# Loop through serial ports
**URL:** https://discourse.processing.org/t/loop-through-serial-ports/28442
**Category:** Electronics (Arduino, etc.)
**Created:** [March 11, 2021, 4:32pm UTC](https://discourse.processing.org/t/loop-through-serial-ports/28442 "2021-03-11T16:32:45Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Konstanitn](https://discourse.processing.org/u/Konstanitn)
#### Post date: [March 11, 2021, 4:32pm UTC](https://discourse.processing.org/t/loop-through-serial-ports/28442/1 "2021-03-11T16:32:45Z")
Loop through serial ports
Hello,
I am trying to make a while loop for searching of the right serial port. I get the `“RuntimeException: Error opening serial port COM4: Port busy”` error probably because the port connection is still open. For my understanding there should be a command like “close.myPort”.
```auto
while (firstContact == false){
for (int i = 0; i <= Serial.list().length-1; ++i)
{
myPort = new Serial(this, Serial.list()[i], 9600);
val = myPort.readStringUntil('\n');
val = trim(val);
if (val != null)
{
if (val.equals("K"))
{
firstContact = true;
portNumber=i;
myPort.write("O");
println("contact");
}
else {println("no contact");}
}
}
}
```
Sorry if the solution is too simple but I could not google the answer.
---
### Author:  [@micuat](https://discourse.processing.org/u/micuat)
#### Post date: [March 11, 2021, 7:13pm UTC](https://discourse.processing.org/t/loop-through-serial-ports/28442/2 "2021-03-11T19:13:44Z")
I think you cannot simply “close” the port because other applications can be using it. Perhaps you can wrap inside the for loop with try/catch not to abort the program
[https://processing.org/reference/catch.html](https://processing.org/reference/catch.html)
---
### Author:  [@Konstanitn](https://discourse.processing.org/u/Konstanitn)
#### Post date: [March 11, 2021, 11:04pm UTC](https://discourse.processing.org/t/loop-through-serial-ports/28442/3 "2021-03-11T23:04:39Z")
To clarify, the for loop (first run) works in the example above. The error occurs when it get called second time, because it can’t do `myPort = new Serial(this, Serial.list()[i], 9600);` again for same port.
---
### Author:  [@micuat](https://discourse.processing.org/u/micuat)
#### Post date: [March 11, 2021, 11:21pm UTC](https://discourse.processing.org/t/loop-through-serial-ports/28442/4 "2021-03-11T23:21:00Z")
oh. In that case why wouldn’t you keep the already-opened port variable and use it later?
---
### Author:  [@glv](https://discourse.processing.org/u/glv)
#### Post date: [March 15, 2021, 2:23am UTC](https://discourse.processing.org/t/loop-through-serial-ports/28442/5 "2021-03-15T02:23:07Z")
> [@Konstanitn](#):
>
> For my understanding there should be a command like “close.myPort”.
It is here:
_[Serial / Libraries / Processing.org](https://processing.org/reference/libraries/serial/Serial.html)_
`:)`