Make post on tmux, grep, sed, and Minecraft

_posts/2020-06-25-tmux-minecraft.md

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+---
+title: "How to use tmux to send and receive things from your Minecraft server"
+layout: post
+---
+
+So recently I had problem.
+I run a Minecraft server on a big Linux computer I have running in my room.
+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.
+It is, frankly, a lot of work.
+Especially when I really just want to be playing games, but something seems to be wrong.
+
+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.
+
+My completed solution for what I needed can be found at [https://github.com/TTWNO/termcraft](https://github.com/TTWNO/termcraft/).
+
+If you want some of the implementation details, stick around.
+
+## Solution
+
+So to solve this interesting problem, I decided to use `tmux`.
+`tmux` is a **t**terminal **mu**ltiple**x**er.
+This allows you to run a terminal session, the leave it while it  still runs in the background.
+
+This is very valuable when running command line applications that need to have an active console connection, like a Minecraft server.
+
+So first I looked at the `tmux` command `send-keys`.
+
+#### `send-keys`
+
+`send-keys` allows you to send text, and key presses to a `tmux` session.
+Now assuming this `tmux` session is attached to a Minecraft server,
+there is no reason you could not run a command like this:
+
+<pre class="terminal">
+$ tmux send-keys "tell @a This is a Test" Enter
+</pre>
+
+This will send the text "tell @a This is a Test" to the Minecraft server.
+Then, it will hit the newline character, this will execute the command.
+
+
+So now we can send information to the server and have it tell the users something.
+
+But how do we get information about who is typing what in the Minecraft chat?
+
+### `tmux`'s `capture-pane` is painful
+
+So in the manual page for `tmux` I can see a section recorded below for options I can give to the `capture-pane` subcommand.
+
+<pre class="terminal">
+  -S and -E specify the starting and ending line numbers,
+  zero is the first line of the visible pane and negative
+  numbers are lines in the history.  ‘-’ to -S is the start
+  of the history and to -E the end of the visible pane.  The
+  default is to capture only the visible contents of the pane.
+</pre>
+
+What it seems to be saying is I can start at line `-S n` and end at line `-E n`.
+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?
+
+No. It just doesn't work. Negative numbers do *not* work with the `tmux capture-pane` subcommand.
+
+So I did some simple UNIX piping, like so, to get just the last thing in the chat.
+`-p` prints the result to the terminal/stdout.
+`steve` is the name of the tmux session I'm trying to pull form.
+
+<pre class="terminal">
+$ tmux capture-pane -p -t steve | tail -n1
+[SERVER] [ExtraDebuggingInfoHere]: &lt;TaterTheTot&gt; MY_MESSAGE
+</pre>
+
+So that's done! Beauty!
+
+So now I have a line which will look something like this:
+
+`[SERVER] [ExtraDebugInfoHere]: <TaterTheTot> MY_MESSAGE`
+
+TaterTheTot is my Minecraft username :)
+
+So, how can we get only the message I wrote, and my username?
+
+### `grep`
+
+`grep` is a command to find patterns of text.
+`grep` has an option to only show a matching pattern of text.
+This option is `-o`.
+
+Let's see how we can use this in conjunction with our latest line of server output to get our results.
+
+<pre class="terminal">
+$ echo "[DEBUG] [SERVER] blah blah: &lt;TaterTheTot&gt; MY_MESAGE" | grep -o "&lt;.&ast;&gt;"
+&lt;TaterTheTot&gt;
+</pre>
+
+Now, that's my name with the &lt; and &gt; attached. Not bad!
+We can use the `sed` command to clean it up a bit.
+
+The syntax is like so: `select/somepattern/replacewith/global`
+
+So the following command is: `s/[<>]//g`
+
+Select any characters that are either &lt; or &gt;.
+Replace with nothing.
+Do so globally (as in, don't stop after you replace only one character).
+
+Take two!
+
+<pre class="terminal">
+$ echo "[DEBUG] [SERVER] blah blah: &lt;TaterTheTot&gt; MY_MESAGE" | grep -o "&lt;.&ast;&gt;" | sed 's/[&lt;&gt;]//g'
+TaterTheTot
+</pre>
+
+Beautiful!
+
+Now what about that pesky message?
+
+### more `grep`; more `sed`
+
+Simple: capture everything after the &gt;. Leaving the user's message entirely in tact.
+
+<pre class="terminal">
+$ echo "[DEBUG] [SERVER] blah blah: &lt;TaterTheTot&gt; MY_MESAGE" | grep -o "&gt;.&ast;$" | sed 's/&gt; //'
+MY_MESSAGE
+</pre>
+
+So now we have a way to get the username of someone typing in the Minecraft server chat.
+We have a way to find out what they said.
+And, we have a way to respond.
+
+You can imagine how these might go together for your own use case.
+
+### Conclusion
+
+This shows some pretty fun stuff you can do with a few simple Linux commands and a Minecraft server.
+
+I hope you learned something and found my explanations not horrific haha!
+
+Remember to checkout the git repository to see what I did with it: [https://github.com/TTWNO/termcraft](https://github.com/TTWNO/termcraft).
+
+Happy hacking!