Abstract

The bash shell utility mkdir is a tool used to create directories in most POSIX environments. I thought it would be fun to implement such functionality from C++ and maybe forge in some of my own features in the future. I will be using the C++ library Boost to handle the command line options and the Standard Template Libary (std) to work work with the filesystem. I would appreciate some sustains, nays, and comments on the 50 so lines of code I have written.

Code

mkdir.cpp

#include <boost/program_options.hpp>
namespace po = boost::program_options;

#include <filesystem>
#include <iostream>
#include <string.h>
#include <string>
#include <vector>

// Define the LOG() macro in order to be able to add
// a logger in the future without too much refactoring
//#define LOG(x) BOOST_LOG_TRIVIAL(x)
#define LOG(x) std::cout

int main(int argc, char **argv) {
    // Declare the supported options.
    po::options_description desc("Allowed options");
    desc.add_options()
            ("help,h",                       "produce help message")
            ("parents,p", po::bool_switch(), "no error if existing, make parent directories as needed")
            ("verbose,v", po::bool_switch(), "print a message for each created directory");

    const po::parsed_options parsed = po::command_line_parser(argc, argv)
            .options(desc).allow_unregistered().run();
    const std::vector<std::string> unrecognized =
            collect_unrecognized(parsed.options, po::include_positional);
    po::variables_map vm;
    po::store(parsed, vm);
    po::notify(vm);

    for (const auto &opt : unrecognized) {
        if (opt[0] == '-') {
            LOG(error) << "Unknown option '" << opt << "'\n";
            return 1;
        }
    }
    if (vm.count("help") || argc <= 1) {
        LOG(info) << desc;
        return 1;
    }
    std::error_code ec;
    for (const auto &dir_name : unrecognized) {
        auto path = std::filesystem::absolute(std::filesystem::path(dir_name));
        if (vm["parents"].as<bool>())
            std::filesystem::create_directories(path, ec);
        else
            std::filesystem::create_directory(path, ec);
        if (errno) {
            LOG(error) << "Cannot create directory '" << dir_name
                       << "': " << strerror(errno) << '\n';
            errno = 0;
        } else {
            LOG(info) << "Created directory '" << dir_name << "'\n";
        }
    }
    return 0;
}

Try it!

In order to compile this utility the following packages are needed:

sudo apt install build-essential libboost-program-options-dev

Then you can compile mkdir.cpp with:

g++ mkdir.cpp -o mkdir -lboost_program_options -std=c++2a

Then you can test it out with:

./mkdir <options> <directory names>