communicating with arduino over serial via terminal I'm attempting to write data over a serial line to the arduino, however I don't want to use the arduino IDE but rather use the command line. 

In order to do this I have the following commands: 

$stty -F /dev/ttyACM0 cs8 9600 ignbrk -brkint -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts
$echo s123 &gt; /dev/ttyACM0


The code on the receiving end checks whatever or not the input is s123 and if it is starts blinking. I have tested this using the arduino IDE and it worked, however this did not work.

The sketch looks like this:

    void loop(){
     if(Serial.available()==4){
       byte b1,b2,b3,b4; 
      b1=Serial.read();
      b2=Serial.read();
      b3=Serial.read();
      b4=Serial.read();     
        if(b1=='s'){
               digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)
               delay(1000);               // wait for a second
               digitalWrite(13, LOW);    // turn the LED off by making the voltage LOW
               delay(1000);               // wait for a second
               digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)
               Serial.println("the cow has landed");
          }
     }


    void setup(){ //////////////SETUP////////////////////////
        Serial.begin(9600);
    }


the output of 

stty -F /dev/ttyACM0 -a


was :

speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = &lt;undef&gt;; eol2 = &lt;undef&gt;; swtch = &lt;undef&gt;; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = ^V; flush = ^O; min = 0; time = 0;
-parenb -parodd cs8 -hupcl -cstopb cread clocal -crtscts
ignbrk -brkint -ignpar -parmrk inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany -imaxbel -iutf8
-opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
-isig -icanon -iexten -echo -echoe -echok -echonl noflsh -xcase -tostop -echoprt -echoctl -echoke


Thank you
This was fixed this morning after a reboot and upgrade command, still don't know which one of these fixed it but it seems to work now.

Ah figured it out we were using the 0 and 1 rx gates to communicate over serial rather then usb and as the used power supply turned out to be only 5V rather then 9-12V it didn't quite work as intended.