sub has_mounted_home {
    my $uid = shift || die 'Wrong Parameters!\n';

    my @userinfo = getpwnam("$uid");
    # $uid not found:
    return if @userinfo == 0;

    my $local_homedir = $userinfo[7];

    # perhaps use Linux::Mounts instead of:
    my $mount_result  = `/bin/mount | /bin/grep $local_homedir`;

    # needs improvement because /homes/user1 will match e.g. /homes/user12 ...
    return $mount_result ne ""; 
}

foreach my $uid ('uid1', 'uid2', 'uid3') {
    print "$uid has a mounted home\n" if has_mounted_home($uid);
}