SETENV(3)                  POSIX Programmer's Manual                 SETENV(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.1-2017, <stdlib.h>, <sys_types.h>,
       <unistd.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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                  2017                            SETENV(3)
