#include <stdio.h>
#include <unistd.h>

extern char ** environ;
int main(int argc, char* argv[], char* envp[])
{
    char* v[2]; char* newenv[3];
    if (argc < 2) return -1;

    // Construct the argument array
    v[0] = "/usr/bin/env";   v[1] = NULL;

    // Construct the environment variable array
    newenv[0] = "AAA=aaa"; newenv[1] = "BBB=bbb"; newenv[2] = NULL;

    switch(argv[1][0]) {
    case '1': // Passing no environment variable.
        execve(v[0], v, NULL);
    case '2': // Passing a new set of environment variables.
        execve(v[0], v, newenv);
    case '3': // Passing all the environment variables.
        execve(v[0], v, environ);
    default:
        execve(v[0], v, NULL);
    }
}