Introduction to Julia
Running Julia code
There are several ways to write and run Julia code:
The Julia REPL (read-evaluate-print-loop)
Fire it up by typing julia (or the full path to the executable) in the command-line interface (CLI). The REPL itself comes with four distinct modes:
Julia mode: This is the default mode when we start Julia. The prompt starts with
julia>. Here we may type Julia expressions which get evaluated when pressing enter. The resulting output will be presented immediately after evaluation.
julia> 1 + 1
2
julia>Package mode: We can switch to this mode by typing
]. The prompt will change to(@v1.8) pkg>(version number depends on the installation). Here we can directly interact with the package manager to add or update packages. To get a complete list of possibilities type?
(@v1.8) pkg> ?
Welcome to the Pkg REPL-mode. To return to the julia> prompt, either press backspace when the input line is empty or press Ctrl+C.
Full documentation available at https://pkgdocs.julialang.org/
Synopsis
pkg> cmd [opts] [args]
Multiple commands can be given on the same line by interleaving a ; between the commands. Some commands have an alias, indicated below.
Commands
activate: set the primary environment the package manager manipulates
add: add packages to project
build: run the build script for packages
compat: edit compat entries in the current Project and re-resolve
develop, dev: clone the full package repo locally for development
free: undoes a pin, develop, or stops tracking a repo
gc: garbage collect packages not used for a significant time
generate: generate files for a new project
help, ?: show this message
instantiate: downloads all the dependencies for the project
pin: pins the version of packages
precompile: precompile all the project dependencies
redo: redo the latest change to the active project
remove, rm: remove packages from project or manifest
resolve: resolves to update the manifest from changes in dependencies of developed packages
status, st: summarize contents of and changes to environment
test: run tests for packages
undo: undo the latest change to the active project
update, up: update packages in manifest
registry add: add package registries
registry remove, rm: remove package registries
registry status, st: information about installed registries
registry update, up: update package registries
(@v1.8) pkg>Help mode: Type
?and the prompt will change tohelp?>. Julia prints the help and documentation for everything we ask for (related to Julia).
help?> +
search: +
+(x, y...)
Addition operator. x+y+z+... calls this function with all arguments, i.e. +(x, y, z, ...).
Examples
≡≡≡≡≡≡≡≡≡≡
julia> 1 + 20 + 4
25
julia> +(1, 20, 4)
25
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
dt::Date + t::Time -> DateTime
The addition of a Date with a Time produces a DateTime. The hour, minute, second, and millisecond parts of the Time are used along with the year, month, and day of the Date to create the new DateTime. Non-zero microseconds
or nanoseconds in the Time type will result in an InexactError being thrown.
julia>Shell mode: We can switch to this mode by typing
;and the prompt will change toshell>. Now we are in the usual shell and are able to type any command we want to evaluate.
shell> pwd
/home/user/ws22_julia_ulg
shell>Note that all these modes use Julia functions under the hood. For example ?+ is equivalent to Base.Docs.doc(+). All package functions can be called inside Julia using import Pkg and, e.g., Pkg.update().
VS Code
See Julia and VS Code.
Other interactive development environments
A lot of other IDEs or text editors like Jupyter, Sublime Text, Nano, vim and many more can also be used in connection with Julia. Some integrate the evaluation inside the editor. For others we will have to do this in the CLI. Note that we can always run Julia code from CLI by typing julia myProgram.jl.
If we are just exploring of what Julia is capable of or need some help regarding specific Julia functionality the REPL is very useful. However, once we want to run a program or repeat a process we switch to running code from a file. In the REPL we can use the arrow keys up and down to navigate through previous calls (if our CLI allows it).
Additional sources
If you are already familiar with another programming language it might be worth visiting Noteworthy Differences from other Languages from the Julia documentation.