SETENV(3P) POSIX Programmer's Manual SETENV(3P)PROLOG
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.
NAMEsetenv — 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 con‐
taining 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 envi‐
ron points.
The strings described by envname and envval are copied by this func‐
tion.
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 vari‐
able 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() func‐
tion 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 vari‐
ables, without specifying an additional interface. The putenv() func‐
tion 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.1‐2008, <stdlib.h>, <sys_types.h>,
<unistd.h>
COPYRIGHT
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 Electri‐
cal 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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SETENV(3P)
