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

       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.

       setenv — add or change environment variable

       #include <stdlib.h>

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

       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

       The setenv() function shall update the list of pointers to which environ

       The strings described by envname and envval are copied by this function.

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

       Upon successful completion, zero shall be returned. Otherwise, -1 shall
       be returned, errno set to indicate the error, and the environment shall
       be unchanged.

       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.


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

       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().


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

       The Base Definitions volume of POSIX.1‐2017, <stdlib.h>, <sys_types.h>,

       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 .

       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                   2017                            SETENV(3P)