bionic (3) setenv.3posix.gz

Provided by: manpages-posix-dev_2013a-2_all bug

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>


       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 .