207 lines
4.8 KiB
HTML
207 lines
4.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of CLEARENV</TITLE>
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</HEAD><BODY>
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<H1>CLEARENV</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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clearenv - clear the environment
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/stdlib.h">stdlib.h</A>></B>
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<B>int clearenv(void);</B>
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</PRE>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>clearenv</B>():
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<BR> /* Glibc since 2.19: */ _DEFAULT_SOURCE
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<BR> || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>clearenv</B>()
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function clears the environment of all name-value
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pairs and sets the value of the external variable
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<I>environ</I>
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to NULL.
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After this call, new variables can be added to the environment using
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<B><A HREF="/cgi-bin/man/man2html?3+putenv">putenv</A></B>(3)
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and
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<B><A HREF="/cgi-bin/man/man2html?3+setenv">setenv</A></B>(3).
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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The
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<B>clearenv</B>()
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function returns zero on success, and a nonzero
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value on failure.
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<A NAME="lbAF"> </A>
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<H2>VERSIONS</H2>
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Available since glibc 2.0.
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<A NAME="lbAG"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>clearenv</B>()
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</TD><TD>Thread safety</TD><TD>MT-Unsafe const:env<BR></TD></TR>
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</TABLE>
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<P>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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Various UNIX variants (DG/UX, HP-UX, QNX, ...).
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POSIX.9 (bindings for FORTRAN77).
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POSIX.1-1996 did not accept
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<B>clearenv</B>()
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and
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<B><A HREF="/cgi-bin/man/man2html?3+putenv">putenv</A></B>(3),
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but changed its mind and scheduled these functions for some
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later issue of this standard (see §B.4.6.1).
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However, POSIX.1-2001
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adds only
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<B><A HREF="/cgi-bin/man/man2html?3+putenv">putenv</A></B>(3),
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and rejected
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<B>clearenv</B>().
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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On systems where
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<B>clearenv</B>()
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is unavailable, the assignment
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<P>
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environ = NULL;
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<P>
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will probably do.
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<P>
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The
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<B>clearenv</B>()
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function may be useful in security-conscious applications that want to
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precisely control the environment that is passed to programs
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executed using
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<B><A HREF="/cgi-bin/man/man2html?3+exec">exec</A></B>(3).
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The application would do this by first clearing the environment
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and then adding select environment variables.
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<P>
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Note that the main effect of
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<B>clearenv</B>()
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is to adjust the value of the pointer
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<B><A HREF="/cgi-bin/man/man2html?7+environ">environ</A></B>(7);
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this function does not erase the contents of the buffers
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containing the environment definitions.
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<P>
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The DG/UX and Tru64 man pages write: If
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<I>environ</I>
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has been modified by anything other than the
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<B><A HREF="/cgi-bin/man/man2html?3+putenv">putenv</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+getenv">getenv</A></B>(3),
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or
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<B>clearenv</B>()
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functions, then
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<B>clearenv</B>()
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will return an error and the process environment will remain unchanged.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+getenv">getenv</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+putenv">putenv</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+setenv">setenv</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+unsetenv">unsetenv</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+environ">environ</A></B>(7)
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<A NAME="lbAK"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="5"><A HREF="#lbAF">VERSIONS</A><DD>
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<DT id="6"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="7"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="8"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="9"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="10"><A HREF="#lbAK">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:37 GMT, March 31, 2021
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