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 function 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, Copyright (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.opengroup.org/unix/online.html .