What does execve() do?

Question

What exactly does execve() do? I've tried looking at the documentation (http://linux.die.net/man/2/execve) but given that I'm very new to linux and this sort of programming it doesn't make a lot of sense. What I want to do is be able to execute this command:

nc -l -p someport -e /bin/sh

Can I do something like the following (where someport is a number such as 4444)

char *command[2];
command[0] = "nc -l -p someport -e /bin/sh"
execve(command[0], name, NULL);

Answer 1

Correct usage is

extern char * const environ[];
char * const command[] = {"nc", "-l", "-p", "porthere", "-e", "/bin/sh", NULL};
execve("/usr/bin/nc", command, environ);

You must use a full pathname, not a short name such as "nc" (more precisely: no PATH search is done, the pathname must be an actual existing file), and you must split arguments into separate strings beforehand. You also need to propagate the environment somehow, either via the extern environ mentioned in the above snippet or as obtained from the third parameter of main(); the latter is slightly more standards-blessed but may be more painful to pass around as needed.

Answer 2

execve replaces the current process with a new process, running the command you specified as its first argument.

Chances are pretty decent that you want execvp or execlp instead -- you haven't mentioned anything about wanting to provide the environment for the child, but from the looks of things you probably do want the path searched to find the executable you're using.