how to convert bash script to C++ using boost::iostreams - c++

Question

I'm trying to convert the following bash code into C++ using boost::iostreams:
#!/usr/bin/bash
(
gzip -cd file1.ext.gz
cat file2.ext
) | grep '^regex' # or sed 's/search/replace/'
I can open a file and decompress it:
std::ifstream s("file.ext.gz", std::ios_base::in | std::ios_base::binary);
boost::iostreams::filtering_istreambuf in;
in.push(boost::iostreams::gzip_decompressor());
in.push(s);
Then open an uncompressed file:
std::ifstream s2("file.ext", std::ios_base::in | std::ios_base::binary);
Now I'm a bit stuck, so here are my questions:
1) What's the boost::iostreams solution to concat the two streams?
2) How to output the result through a regex filter to emulate grep/sed?
As a result I'd like to have a an istream that i can copy to cout:
boost::iostream::copy(result, std::cout);
UPDATE complete solution using Hamigaki's concatenate:
/*
* convert the following bash script into C++
*
* #!/bin/bash
* (
* gzip -cd file1.ext.gz
* cat file2.ext
* ) | grep '^filter' | 'sed s/search/replace/g'
*
*/
#include <iostream>
#include <boost/bind.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/device/file.hpp>
#include <boost/iostreams/filter/gzip.hpp>
#include <boost/iostreams/filter/regex.hpp>
#include <boost/iostreams/filter/grep.hpp>
#include <boost/iostreams/copy.hpp>
// http://hamigaki.sourceforge.jp/hamigaki/iostreams/concatenate.hpp
#include "concatenate.hpp"
namespace io = boost::iostreams;
int main(int argc, char const* argv[])
{
io::file_source file1("file1.ext.gz");
io::file_source file2("file2.ext");
io::gzip_decompressor gzip;
io::regex_filter sed(boost::regex("search"), "replace");
io::grep_filter grep(boost::regex("^filter"));
io::filtering_istreambuf in1(gzip | file1);
io::filtering_istreambuf in2(file2);
io::filtering_istreambuf combined(sed | grep |
hamigaki::iostreams::concatenate(
boost::ref(in1),
boost::ref(in2)
)
);
io::copy(combined, std::cout);
return 0;
}

Answer 1

1) I don't know if there's anything built into boost, but this class seems to be exactly what you want: http://hamigaki.sourceforge.jp/hamigaki/iostreams/concatenate.hpp
The catch here is that it expects CopyConstructible devices to concatenate and Chains seem to not be CopyConstructible. However, we can easily work around that using boost::ref. This code does (almost) what I understood you're asking:
int main(int argc, char const* argv[])
{
boost::iostreams::filtering_istreambuf in;
boost::regex regex("search");
boost::iostreams::regex_filter rf(regex, "replace");
in.push(rf);
boost::iostreams::file_source file1(argv[1]);
in.push(file1);
boost::iostreams::file_source file2(argv[2]);
boost::iostreams::copy(hamigaki::iostreams::concatenate(boost::ref(in), file2), std::cout);
return 0;
}
I just used the regex filter instead of gzip, for testing.
2) boost::iostreams has a regex filter: http://www.boost.org/doc/libs/1_45_0/libs/iostreams/doc/classes/regex_filter.html
EDIT: You seem to have this working, now.

Answer 2

1) Not available in boost
Hamigakis's concatenate sounds interesting, but I couldn't figure out how to use it to combine two boost::iostreams::chains. The code mentions it's meant for "concatenation of devices", so it might not be usable for chains. Please correct me if I'm wrong.
EDIT: updated my question with the complete solution.
2a) grep behavior (filter):
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/filter/grep.hpp>
boost::iostreams::filtering_istreambuf in;
boost::regex regex("^search")
boost::iostreams::grep_filter grep(regex);
in.push(grep);
2b) sed behavior (search/replace):
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/filter/regex.hpp>
struct formatter {
std::string operator()(const boost::match_results<const char*>& match)
{
return str(boost::format("%s | %s") % match[2] % match[1]);
}
};
boost::iostreams::filtering_istreambuf in;
boost::regex regex("^([a-z]+) ([0-9]+)");
boost::iostreams::regex_filter sed(regex, formatter());
in.push(sed);