ARGV[0] /tmp/mnt -o loop=/dev/loop0"
    and die "mount: ", $? >> 8, "\n";
print "Mounted successfully.\n";
system "sudo umount /tmp/mnt -l" and die "umount: ", $? >> 8, "\n";
print "Unmounted successfully.\n";
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And here's the output:

ben@Jotunheim:/tmp$ ./mt ubuntu_9_10.iso 
Mounted successfully.
Unmounted successfully.
ben@Jotunheim:/tmp$ ./mt fake_filename
fake_filename: No such file or directory
mount: 32
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The return code from 'mount', 32, is listed in the man page as 'mount failure'.