ARDUINO & DD-WRT

Using Arduino Networking, Protocols, and Devices
3

a bit of progress; with this code I am able to read and write from/to my terminal:

arduino code:

int incomingByte = 0;   // for incoming serial data
void setup() {
        Serial.begin(115200);     // opens serial port, sets data rate to 9600 bps
        Serial.write("Hi, I am alive!");
}

void loop() {

        if (Serial.available() > 0) {
                // read the incoming byte:
                incomingByte = Serial.read();

                Serial.print("I received: ");
                Serial.println(incomingByte, DEC);
        }
}

by using these commands on my terminal

to write: echo "Here I am" > /dev/tty.usbserial-A9007VSI 115200
to read: screen  /dev/tty.usbserial-A9007VSI 115200

but when I SSH login to my router the above commands do not work,
when I try this command:

echo "Here I am" > /dev/tty.usbserial-A9007VSI 115200

I get this message:

-sh: can't create /dev/tty.usbserial-A9007VSI: Permission denied

any hint how to write to serial from within my dd-wrt SSH login much appreciated