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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(): _SVID_SOURCE || _XOPEN_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


       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

       │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  is  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.


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


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