.\" Copyright 2001 John Levon <moz@compsoc.man.ac.uk>
.\"
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.\" Additions, aeb, 2001-10-17.
.TH CLEARENV 3  2007-07-26 "Linux" "Linux Programmer's Manual"
.SH NAME
clearenv \- clear the environment
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "int clearenv(void);"
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR clearenv ():
_SVID_SOURCE || _XOPEN_SOURCE
.SH DESCRIPTION
The
.BR clearenv ()
function clears the environment of all name-value
pairs and sets the value of the external variable
.I environ
to NULL.
.SH "RETURN VALUE"
The
.BR clearenv ()
function returns zero on success, and a non-zero
value on failure.
.\" Most versions of Unix return -1 on error, or do not even have errors.
.\" Glibc info and the Watcom C library document "a non-zero value".
.SH VERSIONS
Not in libc4, libc5.
In glibc since glibc 2.0.
.SH "CONFORMING TO"
Various Unix variants (DG/UX, HP-UX, QNX, ...).
POSIX.9 (bindings for FORTRAN77).
POSIX.1-1996 did not accept
.BR clearenv ()
and
.BR putenv (3),
but changed its mind and scheduled these functions for some
later issue of this standard (cf. B.4.6.1).
However, POSIX.1-2001
only adds
.BR putenv (3),
and rejected
.BR clearenv ().
.SH NOTES
Used in security-conscious applications.
If it is unavailable
the assignment
.RS
.nf
    environ = NULL;
.fi
.RE
will probably do.
.LP
The DG/UX and Tru64 man pages write: If
.I environ
has been modified by anything other than the
.BR putenv (3),
.BR getenv (3),
or
.BR clearenv ()
functions, then
.BR clearenv ()
will return an error and the process environment will remain unchanged.
.\" .LP
.\" HP-UX has a ENOMEM error return.
.SH "SEE ALSO"
.BR getenv (3),
.BR putenv (3),
.BR setenv (3),
.BR unsetenv (3),
.BR environ (7)