apue_getenv.h

#include <stdlib.h>

char *getenv(const char *name);
/* Returns: pointer to value associated with name, NULL if not found */

int putenv(char *str);
/* Returns: 0 if OK, nonzero on error */

int setenv(const char *name, const char *value, int rewrite);
int unsetenv(const char *name);

/* Both return: 0 if OK, −1 on error */