setenv(3p) — Linux manual page


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

       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.1‐2017, 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 1003.1-2017, 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)

Pages that refer to this page: stdlib.h(0p)getenv(3p)putenv(3p)unsetenv(3p)