Scripting with Scala: How to launch an uncompiled script? - scala

Question

Apart from serious performance problems, Scala is a very powerful language. Therefore I am now using it frequently for scripted tasks inside Bash. Is there a way to just execute a *.scala file exactly the way I can do with Python files? As far as I know, Python uses bytecode to execute programs, exactly like the JVM does. However, there is not anything called pythonc (like scalac or javac) I need to call in order to accomplish this. Hence I expect Scala to be able to act in a similar manner.

Answer 1

The scala man page provides some examples on how to run Scala code fragments as if they were a script, for both Windows and non-Windows platforms (below examples copied from the man page):
Unix
#!/bin/sh
exec scala "$0" "$#"
!#
Console.println("Hello, world!")
argv.toList foreach Console.println
Windows
::#!
#echo off
call scala %0 %*
goto :eof
::!#
Console.println("Hello, world!")
argv.toList foreach Console.println
To speed up subsequent runs you can cache the compiled fragment with the -savecompiled option:
#!/bin/sh
exec scala -savecompiled "$0" "$#"
!#
Console.println("Hello, world!")
argv.toList foreach Console.println
Update: as of Scala 2.11 (as noted in this similar answer), you can now just do this on Unix:
#!/usr/bin/env scala
println("Hello, world!")
println(args.mkString(" "))

Answer 2

I don't use python, but in Scala, the most scripty thing I can do is this:
thinkpux:~/proj/mini/forum > echo 'println(" 3 + 4 = " + (3 + 4))' | scala
Welcome to Scala version 2.10.2 (Java HotSpot(TM) Server VM, Java 1.7.0_09).
Type in expressions to have them evaluated.
Type :help for more information.
scala> println(" 3 + 4 = " + (3 + 4))
3 + 4 = 7
scala> thinkpux:~/proj/mini/forum >
However, afterwards, I don't have visual feedback in the bash, so I have to call 'clear'.
But there is no problem in writing a script and executing that:
thinkpux:~/proj/mini/forum > echo 'println(" 3 + 4 = " + (3 + 4))' > print7.scala
thinkpux:~/proj/mini/forum > scala print7.scala
3 + 4 = 7
Then, there aren't issues with the shell.
With an enclosing class, the code wouldn't be executed:
thinkpux:~/proj/mini/forum > echo -e 'class Foo {\nprintln(" 3 + 4 = " + (3 + 4))\n}\n'
class Foo {
println(" 3 + 4 = " + (3 + 4))
}
thinkpux:~/proj/mini/forum > scala Foo.scala
thinkpux:~/proj/mini/forum > cat Foo.scala
class Foo {
println(" 3 + 4 = " + (3 + 4))
}
But with instatiating a class, you can execute code in it, without using the wellknown (hope so) 'main' way:
thinkpux:~/proj/mini/forum > echo -e 'class Foo {\nprintln(" 3 + 4 = " + (3 + 4))\n}\nval foo = new Foo()' > Foo.scala
thinkpux:~/proj/mini/forum > cat Foo.scala
class Foo {
println(" 3 + 4 = " + (3 + 4))
}
val foo = new Foo()
thinkpux:~/proj/mini/forum > scala Foo.scala
3 + 4 = 7