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 (consult the correspond-
       ing 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 envi-
       ronment 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 vari-
       ables, 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 ulti-
       mate 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 Technol-
       ogy  --	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 Stan-
       dard 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 .

IEEE
/The Open Group						       2013								SETENV(3P)