SETENV(P) POSIX Programmer's Manual SETENV(P)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.
If the application modifies environ or the pointers to which it points,
the behavior of setenv() is undefined. The setenv() function shall
update the list of pointers to which environ points.
The strings described by envname and envval are copied by this func‐
tion.
The setenv() function need not be reentrant. A function that is not
required to be reentrant is not required to 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 name argument is a null pointer, 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 developers of IEEE Std 1003.1-2001
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 revision
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 an XSI extension.
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.
FUTURE DIRECTIONS
None.
SEE ALSOexec() , getenv() , unsetenv() , the Base Definitions volume of
IEEE Std 1003.1-2001, <stdlib.h>, <sys/types.h>, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SETENV(P)
