Command Line Flags in Julia

Here’s the translation of the Go code to Julia, with explanations in Markdown format suitable for Hugo:

[Command-line flags](https://en.wikipedia.org/wiki/Command-line_interface#Command-line_option) are a common way to specify options for command-line programs. For example, in `wc -l` the `-l` is a command-line flag.

Julia provides the `ArgParse` package for parsing command-line arguments. We'll use this package to implement our example command-line program.

```julia
using ArgParse

function parse_commandline()
    s = ArgParseSettings()

    @add_arg_table s begin
        "--word"
            help = "a string"
            default = "foo"
        "--numb"
            help = "an int"
            arg_type = Int
            default = 42
        "--fork"
            help = "a bool"
            action = :store_true
        "--svar"
            help = "a string var"
            default = "bar"
    end

    return parse_args(s)
end

function main()
    parsed_args = parse_commandline()
    
    println("word: ", parsed_args["word"])
    println("numb: ", parsed_args["numb"])
    println("fork: ", parsed_args["fork"])
    println("svar: ", parsed_args["svar"])
    println("tail: ", join(parsed_args["ARGS"], " "))
end

main()

To experiment with the command-line flags program, save it to a file (e.g., command_line_flags.jl) and run it using the Julia interpreter.

Try out the program by giving it values for all flags:

$ julia command_line_flags.jl --word=opt --numb=7 --fork --svar=flag
word: opt
numb: 7
fork: true
svar: flag
tail:

Note that if you omit flags, they automatically take their default values:

$ julia command_line_flags.jl --word=opt
word: opt
numb: 42
fork: false
svar: bar
tail:

Trailing positional arguments can be provided after any flags:

$ julia command_line_flags.jl --word=opt a1 a2 a3
word: opt
numb: 42
fork: false
svar: bar
tail: a1 a2 a3

The ArgParse package allows flags to appear in any order, even mixed with positional arguments.

Use the -h or --help flag to get automatically generated help text for the command-line program:

$ julia command_line_flags.jl -h
usage: command_line_flags.jl [--word WORD] [--numb NUMB] [--fork]
                             [--svar SVAR] [-h]

optional arguments:
  --word WORD   a string (default: "foo")
  --numb NUMB   an int (type: Int64, default: 42)
  --fork        a bool
  --svar SVAR   a string var (default: "bar")
  -h, --help    show this help message and exit

If you provide a flag that wasn’t specified in the ArgParse setup, the program will print an error message and show the help text.

$ julia command_line_flags.jl --wat
error: unknown option "--wat"
[...]


This translation maintains the structure and explanation of the original Go example, adapting it to use Julia's `ArgParse` package for command-line argument parsing. The functionality is similar, with some differences due to the specifics of Julia and the `ArgParse` package.

Command Line Arguments in Julia

Context in Julia

Learn X By Example

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Command Line Flags in Julia