getenv—look up environment variable #include <stdlib.h>
char *getenv(const char *name);
Description
getenv searches the list of environment variable names and values
(using the global pointer “char **environ”) for a variable whose
name matches the string at name. If a variable name matches,
getenv returns a pointer to the associated value.
Returns
NULL if there is no such environment variable.
Portability
getenv is ANSI, but the rules for properly forming names of environment
variables vary from one system to another.
getenv requires a global pointer environ.