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



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

NAME
       setenv - add or change environment variable

SYNOPSIS
       #include <stdlib.h>

       int setenv(const char *envname, const char *envval, int overwrite);


DESCRIPTION
       The  setenv()  function  shall  update  or add a variable in the environment of the calling process. The envname argument
       points to a string containing the name of an environment variable to be added or altered. The environment variable  shall
       be  set  to the value to which envval points. The function shall fail if envname points to a string which contains an '='
       character. If the environment variable named by envname already exists and the value of overwrite is non-zero, the  func-
       tion  shall  return  success  and  the environment shall be updated. If the environment variable named by envname already
       exists and the value of overwrite is zero, the function shall return success and the environment shall remain unchanged.

       If the application modifies environ or the pointers to which it points,  the  behavior  of  setenv()  is  undefined.  The
       setenv() function shall update the list of pointers to which environ points.

       The strings described by envname and envval are copied by this function.

       The  setenv()  function  need  not  be  reentrant.  A function that is not required to be reentrant is not required to be
       thread-safe.

RETURN VALUE
       Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, errno set to indicate the error, and
       the environment shall be unchanged.

ERRORS
       The setenv() function shall fail if:

       EINVAL The name argument is a null pointer, points to an empty string, or points to a string containing an '=' character.

       ENOMEM Insufficient memory was available to add a variable or its value to the environment.


       The following sections are informative.

EXAMPLES
       None.

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

RATIONALE
       Unanticipated  results  may  occur if setenv() changes the external variable environ. In particular, if the optional envp
       argument to main() is present, it is not changed, and thus may point to an obsolete copy of the environment (as  may  any
       other  copy  of  environ).  However,  other  than  the aforementioned restriction, the developers of IEEE Std 1003.1-2001
       intended that the traditional method of walking through the environment by way of the environ pointer must be supported.

       It was decided that setenv() should be required by this revision because it addresses a piece of  missing  functionality,
       and does not impose a significant burden on the implementor.

       There  was  considerable  debate  as  to  whether  the  System V putenv() function or the BSD setenv() function should be
       required as a mandatory function.  The setenv() function was chosen  because  it  permitted  the  implementation  of  the
       unsetenv()  function to delete environmental variables, without specifying an additional interface. The putenv() function
       is available as an XSI extension.

       The standard developers considered requiring that setenv() indicate an error when a call to it would result in  exceeding
       {ARG_MAX}.  The requirement was rejected since the condition might be temporary, with the application eventually reducing
       the environment size. The ultimate success or failure depends on the size at the time of a call to exec, which returns an
       indication of this error condition.

FUTURE DIRECTIONS
       None.

SEE ALSO
       exec(), getenv(), unsetenv(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>, <sys/types.h>, <unistd.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    SETENV(3P)