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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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 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.
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.
None.
See exec() for restrictions on changing the environment in multi-
threaded applications.
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).
None.
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)
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 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)
Pages that refer to this page: stdlib.h(0p), getenv(3p), putenv(3p), unsetenv(3p)