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SETENV(P) SETENV(P)
NAME
setenv - 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 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 â€â€™=â€â€™ 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 behav-
ior of setenv() is undefined. The setenv() function shall update the list of point-
ers to which environ points.
The strings described by envname and envval are copied by this function.
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 â€â€™=â€â€™ 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 appli-
cations.
RATIONALE
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
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() 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() func-
tion to delete environmental variables, without specifying an additional interface.
The putenv() function 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 ALSO
exec() , 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 .
POSIX 2003 SETENV(P)
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On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
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