This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       The putenv() function manipulates the environment pointed to by environ, and can be used  in  conjunction
       with getenv().

       See exec() for restrictions on changing the environment in multi-threaded applications.

       This routine may use malloc() to enlarge the environment.

       A  potential  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.

       Although the space used by string is no longer used once a new string which defines  name  is  passed  to
       putenv(),  if  any thread in the application has used getenv() to retrieve a pointer to this variable, it
       should not be freed by calling free().  If the changed environment variable is one known  by  the  system
       (such  as  the locale environment variables) the application should never free the buffer used by earlier
       calls to putenv() for the same variable.

       The setenv() function is preferred over this function. One  reason  is  that  putenv()  is  optional  and
       therefore  less portable. Another is that using putenv() can slow down environment searches, as explained
       in the RATIONALE section for getenv().

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                        PUTENV(3POSIX)

       The  putenv()  function  shall  use  the  string  argument to set environment variable values. The string
       argument should point to a string of the form "name=value".  The putenv() function shall make  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 shall become part of the  environment,  so  altering  the
       string shall change the environment.

       The putenv() function need not be thread-safe.

       The putenv() function may fail if:

       ENOMEM Insufficient memory was available.

       Thefollowingsectionsareinformative.

ChangingtheValueofanEnvironmentVariable
       The following example changes the value of the HOME environment variable to the value /usr/home.

           #include <stdlib.h>
           ...
           static char *var = "HOME=/usr/home";
           int ret;

           ret = putenv(var);

       None.

       putenv — change or add a value to an environment

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       Refer to the RATIONALE section in setenv().

       Upon  successful completion, putenv() shall return 0; otherwise, it shall return a non-zero value and set
       errno to indicate the error.

exec, free(), getenv(), malloc(), setenv()

       The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

       #include <stdlib.h>

       int putenv(char *string);