If you don't want to use perl modules you probably need to script SCP(1). Here is an edited bit of code from a backup script that should get you started

my $SCP         = '/usr/bin/scp';
my $KEYFILE     = '/root/.ssh/id_rsa';
my $CVS         = "$BACKUP/CVS-$REMOTE_HOST";
my $REMOTE_PATH = "$REMOTE_USER\@$REMOTE_HOST:$REMOTE_PATH";
my $res = `$SCP -o Protocol=2 -i $KEYFILE -c blowfish -B -p $REMOTE_PA
+TH $CVS 2>&1`;
$res =~ s/[^\n\040-\177]//g;
warn $res ? "scp failed and returned:\n$res\n\n" : "scp succeeded!\n\n
+";
[download]