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



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

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 .



IEEE/The Open Group                  2017                            PUTENV(3)
