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Linux 2.6 - man page for setenv (linux section 3posix)

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

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 reen-
       trant 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  environ-
	      ment.

       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 par-
       ticular, 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). How-
       ever, 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 env-
       iron 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 implemen-
       tor.

       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  envi-
       ronmental  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 condi-
       tion 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					SETENV(P)


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