cpp-subprocess

subprocess is a small header-only library that provides convenient C++ API to execute shell commands. It is similar to popen(), as it creates a new process and executes the command by invoking shell. The difference compared to popen() is that stdin, stdout and stderr of the child process are associated to iostream objects which can be accessed by the parent process.

The library uses GNU extension __gnu_cxx::stdio_filebuf to construct iostream objects from file descriptors. It works on gcc and it can work also with clang as long as GNU's C++ standard library is used.

Tutorial

The first example executes ls and print the directory listing of the current working directory into standard out.

#include "subprocess.hpp"

int
main(int argc, char *argv[])
{
    subprocess::popen cmd("ls", {});
    std::cout << cmd.out().rdbuf();

    return 0;
}

The second example executes sort -r and write the contents of inputfile.txt to the standard input of the executed command. It will then read the standard output of the command and print it. The resulting output is the reverse sorted contents of the inputfile.txt.

#include <fstream>
#include "subprocess.hpp"

int
main(int argc, char *argv[])
{
    subprocess::popen cmd("sort", {"-r"});

    std::ifstream file("inputfile.txt");
    std::string line;

    while (std::getline(file, line))
    {
       cmd.in() << line << std::endl;
    }
    cmd.close();

    std::cout << cmd.out().rdbuf();

    return 0;
}

Shell-like pipes can be constructed between output and input of two commands. Following example executes equivalent of cat | sort -r for input containing three lines: "a", "b" and "c". The result read from the output stream contains the input in reversed order.

#include <fstream>
#include "subprocess.hpp"

int
main(int argc, char *argv[])
{
    subprocess::popen sort_cmd("sort", {"-r"});
    subprocess::popen cat_cmd("cat", {}, sort_cmd.in());

    cat_cmd.in() << "a" << std::endl;
    cat_cmd.in() << "b" << std::endl;
    cat_cmd.in() << "c" << std::endl;
    cat_cmd.close();

    std::cout << sort_cmd.out().rdbuf();

    return 0;
}

To write to and read from a subprocess for multiple times, use std::getline() or some other way to read without blocking:

#include <string>
#include "subprocess.hpp"

int
main(int argc, char *argv[])
{
    std::string buf;

    subprocess::popen cat_cmd("cat", {});

    cat_cmd.in() << "a" << std::endl;
    std::getline(cat_cmd.out(), buf);
    std::cout << buf << std::endl;

    cat_cmd.in() << "b" << std::endl;
    std::getline(cat_cmd.out(), buf);
    std::cout << buf << std::endl;

    cat_cmd.in() << "c" << std::endl;
    std::getline(cat_cmd.out(), buf);
    std::cout << buf << std::endl;

    return 0;
}

Installation

The library consists of single file include/subprocess.hpp. Copy the file into your own project or e.g. into /usr/local/include/.

Use -std=c++11 when compiling the code.

Unit test suite depends on Boost Test Library.