Startup options and Julia scripts

Without any options, the julia command starts up the REPL environment. A useful option to check your environment is julia –v. This shows Julia's version, for example, julia-version 0.3.2+2. (The versioninfo()function in REPL is more detailed, the VERSION constant gives you only the version number: v"0.3.2+2"). An option that lets you evaluate expressions on the command line itself is –e, for example:

 julia -e 'a = 6 * 7;
 println(a)'

The preceding commands print out 42 (on Windows, use " instead of the ' character).

Some other options useful for parallel processing will be discussed in Chapter 9, Running External Programs. Type julia –h for a list of all options.

A script.jl file with Julia source code can be started from the command line with the following command:

julia script.jl arg1 arg2 arg3

Here arg1, arg2, and arg3 are optional arguments to be used in the script's code. They are available from the global constant ARGS. Take a look at the args.jl file as follows:

for arg in ARGS
  println(arg)
end

The julia args.jl 1 Dart C command prints out 1, Dart, and C on consecutive lines.

A script file also can execute other source files by including them in the REPL; for example, main.jl contains include("hello.jl") that will execute the code from hello.jl when called with julia main.jl.