mr-edd.co.uk :: horsing around with the C++ programming language

pexl

On the odd occasion, I've found that I've wanted to capture the output of a particular program. The way you do this natively on UNIX and Windows is very different and in each case, it's bloody fiddly.

So I set out to create a library with a platform neutral interface that allows the creation of external processes and interactions with them.

The latest tag in the mercurial repository is 0.1.0, which is stable but only contains code for UNIX. Subsequent revisions contain experimental Windows code.

Recent activity

Code

Clone the repository using mercurial:

> hg clone http://bitbucket.org/edd/pexl

Or get a zip file of the code.

Quick start

To launch a process in the working directory "." and forward its stdout to std::cout:

#include <pexl/exec.hpp>
#include <iostream>

int main()
{
    const char *args[] = { "ls", "-al" }; // $ ls -al
    return pexl::exec(args, args + 2, ".", pexl::out = std::cout);
}

Perhaps we want to capture the errors in a string. We can forward the child process' stderr to a stringstream:

std::list<std::string> args;
args.push_back("find");
args.push_back("/");
args.push_back("-name");
args.push_back("*.txt");  // $ find / -name *.txt

std::ostringstream errors;
int return_code = pexl::exec(args.begin(), args.end(), ".", 
                             pexl::out = std::cout, pexl::err = errors);

Or perhaps we'd like to feed the child's stdin the contents of an std::ifstream:

using namespace pexl;
std::ifstream childinput("childinput.txt");
int return_code = exec(args.begin(), args.end(), ".", 
                       in = childinput, out = std::cout);

To make interaction with existing code easier, pexl can interact with functors as well as C++ streams, meaning you won't have to write your own streambuffer to read/write data from/to a child process.

Further reading

• The pexl wiki

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