function searches the environment list to find the
and returns a pointer to the corresponding
function returns a pointer to the value in the
environment, or NULL if there is no match.
SVr4, POSIX.1-2001, 4.3BSD, C89, C99.
The strings in the environment list are of the form name=value.
As typically implemented,
returns a pointer to a string within the environment list.
The caller must take care not to modify this string,
since that would change the environment of the process.
The implementation of
is not required to be reentrant.
The string pointed to by the return value of
may be statically allocated,
and can be modified by a subsequent call to