Command-line Interface
Using arguments inside scripts
When running a script using julia
, you can pass additional arguments to your script:
$ julia script.jl arg1 arg2...
These additional command-line arguments are 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 a Julia expression 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 arguments intended for the script file from arguments intended for Julia:
$ julia --color=yes -O -- script.jl arg1 arg2..
See also Scripting for more information on writing Julia scripts.
The Main.main
entry point
As of Julia, 1.11, Base
exports the macro @main
. This macro expands to the symbol main
, but at the conclusion of executing a script or expression, julia
will attempt to execute Main.main(Base.ARGS)
if such a function Main.main
has been defined and this behavior was opted into by using the @main
macro.
This feature is intended to aid in the unification of compiled and interactive workflows. In compiled workflows, loading the code that defines the main
function may be spatially and temporally separated from the invocation. However, for interactive workflows, the behavior is equivalent to explicitly calling exit(main(ARGS))
at the end of the evaluated script or expression.
The special entry point Main.main
was added in Julia 1.11. For compatibility with prior julia versions, add an explicit @isdefined(var"@main") ? (@main) : exit(main(ARGS))
at the end of your scripts.
To see this feature in action, consider the following definition, which will execute the print function despite there being no explicit call to main
:
$ julia -e '(@main)(args) = println("Hello World!")'
Hello World!
$
Only the main
binding in the Main
module has this behavior and only if the macro @main
was used within the defining module.
For example, using hello
instead of main
will not result in the hello
function executing:
$ julia -e 'hello(args) = println("Hello World!")'
$
and neither will a plain definition of main
:
$ julia -e 'main(args) = println("Hello World!")'
$
However, the opt-in need not occur at definition time:
$ julia -e 'main(args) = println("Hello World!"); @main'
Hello World!
$
The main
binding may be imported from a package. A hello world package defined as
module Hello
export main
(@main)(args) = println("Hello from the package!")
end
may be used as:
$ julia -e 'using Hello'
Hello from the package!
$ julia -e 'import Hello' # N.B.: Execution depends on the binding not whether the package is loaded
$
However, note that the current best practice recommendation is to not mix application and reusable library code in the same package. Helper applications may be distributed as separate packages or as scripts with separate main
entry points in a package's bin
folder.
Parallel mode
Julia can be started in parallel mode with either the -p
or the --machine-file
options. -p n
will launch an additional n
worker processes, while --machine-file file
will launch a worker for each line in file file
. The machines defined in file
must be accessible via a password-less 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-to bind_addr[:port]
specifies the IP address and port that other workers should use to connect to this worker.
Startup file
If you have code that you want executed whenever Julia is run, you can put it in ~/.julia/config/startup.jl
:
$ echo 'println("Greetings! 你好! 안녕하세요?")' > ~/.julia/config/startup.jl
$ julia
Greetings! 你好! 안녕하세요?
...
Note that although you should have a ~/.julia
directory once you've run Julia for the first time, you may need to create the ~/.julia/config
folder and the ~/.julia/config/startup.jl
file if you use it.
To have startup code run only in The Julia REPL (and not when julia
is e.g. run on a script), use atreplinit
in startup.jl
:
atreplinit() do repl
# ...
end
Command-line switches for Julia
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...]
The following is a complete list of command-line switches available when launching julia (a '*' marks the default value, if applicable; settings marked '($)' may trigger package precompilation):
Switch | Description |
---|---|
-v , --version | Display version information |
-h , --help | Print command-line options (this message) |
--help-hidden | Print uncommon options not shown by -h |
--project[={<dir>|@temp|@.}] | Set <dir> as the active project/environment. Or, create a temporary environment with @temp . The default @. option will search through parent directories until a Project.toml or JuliaProject.toml file is found. |
-J , --sysimage <file> | Start up with the given system image file |
-H , --home <dir> | Set location of julia executable |
--startup-file={yes*|no} | Load JULIA_DEPOT_PATH/config/startup.jl ; if JULIA_DEPOT_PATH environment variable is unset, load ~/.julia/config/startup.jl |
--handle-signals={yes*|no} | Enable or disable Julia's default signal handlers |
--sysimage-native-code={yes*|no} | Use native code from system image if available |
--compiled-modules={yes*|no|existing|strict} | Enable or disable incremental precompilation of modules. The existing option allows use of existing compiled modules that were previously precompiled, but disallows creation of new precompile files. The strict option is similar, but will error if no precompile file is found. |
--pkgimages={yes*|no|existing} | Enable or disable usage of native code caching in the form of pkgimages. The existing option allows use of existing pkgimages but disallows creation of new ones |
-e , --eval <expr> | Evaluate <expr> |
-E , --print <expr> | Evaluate <expr> and display the result |
-m , --module <Package> [args] | Run entry point of Package (@main function) with `args' |
-L , --load <file> | Load <file> immediately on all processors |
-t , --threads {auto|N[,auto|M]} | Enable N[+M] threads; N threads are assigned to the default threadpool, and if M is specified, M threads are assigned to the interactive threadpool; auto tries to infer a useful default number of threads to use but the exact behavior might change in the future. Currently sets N to the number of CPUs assigned to this Julia process based on the OS-specific affinity assignment interface if supported (Linux and Windows) or to the number of CPU threads if not supported (MacOS) or if process affinity is not configured, and sets M to 1. |
--gcthreads=N[,M] | Use N threads for the mark phase of GC and M (0 or 1) threads for the concurrent sweeping phase of GC. N is set to the number of compute threads and M is set to 0 if unspecified. |
-p , --procs {N|auto} | Integer value N launches N additional local worker processes; auto launches as many workers as the number of local CPU threads (logical cores) |
--machine-file <file> | Run processes on hosts listed in <file> |
-i , --interactive | Interactive mode; REPL runs and isinteractive() is true |
-q , --quiet | Quiet startup: no banner, suppress REPL warnings |
--banner={yes|no|short|auto*} | Enable or disable startup banner |
--color={yes|no|auto*} | Enable or disable color text |
--history-file={yes*|no} | Load or save history |
--depwarn={yes|no*|error} | Enable or disable syntax and method deprecation warnings (error turns warnings into errors) |
--warn-overwrite={yes|no*} | Enable or disable method overwrite warnings |
--warn-scope={yes*|no} | Enable or disable warning for ambiguous top-level scope |
-C , --cpu-target <target> | Limit usage of CPU features up to <target> ; set to help to see the available options |
-O , --optimize={0|1|2*|3} | Set the optimization level (level is 3 if -O is used without a level) ($) |
--min-optlevel={0*|1|2|3} | Set the lower bound on per-module optimization |
-g , --debug-info={0|1*|2} | Set the level of debug info generation (level is 2 if -g is used without a level) ($) |
--inline={yes|no} | Control whether inlining is permitted, including overriding @inline declarations |
--check-bounds={yes|no|auto*} | Emit bounds checks always, never, or respect @inbounds declarations ($) |
--math-mode={ieee|user*} | Always follow ieee floating point semantics or respect @fastmath declarations |
--polly={yes*|no} | Enable or disable the polyhedral optimizer Polly (overrides @polly declaration) |
--code-coverage[={none*|user|all}] | Count executions of source lines (omitting setting is equivalent to user ) |
--code-coverage=@<path> | Count executions but only in files that fall under the given file path/directory. The @ prefix is required to select this option. A @ with no path will track the current directory. |
--code-coverage=tracefile.info | Append coverage information to the LCOV tracefile (filename supports format tokens). |
--track-allocation[={none*|user|all}] | Count bytes allocated by each source line (omitting setting is equivalent to "user") |
--track-allocation=@<path> | Count bytes but only in files that fall under the given file path/directory. The @ prefix is required to select this option. A @ with no path will track the current directory. |
--bug-report=KIND | Launch a bug report session. It can be used to start a REPL, run a script, or evaluate expressions. It first tries to use BugReporting.jl installed in current environment and falls back to the latest compatible BugReporting.jl if not. For more information, see --bug-report=help . |
--heap-size-hint=<size> | Forces garbage collection if memory usage is higher than the given value. The value may be specified as a number of bytes, optionally in units of KB, MB, GB, or TB, or as a percentage of physical memory with %. |
--compile={yes*|no|all|min} | Enable or disable JIT compiler, or request exhaustive or minimal compilation |
--output-o <name> | Generate an object file (including system image data) |
--output-ji <name> | Generate a system image data file (.ji) |
--strip-metadata | Remove docstrings and source location info from system image |
--strip-ir | Remove IR (intermediate representation) of compiled functions |
--output-unopt-bc <name> | Generate unoptimized LLVM bitcode (.bc) |
--output-bc <name> | Generate LLVM bitcode (.bc) |
--output-asm <name> | Generate an assembly file (.s) |
--output-incremental={yes|no*} | Generate an incremental output file (rather than complete) |
--trace-compile={stderr|name} | Print precompile statements for methods compiled during execution or save to a path |
--trace-compile-timing | If –trace-compile is enabled show how long each took to compile in ms |
--image-codegen | Force generate code in imaging mode |
--permalloc-pkgimg={yes|no*} | Copy the data section of package images into memory |
In Julia 1.0, the default --project=@.
option did not search up from the root directory of a Git repository for the Project.toml
file. From Julia 1.1 forward, it does.