PUTENV(3C) Standard C Library Functions PUTENV(3C)

NAME

putenv - change or add value to environment

SYNOPSIS

#include <stdlib.h>

int putenv(char *string);

DESCRIPTION

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.

RETURN VALUES

Upon successful completion, putenv() returns 0. Otherwise, it returns a
non-zero value and sets errno to indicate the error.

ERRORS

The putenv() function may fail if:

ENOMEM
Insufficient memory was available.

USAGE

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().

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | Safe |
+--------------------+-----------------+

SEE ALSO

exec(2), getenv(3C), malloc(3C), attributes(7), environ(7), standards(7)

WARNINGS

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.

June 22, 2016 PUTENV(3C)