Julia is a dynamically typed programming language that focuses on high-level, high-performance computing. It provides a REPL (Read-Eval-Print Loop) environment for interactive use and also allows executing Julia programs and evaluating Julia code from the command line. In this article, we will explore eight different use cases of the Julia command with code examples to demonstrate its versatility and usefulness.

Start a REPL (interactive shell)

Code:

julia

Motivation:

Starting a REPL is the most basic way to interact with Julia. It allows you to experiment with code, evaluate expressions, and get immediate feedback.

Explanation:

This command simply starts a Julia REPL, where you can enter and execute Julia code.

Example Output:

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.6.2 (2021-07-14)
 _/ |\__'_|_|_|\__'_|  |
|__/                   |

julia>

Execute a Julia program and exit

Code:

julia program.jl

Motivation:

The ability to execute Julia programs allows for more extensive and complex scripting. By executing a program and exiting, you can automate specific tasks or run batch processes.

Explanation:

This command runs the Julia program specified by program.jl and then exits.

Example Output:

Hello, World!

Execute a Julia program that takes arguments

Code:

julia program.jl arguments

Motivation:

Some Julia programs require arguments to customize their behavior or provide input data. By passing arguments to a Julia program, you can create more flexible and versatile applications.

Explanation:

This command runs the Julia program specified by program.jl and provides the arguments as command-line arguments.

Example Output:

Hello, John Doe!

Evaluate a string containing Julia code

Code:

julia -e 'julia_code'

Motivation:

The ability to evaluate a string of Julia code from the command line can be useful for quick experimentation or for executing short snippets of code.

Explanation:

This command evaluates the julia_code string as Julia code and prints the result.

Example Output:

42

Evaluate a string of Julia code, passing arguments to it

Code:

julia -e 'for x in ARGS; println(x); end' arguments

Motivation:

In some cases, you may want to evaluate a string of Julia code that relies on command-line arguments. This use case allows you to combine both input parameters and code evaluation.

Explanation:

This command evaluates the for x in ARGS; println(x); end string as Julia code. The arguments are passed as command-line arguments to the evaluated code.

Example Output:

foo
bar
baz

Evaluate an expression and print the result

Code:

julia -E '(1 - cos(pi/4))/2'

Motivation:

Evaluating an expression and printing the result can be handy for quickly calculating values or checking the output of a specific computation.

Explanation:

This command evaluates the (1 - cos(pi/4))/2 expression as Julia code and prints the result.

Example Output:

0.14644660940672627

Start Julia in parallel mode, using N worker processes

Code:

julia -p N

Motivation:

In certain scenarios, parallel computing can significantly improve performance. Starting Julia in parallel mode allows you to distribute work across multiple worker processes.

Explanation:

This command starts Julia in parallel mode, using N worker processes to handle computations.

Example Output:

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.6.2 (2021-07-14)
 _/ |\__'_|_|_|\__'_|  |
|__/                   |

julia> 

Conclusion

The julia command provides various capabilities for interacting with Julia, from starting a REPL for interactive exploration to executing programs and evaluating code from the command line. These different use cases offer flexibility and versatility when working with Julia, allowing you to build complex applications, automate tasks, and experiment with code.