SplitGemini/NoShell

C++ library to easily start subprocesses and pipelines of commands

NoShell library

Overview

The NoShell C++11 library allows to easily starts sub-process with a syntax similar to the shell while not using the shell. It like using the "system()", "popen()", or "spawn()" calls, but easier to use and features similar to the shell.

For example, the following code will run the "grep" command and setup the stream is to read from its standard out.

noshell::istream is;
noshell::Exit e = "grep"_C("-c", "/proc/cpuinfo") | is;

int ncpu;
is >> ncpu;

Now ncpu contains the number of CPUs on your Linux machine. NoShell allows to create pipelines of commands as well, and do redirections (with '<', '>', '>>'), like in the shell. For example, the following shell code:

grep < /proc/cpuinfo | wc -l > ncpus

would be done with NoShell like this:

noshell::Exit e = "grep"_C() < "/proc/cpuinfo" | "wc"_C("-l") > "ncpus";

Note that in the last example, the shell /bin/sh was not used. The redirection of the standard output of grep to the standard input of wc and the standard output of wc to the file "ncpus" is done by the NoShell library itself.

For more documentation and examples, see the doc directory.

Why such a library?

Using a shell to interpret the command passed to "system()", "popen()", or equivalent, is full of problems. The shell has a very complex syntax and the parsing of a command from a string brings security issues and problems with escaping (e.g. spaces in paths, special characters, etc.).

Starting sub-process with fork()/exec() or spawn(), and making the redirections with pipe()/dup() is not so easy and takes a lot of boilerplate code. It is easy to get it wrong and leak resources (file descriptors, memory). NoShell makes all of this simple and convenient, and does not leak resources.

NoShell brings some of the functionality of a shell (running multiple process in a pipeline with input/output redirections) without its problems: the strings are not interpreted and passed directly as arguments to the exec call.

Installation

For installation, use autoconf/automake:

autoreconf -i
./configure
make
sudo make install

At this point, this library has only been tested on Linux, with g++ version 4.7 or newer and clang++ version 3.2.

CMake

Alternatively, you can use CMake to build the library:

mkdir build
cmake -S . -B build
cmake --build build
sudo cmake --install build

Run the tests with:

cd build && ctest

Using the library

Add the following to your make file:

CXXFLAGS = $(shell pkg-config --cflags noshell)
LDFLAGS = $(shell pkg-config --libs noshell)

CMake

Add the following to your CMakeLists.txt:

find_package(noshell REQUIRED)

# link shared library
target_link_libraries(mytarget noshell::noshell)

# link static library
target_link_libraries(mytarget noshell::noshell-static)