PROLOG

       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.

NAME

       putenv — change or add a value to an environment

SYNOPSIS

       #include <stdlib.h>

       int putenv(char *string);

DESCRIPTION

       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.

RETURN VALUE

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

ERRORS

       The putenv() function may fail if:

       ENOMEM Insufficient memory was available.

       The following sections are informative.

EXAMPLES

   Changing the Value of an Environment Variable
       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);

APPLICATION USAGE

       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().

RATIONALE

       Refer to the RATIONALE section in setenv().

FUTURE DIRECTIONS

       None.

SEE ALSO

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

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

COPYRIGHT

       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 .