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       putenv - change or add an environment variable


       #include <stdlib.h>

       int putenv(char *string);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       putenv(): _XOPEN_SOURCE
           || /* Glibc since 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _SVID_SOURCE


       The  putenv()  function  adds or changes the value of environment variables.  The argument
       string is of the form name=value.  If name does not already exist in the environment, then
       string  is  added  to  the environment.  If name does exist, then the value of name in the
       environment is changed to value.  The string pointed to by  string  becomes  part  of  the
       environment, so altering the string changes the environment.


       The  putenv()  function  returns  zero  on success, or nonzero if an error occurs.  In the
       event of an error, errno is set to indicate the cause.


       ENOMEM Insufficient space to allocate new environment.


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue               │
       │putenv()  │ Thread safety │ MT-Unsafe const:env │


       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.


       The putenv() function is not required to be reentrant, and the one in glibc  2.0  is  not,
       but the glibc 2.1 version is.

       Since  version 2.1.2, the glibc implementation conforms to SUSv2: the pointer string given
       to putenv() is used.  In particular, this string becomes part of the environment; changing
       it  later  will  change  the  environment.  (Thus, it is an error to call putenv() with an
       automatic variable as the argument, then return from the calling function while string  is
       still  part  of  the environment.)  However, glibc versions 2.0 to 2.1.1 differ: a copy of
       the string is used.  On the one hand this causes a memory leak, and on the other  hand  it
       violates SUSv2.

       The 4.4BSD version, like glibc 2.0, uses a copy.

       SUSv2 removes the const from the prototype, and so does glibc 2.1.3.

       The  GNU  C  library  implementation provides a nonstandard extension.  If string does not
       include an equal sign:


       then the named variable is removed from the caller's environment.


       clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)


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