597b026757
The clearenv(3) function allows us to clear all environment variable in one shot. This may be useful for security programs that want to control the environment or what variables are passed to new spawned programs. Reviewed by: scf, markj (secteam), 0mp (manpages) Differential Revision: https://reviews.freebsd.org/D28223
247 lines
5.5 KiB
Groff
247 lines
5.5 KiB
Groff
.\" Copyright (c) 1988, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getenv.3 8.2 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd November 7, 2021
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.Dt GETENV 3
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.Os
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.Sh NAME
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.Nm clearenv ,
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.Nm getenv ,
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.Nm putenv ,
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.Nm setenv ,
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.Nm unsetenv
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.Nd environment variable functions
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft int
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.Fn clearenv "void"
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.Ft char *
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.Fn getenv "const char *name"
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.Ft int
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.Fn setenv "const char *name" "const char *value" "int overwrite"
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.Ft int
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.Fn putenv "char *string"
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.Ft int
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.Fn unsetenv "const char *name"
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.Sh DESCRIPTION
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These functions set, unset and fetch environment variables from the
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host
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.Em environment list .
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.Pp
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The
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.Fn clearenv
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function clears all environment variables.
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New variables can be added using
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.Fn setenv
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and
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.Fn putenv .
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.Pp
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The
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.Fn getenv
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function obtains the current value of the environment variable,
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.Fa name .
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The application should not modify the string pointed
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to by the
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.Fn getenv
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function.
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.Pp
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The
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.Fn setenv
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function inserts or resets the environment variable
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.Fa name
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in the current environment list.
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If the variable
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.Fa name
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does not exist in the list,
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it is inserted with the given
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.Fa value .
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If the variable does exist, the argument
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.Fa overwrite
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is tested; if
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.Fa overwrite
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is zero, the
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variable is not reset, otherwise it is reset
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to the given
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.Fa value .
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.Pp
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The
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.Fn putenv
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function takes an argument of the form ``name=value'' and
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puts it directly into the current environment,
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so altering the argument shall change the environment.
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If the variable
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.Fa name
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does not exist in the list,
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it is inserted with the given
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.Fa value .
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If the variable
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.Fa name
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does exist, it is reset to the given
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.Fa value .
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.Pp
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The
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.Fn unsetenv
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function
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deletes all instances of the variable name pointed to by
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.Fa name
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from the list.
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.Pp
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If corruption (e.g., a name without a value) is detected while making a copy of
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environ for internal usage, then
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.Fn setenv ,
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.Fn unsetenv
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and
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.Fn putenv
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will output a warning to stderr about the issue, drop the corrupt entry and
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complete the task without error.
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.Sh RETURN VALUES
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The
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.Fn getenv
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function returns the value of the environment variable as a
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.Dv NUL Ns
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-terminated string.
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If the variable
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.Fa name
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is not in the current environment,
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.Dv NULL
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is returned.
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.Pp
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.Rv -std clearenv setenv putenv unsetenv
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The function
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.Fn getenv ,
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.Fn setenv
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or
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.Fn unsetenv
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failed because the
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.Fa name
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is a
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.Dv NULL
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pointer, points to an empty string, or points to a string containing an
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.Dq Li \&=
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character.
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.Pp
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The function
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.Fn putenv
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failed because
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.Fa string
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is a
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.Dv NULL
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pointer,
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.Fa string
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is without an
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.Dq Li \&=
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character or
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.Dq Li \&=
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is the first character in
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.Fa string .
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This does not follow the
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.Tn POSIX
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specification.
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.It Bq Er ENOMEM
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The function
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.Fn setenv ,
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.Fn unsetenv
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or
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.Fn putenv
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failed because they were unable to allocate memory for the environment.
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.El
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.Sh SEE ALSO
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.Xr csh 1 ,
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.Xr sh 1 ,
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.Xr execve 2 ,
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.Xr environ 7
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.Sh STANDARDS
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The
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.Fn getenv
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function conforms to
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.St -isoC .
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The
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.Fn setenv ,
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.Fn putenv
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and
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.Fn unsetenv
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functions conforms to
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.St -p1003.1-2001 .
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.Sh HISTORY
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The functions
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.Fn setenv
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and
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.Fn unsetenv
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appeared in
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.At v7 .
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The
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.Fn putenv
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function appeared in
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.Bx 4.3 Reno .
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.Pp
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Until
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.Fx 7.0 ,
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.Fn putenv
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would make a copy of
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.Fa string
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and insert it into the environment using
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.Fn setenv .
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This was changed to use
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.Fa string
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as the memory location of the ``name=value'' pair to follow the
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.Tn POSIX
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specification.
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.Pp
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The
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.Fn clearenv
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was added in
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.Fx 14 .
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.Sh BUGS
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Successive calls to
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.Fn setenv
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that assign a larger-sized
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.Fa value
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than any previous value to the same
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.Fa name
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will result in a memory leak.
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The
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.Fx
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semantics for this function
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(namely, that the contents of
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.Fa value
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are copied and that old values remain accessible indefinitely) make this
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bug unavoidable.
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Future versions may eliminate one or both of these
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semantic guarantees in order to fix the bug.
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