upd

langs/scala/Dockerfile.user

@@ -3,6 +3,6 @@ RUN yes | ./cs setup
 RUN yes | ./cs install scala:3.8.3 scalac:3.8.3
 RUN rm ./cs
 ENV PATH="${PATH}:/home/user/.local/share/coursier/bin"
-RUN echo "@main def hello() = println('Hello, World!')" > hello.sc
-RUN scala run hello.sc
-RUN rm hello.sc
+RUN echo "@main def hello() = println(\"Hello, World!\")" > hello.scala
+RUN scala run hello.scala
+RUN rm hello.scala

langs/scala/run.sh

@@ -1,4 +1,4 @@
-IN="$(mktemp --suffix .sc)"
+IN="$(mktemp --suffix .scala)"
 
 cat > "$IN"