how to map a file to a shell command to be executed when you `cat` that file? [closed]

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I'd like to create a file and hook it up somehow to a shell command that gets executed whenever I cat that file. So that the content of the file is the stdout of the shell command.

Something like /proc/meminfo.

Thanks

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/proc/meminfo lives in a special filesystem, procfs, that is implemented by the kernel. You could use FUSE to do something similar in userspace.

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We used to do this "back in the day" to make program generated .finger files.

Make your file into a named pipe. You use the mknod program to do this.

Then make a program, which can be a shell script, that continuously loops and writes content into that named pipe.

#!/bin/sh

mknod file p 2>/dev/null
while true; do
        (
                echo This is my file.
                echo There are many like it.
                echo But this one is mine.
        ) >> file
done

For some reason it won't let me kill that with Control-C, so I have to use Control-Z, then kill %1.

Now when you cat file you will get the contents, like this:

$ cat file 
This is my file.
There are many like it.
But this one is mine.

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Perhaps you should turn the problem around and write a shell command and execute that instead of cat to start with? Anything "echo"'ed will appear on stdout. The solution you are proposing is "not the unix way".