mirror of https://github.com/mkerrisk/man-pages
138 lines
3.6 KiB
Groff
138 lines
3.6 KiB
Groff
.\" Copyright 2001 John Levon <moz@compsoc.man.ac.uk>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" Additions, aeb, 2001-10-17.
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.TH CLEARENV 3 2017-09-15 "Linux" "Linux Programmer's Manual"
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.SH NAME
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clearenv \- clear the environment
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.PP
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.B "int clearenv(void);"
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.fi
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.PP
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.PP
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.BR clearenv ():
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/* Glibc since 2.19: */ _DEFAULT_SOURCE
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|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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.SH DESCRIPTION
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The
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.BR clearenv ()
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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
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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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.BR putenv (3)
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and
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.BR setenv (3).
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.SH RETURN VALUE
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The
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.BR clearenv ()
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function returns zero on success, and a nonzero
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value on failure.
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.\" Most versions of UNIX return -1 on error, or do not even have errors.
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.\" Glibc info and the Watcom C library document "a nonzero value".
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.SH VERSIONS
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Available since glibc 2.0.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lb lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR clearenv ()
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T} Thread safety MT-Unsafe const:env
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.TE
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.sp 1
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.SH CONFORMING TO
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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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.BR clearenv ()
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and
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.BR putenv (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 \[sc]B.4.6.1).
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However, POSIX.1-2001
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adds only
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.BR putenv (3),
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and rejected
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.BR clearenv ().
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.SH NOTES
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On systems where
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.BR clearenv ()
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is unavailable, the assignment
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.PP
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.in +4n
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.EX
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environ = NULL;
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.EE
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.in
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.PP
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will probably do.
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.PP
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The
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.BR clearenv ()
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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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.BR exec (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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.PP
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Note that the main effect of
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.BR clearenv ()
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is to adjust the value of the pointer
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.BR environ (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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.PP
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The DG/UX and Tru64 man pages write: If
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.I environ
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has been modified by anything other than the
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.BR putenv (3),
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.BR getenv (3),
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or
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.BR clearenv ()
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functions, then
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.BR clearenv ()
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will return an error and the process environment will remain unchanged.
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.\" .LP
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.\" HP-UX has a ENOMEM error return.
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.SH SEE ALSO
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.BR getenv (3),
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.BR putenv (3),
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.BR setenv (3),
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.BR unsetenv (3),
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.BR environ (7)
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