The scala utility runs Scala code using a Java runtime environment. The Scala code to run is specified in one of three ways:
If -howtorun: is left as the default (guess), then the scala command will check whether a file of the specified name exists. If it does, then it will treat it as a script file; if it does not, then it will treat it as the name of an object.
In all three cases, arbitrary scalac options may be specified. The most common option is to specify a classpath with -classpath, but see the scalac(1) page for full details.
If an object is specified to run, then that object must be a top-level Scala object with the specified name. The object must define a method main with the following signature:
The method must return a Unit value, and it must accept a String array as a parameter. All arguments specified on the command line will be passed as arguments to the main method.
If a script file is specified to run, then the file is read and all Scala statements and declarations in the file are processed in order. Any arguments specified will be available via the argsvariable.
Script files may have an optional header that is ignored if present. There are two ways to format the header: either beginning with #! and ending with !#, or beginning with ::#! and ending with ::!#.
Such a header must have each header boundary start at the beginning of a line. Headers can be used to make stand-alone script files, as shown in the examples below.
When running a script or using -e, an already running compilation daemon (fsc) is used, or a new one started on demand. The -nocompdaemon or -nc option can be used to prevent this.
If any compiler options are specified, they must be first in the command line and must be followed by a bare hyphen ("-") character. If no arguments are specified after the optional compiler arguments, then an interactive Scala shell is started. Otherwise, either a script file is run, or a pre-compiled Scala object is run. It is possible to distinguish the last two cases by using an explicit -object or -script flag, but usually the program can guess correctly.
Here are some examples of running Scala code:
Here is a complete Scala script for Unix:
#!/bin/sh exec scala "$0" "$@" !# Console.println("Hello, world!") args.toList foreach Console.println
Here is a complete Scala script for MS Windows:
::#! @echo off call scala %0 %* goto :eof ::!# Console.println("Hello, world!") args.toList foreach Console.println
If you want to use the compilation cache to speed up multiple executions of the script, then add -savecompiled to the scala command:
#!/bin/sh exec scala -savecompiled "$0" "$@" !# Console.println("Hello, world!") args.toList foreach Console.println
The scala command returns a zero exit status if it succeeds. Non zero is returned in case of any error. If a script or top-level object is executed and returns a value, then that return value is passed on to scala.
Report bugs to https://github.com/scala/bug/issues.
This is open-source software, available to you under the Apache License 2.0. See accompanying "copyright" or "LICENSE" file for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.