Execute SET command in c program

Question

I created a little mini shell and it let's the user enter a command like 'ls' and it will list the contents of the directory like it's supposed to using execv() in my code, but that doesn't seem to work for when the user enters something like 'set name="bob"'. I've been looking all over the place for what I should use in my code to execute a set command when the user enters it and the best I can find is system(), but that still isn't working for me. Any ideas?

Answer 1

set is a shell-builtin command, not an external command (indeed it needs to be to have the intended effect, which is to modify a shell variable within the shell process itself).

This means that you need to look for and handle set within your shell itself, by adding the named variable to some internal data structure that tracks shell variables (or updating it if it already exists there).

Answer 2

Since you're doing a fork-and-exec or a system(), the command is really being run in a separate process. What happens in that process (like setting an environment variable) does not affect the parent's environment. (A separate issue is that set doesn't actually create an environment variable. You'd need export in [ba]sh or setenv in [t]csh to do that.)

So you need to code your mini-shell to handle the set command explicitly, rather than passing it off to another program.

Answer 3

You might want to look at setenv(3) and getenv(3). These are functions for changing and reading environment variables from within a C program.