configurable python versions, account for virtualenv bug

run_linux.sh

@@ -1,5 +1,9 @@
 #!/bin/bash
 
+PYTHON="python3.9" # python binary to use
+
+$PYTHON -V || exit
+
 set -eu
 
 if [ ! -d "mosfet" ]
@@ -11,7 +15,7 @@ fi
 if ! command -v virtualenv &> /dev/null
 then
 	echo "virtualenv could not be found, please install with:"
-	echo "sudo apt install python3-virtualenv"
+	echo "sudo apt install virtualenv"
 	exit
 fi
 
@@ -58,13 +62,16 @@ then
 	rm mcdata.zip
 fi
 
+# https://github.com/pypa/virtualenv/issues/1029
+PS1=${PS1:-}
+
 # create virtual environment
 
 if [ ! -d "env" ] 
 then
 	echo "Installing Python requirements..."
 
-	virtualenv -p python3 env
+	virtualenv -p ${PYTHON} env
 	source env/bin/activate
 	pip install -r requirements.txt
 else
@@ -73,4 +80,4 @@ fi
 
 echo "Running bot..."
 
-python main.py
+${PYTHON} main.py