putenv - change or add value to environment
#include <stdlib.h>
int putenv(char *string);
The putenv() function makes the value of the environment variable
name equal to value by altering an existing variable or creating
a new one. In either case, the string pointed to by string becomes part
of the environment, so altering the string will change the environment.
The string argument points to a string of the form
name=value. The space used by string is no
longer used once a new string-defining name is passed to
putenv(). If there is no equals sign (=) present as a
separator, then string is treated as the name of an
environment variable to remove from the environment, as though
unsetenv(3C) had been called.
The putenv() function uses malloc(3C) to enlarge the
environment.
After putenv() is called, environment variables are not in
alphabetical order.
Upon successful completion, putenv() returns 0. Otherwise, it returns a
non-zero value and sets errno to indicate the error.
The putenv() function may fail if:
ENOMEM
Insufficient memory was available.
The putenv() function can be safely called from multithreaded programs.
Caution must be exercised when using this function and getenv(3C) in
multithreaded programs. These functions examine and modify the environment
list, which is shared by all threads in a program. The system prevents the
list from being accessed simultaneously by two different threads. It does not,
however, prevent two threads from successively accessing the environment list
using putenv() or getenv().
See attributes(7) for descriptions of the following attributes:
| ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
| Interface Stability |
Standard |
| MT-Level |
Safe |
The string argument should not be an automatic variable. It should be
declared static if it is declared within a function because it cannot be
automatically declared. A potential error is to call putenv() with a
pointer to an automatic variable as the argument and to then exit the calling
function while string is still part of the environment.