CL: Command Line parsing for C++

CL is a C++17 single header library that provides an Embedded Domain Specific Language (EDSL) by exploiting C++ features for command line argument parsing.
No regex, grammars, lexers and parsers required!

Quick Start

#include <cl/cl.h>

int main(int argc, char** argv[]) {
    // Needed later for _p operator
    using namespace cl::string_literals;

    // Set some application info (optional)
    cl::set_program("cl_app");
    cl::set_name("CL Application");
    cl::set_description("CL App Description");
    cl::set_version("1.0");

    // Define options (needed if you use options later)
    cl::Options{
        cl::opt("o1", "opt1", "I'm the option 1"),
        cl::opt("o2", "opt2", "I'm the option 2"),
        cl::opt("o3", "opt3"_o, "I'm the option 3"),
    };

    // Create parsing rules (for options, the short name can also be used)
    cl::Usage{
      cl::cmd("command1", "pos1", *"pos2"_p, --"opt1"_p, *--"opt2"_p),
      cl::cmd("command2", "pos1", "pos2"_p, --"opt1"_p, --"opt2"_p),
      cl::cmd("command3", "pos1", cl::one("val1", "val2", "val3")),
      cl::cmd("command4", "pos1", *cl::one("val1", "val2", "val3"), *--"opt3"_p),
      cl::cmd("command5"_a, "pos1"),
      cl::cmd("command6"_a)
      
    };

    cl::Args args = cl::parse(argc, argv);
    // ... parse 'args'
    return 0;
}

• cl::Options: defines a list of command line options, they are shared between all rules (if you only need positional arguments you can skip this step).
• cl::Usage: this is the most important statement, here we define the rules needed to parse command line arguments (positionals, options, optional arguments, etc)
• String literal operators adds some sugar to the code, here is their meaning:
  • _p creates a cl::Param object (more info below)
    • _a creates an 'any-type' command (more info below)
  • _o create a k=v option, if you don't pass this operator, options are just flags (true/false boolean)
• The operator _p create a cl::Param that overloads some C++ operators, these are their meaning:
  • --"myarg"_p creates a required option.
  • if the * is present the argument/option becomes optional (eg. *"pos"_p, *--"opt"_p)
• The operator _a allows any command to be passed (these rules are quite permissive: add them at the end of usage list)
• cl::one("a", "b", "c", ...): is for positional arguments where only one of the provided values are valid (by adding a * makes this argument optional)

Help is autogenerated, for the sample code above.
NOTE: cl_app --help and cl_app --version are builtin.

CL App 1.0
App Description

Usage:
  cl_app command1 <pos1> [pos2] --opt1 [--opt2]
  cl_app command2 <pos1> <pos2> --opt1 --opt2
  cl_app command3 <pos1> (val1|val2|val3)
  cl_app command4 <pos1> [(val1|val2|val3)] [--opt3=ARG]
  cl_app {command5} <pos1>
  cl_app {command6} <pos1>
  cl_app --version
  cl_app --help

Options:
  -h  --help         Show this screen
  -v  --version      Show version
  -o1 --opt1         I'm the option 1
  -o2 --opt2         I'm the option 2
  -o3 --opt3=ARG     I'm the option 3

Extract argument information (explained)

This part is inspired by docopt.cpp.
Calling cl::parse() function returns a cl::Args object, which is simply an std::unordered_map<std::string_view, cl::Value>
Here are some examples:

Case 1

cl_app called as cl_app command4 val1 val2

opt3 = null
command1 = false
pos1 = "arg1"          # The 1st positional argument for this command
pos2 = null
command2 = false
command3 = false
opt2 = false
val1 = false
val2 = true            # We have selected 'val2' for cl::one() param
val3 = false
command4 = "command4"  # We called this command
command5 = false
command6 = false
help = false
version = false
opt1 = false

Case 2

cl_app called as cl_app command2 arg1 arg2 -o1 --opt2

opt3 = null
command1 = false
pos1 = "arg1"          # The 1st positional argument for this command
pos2 = "arg2"          # The 2nd positional argument for this command
command2 = "command2"  # We called this command
command3 = false
opt2 = true            # opt2 is set
val1 = false
val2 = false
val3 = false
command4 = false
command5 = false
command6 = false
help = false
version = false
opt1 = true            # opt1 is set

Extract argument information (C++ code)

In C++ the code looks like this:

#include <iostream>
#include <cl/cl.h>

int main(int argc, char** argv[]) {
    //... create rules & options

    cl::Args args = cl::parse(argc, argv);

    if(args["command2"]) {
        std::cout << "Called command2" << std::endl;
        std::cout << "Positionals: " << args["pos1"] << ", " << args["pos2"] << std::endl;
        std::cout << "Options: " << args["opt1"] << ", " << args["opt2"] << std::endl;
    }
    else if(args["command4"]) {
        std::cout << "Called command4" << std::endl;
        std::cout << "Positionals: " << args["pos1"] << std::endl;

      if(args["val2"].to_bool() == true)
          std::cout << "Val2 is set" << std::endl;
      else
          std::cout << "Val2 is NOT set" << std::endl;
    }

    return 0;
}