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---
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title: "How to use tmux to send and receive things from your Minecraft server"
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layout: post
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---
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So recently I had problem.
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I run a Minecraft server on a big Linux computer I have running in my room.
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Now, as a system administrator it is very helpful to be able to run some simple commands without needing to login with my key, password, TFA, etc.
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It is, frankly, a lot of work.
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Especially when I really just want to be playing games but I just need to check something quickly.
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So for simple things like finding out of the network, CPU, memory or disk usage is my bottleneck, I wrote this really nifty script to connect the world of Minecraft and the Linux shell.
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My completed solution for what I needed can be found at [https://github.com/TTWNO/termcraft](https://github.com/TTWNO/termcraft/).
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If you want some of the implementation details, stick around.
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## Solution
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So to solve this interesting problem, I decided to use `tmux`.
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`tmux` is a **t**terminal **mu**ltiple**x**er.
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This allows you to run a terminal session, then detach fromc it while it still runs in the background.
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This is very valuable when running command line applications that need to have an active console connection, like a Minecraft server.
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So first I looked at the `tmux` command `send-keys`.
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#### `send-keys`
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`send-keys` allows you to send text, and key presses to a `tmux` session.
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Now assuming this `tmux` session is attached to a Minecraft server,
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there is no reason you could not run a command like this:
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<pre class="terminal">
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$ tmux send-keys "tell @a This is a Test" Enter
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</pre>
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This will send the text "tell @a This is a Test" to the Minecraft server.
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Then, it will hit the newline character, this will execute the command.
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So now we can send information to the server and have it tell the users something.
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But how do we get information about who is typing what in the Minecraft chat?
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### `tmux`'s `capture-pane` is painful
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So in the manual page for `tmux` I can see a section recorded below for options I can give to the `capture-pane` subcommand.
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<pre class="terminal">
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-S and -E specify the starting and ending line numbers,
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zero is the first line of the visible pane and negative
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numbers are lines in the history. ‘-’ to -S is the start
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of the history and to -E the end of the visible pane. The
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default is to capture only the visible contents of the pane.
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</pre>
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What it seems to be saying is I can start at line `-S n` and end at line `-E n`.
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Negative numbers start from the bottom, so *in theory* I can do the following: `tmux capture-pane -S -1` should capture only the last line, because I'm starting from the last line. Right?
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No. It just doesn't work. Negative numbers do *not* work with the `tmux capture-pane` subcommand.
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So I did some simple UNIX piping, like so, to get just the last thing in the chat.
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<pre class="terminal">
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$ tmux capture-pane -p -t steve | tail -n1
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[SERVER] [ExtraDebuggingInfoHere]: <TaterTheTot> MY_MESSAGE
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</pre>
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TaterTheTot is my Minecraft username :)
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`-p` prints the result to the terminal/stdout.
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`steve` is the name of the tmux session I'm trying to pull form.
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So that's done! Beauty!
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Now that we have that, how can we extract the username and the message from the latest line?
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### `grep`
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`grep` is a command to find patterns of text.
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`grep` has an option to only show a matching pattern of text.
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This option is `-o`.
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Let's see how we can use this in conjunction with our latest line of server output to get our results.
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<pre class="terminal">
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$ echo "[DEBUG] [SERVER] blah blah: <TaterTheTot> MY_MESAGE" | grep -o "<.*>"
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<TaterTheTot>
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</pre>
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Now, that's my name with the < and > attached. Not bad!
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We can use the `sed` command to clean it up a bit.
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The syntax is like so: `select/somepattern/replacewith/global`
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So the following command is: `s/[<>]//g`
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Select any characters that are either < or >.
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Replace with nothing.
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Do so globally (as in, don't stop after you replace only one character).
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Take two!
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<pre class="terminal">
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$ echo "[DEBUG] [SERVER] blah blah: <TaterTheTot> MY_MESAGE" | grep -o "<.*>" | sed 's/[<>]//g'
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TaterTheTot
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</pre>
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Beautiful!
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Now what about that pesky message?
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### more `grep`; more `sed`
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Simple: capture everything after the >. Leaving the user's message entirely in tact.
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<pre class="terminal">
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$ echo "[DEBUG] [SERVER] blah blah: <TaterTheTot> MY_MESAGE" | grep -o ">.*$" | sed 's/> //'
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MY_MESSAGE
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</pre>
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So now we have a way to get the username of someone typing in the Minecraft server chat.
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We have a way to find out what they said.
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And, we have a way to respond.
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You can imagine how these might go together for your own use case.
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### Conclusion
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This shows some pretty fun stuff you can do with a few simple Linux commands and a Minecraft server.
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I hope you learned something and found my explanations not horrific haha!
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Remember to checkout the git repository to see what I did with it: [https://github.com/TTWNO/termcraft](https://github.com/TTWNO/termcraft).
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Happy hacking!
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