Name
putenv — change or add an environment variable
Synopsis
#include <stdlib.h>
int putenv( |
char *string); |
![[Note]](../stylesheet/note.png) |
Note | ||
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DESCRIPTION
The putenv() function adds
or changes the value of environment variables. The argument
string is of the form
name=value. If name does not already exist
in the environment, then string is added to the
environment. If name does exist, then the
value of name in
the environment is changed to value. The string pointed to
by string becomes
part of the environment, so altering the string changes the
environment.
NOTES
The putenv() function is not
required to be reentrant, and the one in libc4, libc5 and
glibc 2.0 is not, but the glibc 2.1 version is.
Description for libc4, libc5, glibc: If the argument
string is of the form
name, and does not
contain an '=' character, then the variable name is removed from the
environment. If putenv() has to
allocate a new array environ,
and the previous array was also allocated by putenv(), then it will be freed. In no case
will the old storage associated to the environment variable
itself be freed.
The libc4 and libc5 and glibc 2.1.2 versions conform to
SUSv2: the pointer string given to putenv() is used. In particular, this
string becomes part of the environment; changing it later
will change the environment. (Thus, it is an error is to call
putenv() with an automatic
variable as the argument, then return from the calling
function while string
is still part of the environment.) However, glibc 2.0-2.1.1
differs: a copy of the string is used. On the one hand this
causes a memory leak, and on the other hand it violates
SUSv2. This has been fixed in glibc 2.1.2.
The 4.4BSD version, like glibc 2.0, uses a copy.
SUSv2 removes the const from
the prototype, and so does glibc 2.1.3.
COLOPHON
This page is part of release 3.24 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
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Copyright 1993 David Metcalfe (davidprism.demon.co.uk) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. References consulted: Linux libc source code Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) 386BSD man pages Single UNIX Specification, Version 2 Modified Thu Apr 8 15:00:12 1993, David Metcalfe Modified Sat Jul 24 18:44:45 1993, Rik Faith (faithcs.unc.edu) Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aebcwi.nl) Modified Mon Oct 11 11:11:11 1999 by Andries Brouwer (aebcwi.nl) Modified Wed Nov 10 00:02:26 1999 by Andries Brouwer (aebcwi.nl) Modified Sun May 20 22:17:20 2001 by Andries Brouwer (aebcwi.nl) |