219 lines
5.2 KiB
HTML
219 lines
5.2 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 GETENV</TITLE>
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</HEAD><BODY>
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<H1>GETENV</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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getenv, secure_getenv - get an environment variable
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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>char *getenv(const char *</B><I>name</I><B>);</B>
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<B>char *secure_getenv(const char *</B><I>name</I><B>);</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>secure_getenv</B>():
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_GNU_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>getenv</B>()
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function searches the environment list to find the
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environment variable
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<I>name</I>,
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and returns a pointer to the corresponding
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<I>value</I>
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string.
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<P>
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The GNU-specific
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<B>secure_getenv</B>()
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function is just like
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<B>getenv</B>()
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except that it returns NULL in cases where "secure execution" is required.
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Secure execution is required if one of the following conditions
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was true when the program run by the calling process was loaded:
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<DL COMPACT>
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<DT id="1">*<DD>
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the process's effective user ID did not match its real user ID or
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the process's effective group ID did not match its real group ID
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(typically this is the result of executing a set-user-ID or
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set-group-ID program);
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<DT id="2">*<DD>
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the effective capability bit was set on the executable file; or
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<DT id="3">*<DD>
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the process has a nonempty permitted capability set.
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</DL>
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<P>
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Secure execution may also be required if triggered
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by some Linux security modules.
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<P>
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The
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<B>secure_getenv</B>()
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function is intended for use in general-purpose libraries
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to avoid vulnerabilities that could occur if
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set-user-ID or set-group-ID programs accidentally
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trusted the environment.
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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>getenv</B>()
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function returns a pointer to the value in the
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environment, or NULL if there is no match.
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<A NAME="lbAF"> </A>
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<H2>VERSIONS</H2>
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<B>secure_getenv</B>()
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first appeared in glibc 2.17.
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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>getenv</B>(),
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<B>secure_getenv</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe env<BR></TD></TR>
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</TABLE>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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<B>getenv</B>():
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POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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<P>
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<B>secure_getenv</B>()
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is a GNU extension.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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The strings in the environment list are of the form <I>name=value</I>.
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<P>
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As typically implemented,
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<B>getenv</B>()
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returns a pointer to a string within the environment list.
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The caller must take care not to modify this string,
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since that would change the environment of the process.
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<P>
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The implementation of
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<B>getenv</B>()
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is not required to be reentrant.
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The string pointed to by the return value of
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<B>getenv</B>()
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may be statically allocated,
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and can be modified by a subsequent call to
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<B>getenv</B>(),
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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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or
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<B><A HREF="/cgi-bin/man/man2html?3+unsetenv">unsetenv</A></B>(3).
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<P>
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The "secure execution" mode of
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<B>secure_getenv</B>()
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is controlled by the
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<B>AT_SECURE</B>
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flag contained in the auxiliary vector passed from the kernel to user space.
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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+clearenv">clearenv</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+getauxval">getauxval</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+capabilities">capabilities</A></B>(7),
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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="4"><A HREF="#lbAB">NAME</A><DD>
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<DT id="5"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="6"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="7"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="8"><A HREF="#lbAF">VERSIONS</A><DD>
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<DT id="9"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="10"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="11"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="12"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="13"><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: 00:05:44 GMT, March 31, 2021
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</BODY>
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</HTML>
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