PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult 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 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.

       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 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 envname argument 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 standard developers 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 version 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 part of the XSI option.

       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.

       See also the RATIONALE section in getenv().

FUTURE DIRECTIONS

       None.

SEE ALSO

       exec, getenv(), putenv(), unsetenv()

       The Base Definitions volume of POSIX.1‐2008, <stdlib.h>, <sys_types.h>, <unistd.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  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 Standard 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 .