Hope this snippet would help,

my $g_cmd="ssh Machinename ls <completefilepath>";
`$g_cmd`;
if($?)
{
    print "Error doesnot exist";
}
else
{
    $g_cmd="scp local_file remotehost:targetdirectory/remote_file";
    `$g_cmd`;
}
[download]

if it's a directory you want to test add -d switch to the ls command.