How to send keyboard function keys to SSH server from java code

Question

There is a menu item that gets displayed on the console after the connection of the session. And that menu items have command with F1, F2, F3

String host="myhost.abc.123";
String user="devuser";
String password="dev1234";

Properties config = new Properties();
config.put("StrictHostKeyChecking", "no");
JSch jsch = new JSch();
Session session = null;
ChannelShell channel = null;

session = jsch.getSession(user, host, 22);
session.setPassword(password);
session.setConfig(config);
session.connect();
System.out.println("Connected");

channel = (ChannelShell) session.openChannel("shell");
OutputStream out_s = channel.getOutputStream();
channel.connect();

I want to send the F2 - function key as a hardcoded escape sequence or from the keyboard, to server. Tried below options but I am not getting the next response/output

/* --- code for printing the menu item on the console/screen ---
MENU ITEMS GET PRINTED ON THE CONSOLE
F1 - ADD   F2 - UPDATE   F3 - DELETE      
*/

//Try 1. F2 - ESC[OQ 
out_s.write("\033[OQ".getBytes()); // may require \n or \r to enter the cmd
out_s.flush();

//Try 2. F2 - ESC[12~ 
out_s.write("\033[12~".getBytes()); // may require \n or \r to enter the cmd
out_s.flush();

//Try 3. F2 - \E[12~ 
out_s.write("\\E[12~".getBytes());
out_s.flush();

//Try 4. F2 - 0x71 
out_s.write((byte)0x71); // may require \n or \r to enter the cmd
out_s.flush();

//Try 5. F2 - \ESC[OQ
out_s.write("\\ESC[OQ".getBytes());
out_s.flush();

Donat · Accepted Answer · 2020-10-27 21:14:28Z

1

This worked for me:

out.write("\u001b[12~".getBytes());
out.flush();

On the server I tested by:

read -n 5 key

This reads 5 bytes from standard input without waiting for a return key. Of course, this is only for test. You can do your own processing on the server side.

How to find out what is being sent by a specific key (in bash):

read key

Then type (for example) the F2 key. The terminal should show something like this:

^[[12~

If not, try this command to show the bytes sent to the terminal:

echo $key | cat -t

In the output ^[ stands for the (non printable) escape character. The other characters stand for themselves.

edited Oct 27, 2020 at 21:14

answered Oct 25, 2020 at 17:36

Donat

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3 Comments

Mohit Over a year ago

I did not work out. I tried. Is it related to type of input stream keyboard. VT100 ot something. While debugging, I get in input stream the property ttype=vt100. Do we require any \n or \r ?

Mohit Over a year ago

I tried using echo $key ...... It gives [[12~ on the screen. But how to pass in java inside out.write ? Because "[[12~".getBytes() is not working and also tried \[[12~ and "\u001b\u001b12~".getBytes(). More over ^[[12 also not working.

Donat Over a year ago

I think, your output must be '^[[12~', not '[[12~'. In this case my Java code would be the ok. If it is not working, I suppose the problem must be elsewhere. Maybe the program running in the remote terminal expects something else. Which command did you start on the remote system in this session?

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