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”) by double-clicking the Julia executable or running julia from the command line:

$ julia
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.0-dev+2440 (2016-02-01 02:22 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit 2bb94d6 (11 days old master)
|__/                   |  x86_64-apple-darwin13.1.0

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:

$juliascript.jlarg1arg2...

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. The name of the script itself is passed in as the global PROGRAM_FILE. Note that ARGS is also set when script code is given using the -e option on the command line (see the julia help output below) but PROGRAM_FILE will be empty. For example, to just print the arguments given to a script, you could do this:

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

foo
bar

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

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

The -- delimiter can be used to separate command-line args to the scriptfile from args to Julia:

$julia--color=yes-O--foo.jlarg1arg2..

Julia can be started in parallel mode with either the -p or the --machinefile options. -pn will launch an additional n worker processes, while --machinefilefile 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 [count*][user@]host[:port][bind_addr[:port]] . user defaults to current user, port to the standard ssh port. count is the number of workers to spawn on the node, and defaults to 1. The optional bind-tobind_addr[:port] specifies the ip-address and port that other workers should use to connect to this worker.

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 [switches] -- [programfile] [args...]
 -v, --version             Display version information
 -h, --help                Print this message

 -J, --sysimage <file>     Start up with the given system image file
 --precompiled={yes|no}    Use precompiled code from system image if available
 --compilecache={yes|no}   Enable/disable incremental precompilation of modules
 -H, --home <dir>          Set location of `julia` executable
 --startup-file={yes|no}   Load ~/.juliarc.jl
 --handle-signals={yes|no} Enable or disable Julia's default signal handlers

 -e, --eval <expr>         Evaluate <expr>
 -E, --print <expr>        Evaluate and show <expr>
 -L, --load <file>         Load <file> immediately on all processors

 -p, --procs {N|auto}      Integer value N launches N additional local worker processes
                           "auto" launches as many workers as the number of local cores
 --machinefile <file>      Run processes on hosts listed in <file>

 -i                        Interactive mode; REPL runs and isinteractive() is true
 -q, --quiet               Quiet startup (no banner)
 --color={yes|no}          Enable or disable color text
 --history-file={yes|no}   Load or save history

 --compile={yes|no|all|min}Enable or disable JIT compiler, or request exhaustive compilation
 -C, --cpu-target <target> Limit usage of cpu features up to <target>
 -O, --optimize={0,1,2,3}  Set the optimization level (default 2 if unspecified or 3 if specified as -O)
 --inline={yes|no}         Control whether inlining is permitted (overrides functions declared as @inline)
 --check-bounds={yes|no}   Emit bounds checks always or never (ignoring declarations)
 --math-mode={ieee,fast}   Disallow or enable unsafe floating point optimizations (overrides @fastmath declaration)

 --depwarn={yes|no|error}  Enable or disable syntax and method deprecation warnings ("error" turns warnings into errors)

 --output-o name           Generate an object file (including system image data)
 --output-ji name          Generate a system image data file (.ji)
 --output-bc name          Generate LLVM bitcode (.bc)
 --output-incremental=no   Generate an incremental output file (rather than complete)

 --code-coverage={none|user|all}, --code-coverage
                           Count executions of source lines (omitting setting is equivalent to "user")
 --track-allocation={none|user|all}, --track-allocation
                           Count bytes allocated by each source line