Book Image

Julia 1.0 Programming - Second Edition

By : Ivo Balbaert
Book Image

Julia 1.0 Programming - Second Edition

By: Ivo Balbaert

Overview of this book

The release of Julia 1.0 is now ready to change the technical world by combining the high productivity and ease of use of Python and R with the lightning-fast speed of C++. Julia 1.0 programming gives you a head start in tackling your numerical and data problems. You will begin by learning how to set up a running Julia platform, before exploring its various built-in types. With the help of practical examples, this book walks you through two important collection types: arrays and matrices. In addition to this, you will be taken through how type conversions and promotions work. In the course of the book, you will be introduced to the homo-iconicity and metaprogramming concepts in Julia. You will understand how Julia provides different ways to interact with an operating system, as well as other languages, and then you'll discover what macros are. Once you have grasped the basics, you’ll study what makes Julia suitable for numerical and scientific computing, and learn about the features provided by Julia. By the end of this book, you will also have learned how to run external programs. This book covers all you need to know about Julia in order to leverage its high speed and efficiency for your applications.
Table of Contents (17 chapters)
Title Page
Copyright and Credits
Packt Upsell

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 1.0.0. (The versioninfo()function in REPL is more detailed, and the VERSION constant only gives you the version number: v"1.0.0"). An option that lets you evaluate expressions on the command line itself is -e, for example:

julia -e 'a = 6 * 7;

The preceding commands print out 42 (this also works in a PowerShell window on Windows, but in an ordinary Windows Command Prompt, use " instead of the ' character).

Some other options that are useful for parallel processing will be discussed in Chapter 9, Running External Programs. Typejulia -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, which contains the following:

for arg in ARGS 

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

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

Sometimes, it can be useful to know when code is executed interactively in the REPL, or when started up with the Julia VM with the julia command. This can be tested with the isinteractive() function. The isinteractive.jl script contains the following code:

println("Is this interactive? $(isinteractive())")

If you start this up in the REPL with include("isinteractive.jl"), the output will be Is this interactive? true.

When started up in a Terminal window as julia isinteractive.jl, the output is Is this interactive? false.


You can download the example code files from your account at for all the Packt Publishing books you have purchased. If you purchased this book elsewhere, you can visit