scala

Section: USER COMMANDS (1)
Updated: April 2007
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NAME

scala - Run code in the Scala 2 language

SYNOPSIS

scala [ <option> ]... [ <torun> <argument>... ]

PARAMETERS

<compiler-option>: Any scalac option. See scalac(1).
-howtorun:<how>: How to execute <torun>, if it is present. Options for <how> are guess (the default), script, jar, and object.
-i <file>: Requests that a file be pre-loaded. It is only meaningful for interactive shells.
-e <string>: Requests that its argument be executed as Scala code.
-savecompiled: Save this compiled version of scripts in order to speed up later executions of the same script. When running a script, save the compiled version in a file with the same name as the script but with an extension of .jar. On subsequent runs of the same script, the pre-compiled .jar file will be used if it is newer than the script file.
-nocompdaemon: Do not use the fsc offline compiler.
-nc: Same as -nocompdaemon.
-Dproperty=value: Set a Java system property. If no value is specified, then the property is set to the empty string.
<torun>: A top-level object or a script file to run.
<argument>: An arguments to pass to <torun>.

DESCRIPTION

The scala utility runs Scala code using a Java runtime environment. The Scala code to run is specified in one of three ways:

1.: With no arguments specified, a Scala shell starts and reads commands interactively.
2.: With -howtorun:object specified, the fully qualified name of a top-level Scala object may be specified. The object should previously have been compiled using scalac(1).
3.: With -howtorun:script specified, a file containing Scala code may be specified.

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:

def main(args: Array[String]): Unit

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 no -classpath option is specified, then scala will add ".", the current directory, to the end of the classpath.

OPTIONS

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.

ENVIRONMENT

JAVACMD: Specify the java command to be used for running the Scala code. Arguments may be specified as part of the environment variable; spaces, quotation marks, etc., will be passed directly to the shell for expansion.
JAVA_HOME: Specify JDK/JRE home directory. This directory is used to locate the java command unless JAVACMD variable set.
JAVA_OPTS: Specify the options to be passed to the java command defined by JAVACMD.
: One might for example configure the memory usage of the JVM with: JAVA_OPTS="-Xmx2G -Xss16M"

EXAMPLES

Here are some examples of running Scala code:

Execute a Scala program generated in the current directory: scala hello.HelloWorld
Execute a Scala program generated in a user-defined directory classes: scala -classpath classes hello.HelloWorld
Execute a Scala program using a user-defined java command: env JAVACMD=/usr/local/bin/cacao scala -classpath classes hello.HelloWorld
Execute a Scala program using JVM options: env JAVACMD=java JAVA_OPTS="-Dmsg=hello -enableassertions" scala -classpath classes hello.HelloWorld

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

EXIT STATUS

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.

AUTHOR

Written by Martin Odersky and other members of the Scala team.

REPORTING BUGS

Report bugs to https://github.com/scala/bug/issues.

COPYRIGHT

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.