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### 2.18 `getenv`—look up environment variable

Synopsis

         #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
A pointer to the (string) value of the environment variable, or `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`.