How to run a Scala program via cron? - linux

Question

I wrote a small Scala application. I have 2 classes in one source file including the App trait runner to start the program. It works just fine when I run it in the terminal:
scalac update.scala // compiling
scala update // run it
Now I want to run it with a cron job. For this I edited sudo crontab -e and added this:
*/2 * * * * scala /usr/bin/local/update
and made the script executable but nothing happend so far. I'm not sure how to do it:
Do I have to make a jar file for this?
Do I have to add this before my classes or not?
#!/bin/sh
exec scala -savecompiled $0 $#
!#
Does anyone have some experience with this?
Thanks in advance.

Answer 1

I suspect scala isn't in $PATH where cron can see it.
Try the following in a shell session:
$ which scala
Which should output something like "/opt/scala/2.9.1/bin/scala" or something. Could be in /usr/local, any number of places - java and the unix filesystem don't really play together nicely.
So now you have two options:
Put the folder where scala lives in the system path (This will usually involve editing /etc/profile, but you don't specify the OS so I can't say for sure)
(Easier) Just change the the cron entry to call /full/path/to/scala rather than just "scala"

Answer 2

The scala command expects the name of a compiled runnable object or a file containing a scala script source (or a runnable jar file) as the thing to run.
If you have in update.scala object update extends App (and no package declaration) then after scalac update.scala (which should have produced a bunch of *.class files) scala update is the right thing to run.
If the produced class files are not in the current directory then the -classpath option should be used to tell scala where to find them, as in eg. scala -classpath /usr/bin/local update, if the class files are indeed in /usr/bin/local.
Saying scala /usr/bin/local/update would make sense if the file /usr/bin/local/update (this exact name) contained scala script source (that is more or less a sequence of scala expressions not wrapped in a class or object).