Getting Started

Julia installation is straightforward, whether using precompiled binaries or compiling from source. Download and install Julia by following the instructions at http://julialang.org/downloads/.

The easiest way to learn and experiment with Julia is by starting an interactive session (also known as a read-eval-print loop or “repl”):

$ julia
               _
   _       _ _(_)_     |
  (_)     | (_) (_)    |  A fresh approach to technical computing.
   _ _   _| |_  __ _   |
  | | | | | | |/ _` |  |  Version 0 (pre-release)
  | | |_| | | | (_| |  |  Commit 61847c5aa7 (2011-08-20 06:11:31)*
 _/ |\__'_|_|_|\__'_|  |
|__/                   |

julia> 1 + 2
3

julia> ans
3

To exit the interactive session, type ^D — the control key together with the d key or type quit(). When run in interactive mode, julia displays a banner and prompts the user for input. Once the user has entered a complete expression, such as 1 + 2, and hits enter, the interactive session evaluates the expression and shows its value. If an expression is entered into an interactive session with a trailing semicolon, its value is not shown. The variable ans is bound to the value of the last evaluated expression whether it is shown or not. The ans variable is only bound in interactive sessions, not when Julia code is run in other ways.

To evaluate expressions written in a source file file.jl, write include("file.jl").

To run code in a file non-interactively, you can give it as the first argument to the julia command:

$ julia script.jl arg1 arg2...

As the example implies, the following command-line arguments to julia are taken as command-line arguments to the program script.jl, passed in the global constant ARGS. ARGS is also set when script code is given using the -e option on the command line (see the julia help output below). For example, to just print the arguments given to a script, you could do this:

$ julia -e 'for x in ARGS; println(x); end' foo bar
foo
bar

Or you could put that code into a script and run it:

$ echo 'for x in ARGS; println(x); end' > script.jl
$ julia script.jl foo bar
foo
bar

Julia can be started in parallel mode with either the -p or the --machinefile options. -p n will launch an additional n worker processes, while --machinefile file will launch a worker for each line in file file. The machines defined in file must be accessible via a passwordless ssh login, with Julia installed at the same location as the current host. Each machine definition takes the form [user@]host[:port] [bind_addr] . user defaults to current user, port to the standard ssh port. Optionally, in case of multi-homed hosts, bind_addr may be used to explicitly specify an interface.

If you have code that you want executed whenever julia is run, you can put it in ~\.juliarc.jl:

$ echo 'println("Greetings! 你好! 안녕하세요?")' > ~/.juliarc.jl
$ julia
Greetings! 你好! 안녕하세요?

...

There are various ways to run Julia code and provide options, similar to those available for the perl and ruby programs:

julia [options] [program] [args...]
 -v --version             Display version information
 -h --help                Print this message
 -q --quiet               Quiet startup without banner
 -H --home=<dir>          Load files relative to <dir>
 -T --tab=<size>          Set REPL tab width to <size>

 -e --eval=<expr>         Evaluate <expr>
 -E --print=<expr>        Evaluate and show <expr>
 -P --post-boot=<expr>    Evaluate <expr> right after boot
 -L --load=file           Load <file> right after boot on all processors
 -J --sysimage=file       Start up with the given system image file

 -p n                     Run n local processes
 --machinefile file       Run processes on hosts listed in file

 --no-history             Don't load or save history
 -f --no-startup          Don't load ~/.juliarc.jl
 -F                       Load ~/.juliarc.jl, then handle remaining inputs
 --color=yes|no           Enable or disable color text

 --check-bounds=yes|no    Emit bounds checks always or never (ignoring declarations)