PUTENV(3P)						     POSIX Programmer's Manual							PUTENV(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing 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 appli-
       cation  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.1-2008, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	Portable  Operating  System  Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/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						       2013								PUTENV(3P)