The REPL & Your First Program

Useful: Tab completion (also for Unicode: \alpha<Tab> → α), @doc, apropos("sort"), methods(+), @which 1 + 2, @edit sum([1]), varinfo(), versioninfo().

3.1 REPL modes

default / Backspace Useful: Tab completion (also for Unicode: \alpha<Tab> → α), @doc, apropos("sort"), methods(+), @which 1 + 2, @edit sum([1]), varinfo(), versioninfo().

Revise.jl automatically reloads code changes in a running session — install it and put using Revise in ~/.julia/config/startup.jl.

julia> 1 + 2
3
julia> ans * 10          # `ans` holds the last result
30
help?> println           # documentation
shell> ls                # run a shell command
pkg> add Plots           # install a package
julia> exit()            # or Ctrl+D

3.2 Hello World

A script with a main function and arguments:

Julia 1.11+ also supports function (@main)(args) as an explicit entry point.

println("Hello, World!")

julia hello.jl

function main(args)
    name = isempty(args) ? "World" : args[1]
    println("Hello, $name!")
end

main(ARGS)

3.3 Comments

# Single-line comment
#=
  Multi-line comment
  #= can be nested =#
=#
"""
    myfunc(x)

Docstring placed before a definition.
"""
myfunc(x) = x