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

PROLOG         top

       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         top

       setenv — add or change environment variable

SYNOPSIS         top

       #include <stdlib.h>

       int setenv(const char *envname, const char *envval, int overwrite);

DESCRIPTION         top

       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

       The setenv() function need not be thread-safe.

RETURN VALUE         top

       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         top

       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         top



       See exec() for restrictions on changing the environment in multi-
       threaded applications.

RATIONALE         top

       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(3p).



SEE ALSO         top

       exec(1p), getenv(3p), putenv(3p), unsetenv(3p)

       The Base Definitions volume of POSIX.1‐2008, stdlib.h(0p),
       sys_types.h(0p), unistd.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                          SETENV(3P)