RunC

C++ for scripting

RunC is a simple (and somewhat crude) system that helps you use C++ as a scripting language under Unix.

The basic idea is to use Unix's #! script convention to pass control to the runc programme. The runc programme compiles the script as C++ in to an executable, and then runs the executable. The compiled executable is cached, and recompilation only occurs if the script is modified.

Please note that this is the first release of RunC. It has only been used on one operating system (OpenBSD), so things might not work on other systems.

Download

This release of RunC is available as the file runc-1.tar.gz.

Installing RunC

• Edit makefile so that $(install_bin_dir) is set to the absolute path of a directory in your $PATH that you have write access to. The makefile will put two files into this directory, runc and runc2. For example, on my system, I use install_bin_dir := /home/jules/bin/
• Run make install

The makefile is very simple, but requires GNU make.

Using RunC

Making a C++ source file into a script is simple:

• Make the file executable, e.g. chmod a+x <filename>
• Insert a first line #!/bin/sh <absolute path to runc script>, where <absolute path to runc programme> should be <$(install_bin_dir) from the makefile>/runc.
  For example, on my system, I use a first line #!/bin/sh /home/jules/bin/runc

Other things

More than one source file

RunC is intended for single-file C++ programmes. If you want to use code from a different source file, the simplest way of doing this is to simply #include the other source file.

Note that RunC's date-stamp detection will not force a recopmilation when the other source is changed.

The implementation

Probably the best way of implementing RunC would be to install it as a new shell interpreter. But this requires root priviledges, so instead it works in a different way by passing an intermediate shell script to the shell interpreter, using: #!/bin/sh <absolute path to intermediate shell script>. This intermediate shell script is passed the original shell script's filename followed by any parameters.

So, scripts that use the RunC system have a first line like:

#!/bin/sh <absolute path to runc script>

The runc script simply calls runc2, passing all its arguments. runc2 is a compiled C++ programme which implements the main RunC functionality - the datestamp comparisons, calling the compiler and calling the compiled executable.

The command used to compile scripts can be see in runc2.c++; it calls g++, and uses -x c++ to force the input script to be treated as C++ source.

I've only ever used RunC on OpenBSD 3.1 and 3.2; I don't know whether other OS's /bin/sh's behave in exactly the same way.

Customising build commands

You can get custom control of the build by having a second line looking liks: #!-build <build command>. For example:

#!/bin/sh <absolute path to runc programme>
#!-build g++ -D FOO=bar

When a script is compiled, RunC takes this build command, and appends <input filename> -o <output filename>.

Version and license

This is RunC release 1, 24 Dec 2002.

RunC is Copyright (C) 2002 Julian Smith.
RunC is released under the GNU Public License. Please see http://www.gnu.org/copyleft/gpl.html, or write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

Contacting me

Julian Smith, email: jules@op59.net.