UNIX for Dummies Questions & Answers

Is there a way to make a permanent pseudo-file, whose contents may dynamically change? I'm thinking of something like an SQL view here. I've been trying to do this with pipes, but I haven't been able to crack it.

For example, I have two files, “half1” and “half2”, which are subject to change at any time. I need a permanent file, “whole”, that always contains the concatenation of the current “half1” and “half2” files. And “whole” must appear to be a file (I can't just pipe it in on a command line) for this particular application.

I can obviously do a one-time concatenation (cat half1 half2 > whole) but subsequent changes in “half1” or “half2” won't be reflected in “whole”. Is there some way to make this live/dynamic?

I'm on SunOS 5.10

A named pipe might do:

Code:

mkfifo whole
while true
do
        cat half1 half2 > whole
done

But if that loop ever stops running, the 'file' will block.

Ah, effectively a "replinishing" pipe. That would work. The downside, as you mentioned, is that it must be supported by a running process.

It would be nice to have a native file type (again, like an SQL view) that contains "instructions" to materialize data, but only materializes such data when it is read.

Native files don't do that; they're lists of bytes.

SQL also requires a running process to support it, you might've noticed. These things don't just do themselves.