On Mon, Nov 03, 2014 at 02:32:25PM -0500, Greg Reagle wrote: > I just had a thought that might be of interest to fans of the suckless > philosophy. > > It occurred to me that environment variables can be used to configure a > program, instead of programming in a parser or extension language into a > program. Are there any reasons not to just use environment variables? > Then a rc file could just be a shell script that sets environment > variables. Do you know of any programs that do this? I assume there > are disadvantages, but what?
I personally prefer a short set of environment variables. There is however, some sense in having environment variables that have well-defined semantics across multiple programs. One such example is the http_proxy environment variable. The environment is also of limited size. I think POSIX guarantees a space of about 2kB iirc for environment variables. Tools like xargs(1) need to take this into account and make sure the invoked program will be able to access the environment if necessary. An unreasonable large environment will be capped. This approach also does not scale in general as people will start naming variables differently and possibly result in collisions. A small set of environment variables also helps diagnosing issues, as you can rule out the environment quickly. For run-time configuration I'd opt for command line options or if that is not enough, I'd go for a simple configuration file. There are legitimate cases where config.h is simply not enough or not applicable. Think of a long running daemon where it is not acceptable to restart it. scron[0] for example which is a simple cron daemon does not use config.h but rather parses a crontab file.
