[SOLVED] Bash shell issuing commands to the process it starts

Rooksu · 07-20-2015, 07:49 AM

Hello!

I have a shell script to start Minecraft. It works great, but I want to be able to send commands to Minecraft from the shell script. For example:

Code:

#!/bin/sh

java -Xms512M -Xmx4096M -XX:MaxPermSize=256M -jar minecraft_server.1.8.7.jar
sleep 10
echo "say This is a test.\r"

The java process starts, but it never gets to the echo. Is there a way to accomplish this? Do I need to start a second script and grab the PID of the java process? Something to do with screens? I've tried a few different things but can't for the life of me figure out where to go from here.

schneidz · 07-20-2015, 08:05 AM

you can background the first command like this:

Code:

#!/bin/sh

java -Xms512M -Xmx4096M -XX:MaxPermSize=256M -jar minecraft_server.1.8.7.jar &
sleep 10
echo "say This is a test.\r"

but not sure if the minecraft server is written to take commands in that fashion.

rtmistler · 07-20-2015, 10:10 AM

Do you know how to send commands to Minecraft? Or that Minecraft would be listening or capable of accepting messages?

The echo would work once you put java in the background as shown, but I don't know whether or not the Minecraft game itself would accept messages if the intent is to send external messages into that applet.

Rooksu · 07-20-2015, 09:06 PM

I know Minecraft can accept commands from shell. Here's a github repo of a web interface that uses shell to issue Minecraft commands: https://github.com/Thue/rfwadmin

I'm trying to dissect it right now. The separate threading with & worked, but as you pointed out the echo wasn't accepted by Minecraft.

berndbausch · 07-20-2015, 11:12 PM

Quote:

Originally Posted by Rooksu

I know Minecraft can accept commands from shell. Here's a github repo of a web interface that uses shell to issue Minecraft commands: https://github.com/Thue/rfwadmin

I'm trying to dissect it right now. The separate threading with & worked, but as you pointed out the echo wasn't accepted by Minecraft.

The echo goes to the standard output of your shell script. Since minecraft is not reading from the standard output, it doesn't receive the echo.

minecraft might read from some IO channel. You have to find out what that channel is. Next step figuring out how to write to it.

rtmistler · 07-21-2015, 07:17 AM

Actually echo might be exactly what would work for you. For instance if you wished to send a character over a serial connection, such as /dev/ttyS0, you could choose to do:

Code:

echo "hi there" > /dev/ttyS0

and then this would be sent out via that serial connection. Therefore if there were a named pipe where Minecraft accepts these commands, echo and the output redirector would do the job. Similarly there are things like /proc or /sys resource files where if you need to change a setting, the resource is read-only. Something like the CPU speed adjust, stuff like that. You would echo a ONE or a ZERO to the file, but not be able to read it back, however it would institute a change in the controls of the system.

Rooksu · 07-22-2015, 06:06 AM

Turns out I was making this harder than it needs to be. Minecraft implemented rcon, so I can communicate with the server without a shell script: https://github.com/thedudeguy/PHP-Minecraft-Rcon

In case someone finds this thread on Google and really does want to use shell scripting, I also got shell working with tmux. If you start the server using tmux (tmux new -a minecraft), you can control it with a shell script like this:

Code:

#!/bin/bash
tmux send-keys -t minecraft "say Hello World!" Enter