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.\" Copyright 1993 David Metcalfe (david@prism.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.\" manual page may be incorrect or out-of-date.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 (faith@cs.unc.edu)
.\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
.\" Modified Mon Oct 11 11:11:11 1999 by Andries Brouwer (aeb@cwi.nl)
.\" Modified Wed Nov 10 00:02:26 1999 by Andries Brouwer (aeb@cwi.nl)
.TH PUTENV 3 "April 8, 1993" "GNU" "Linux Programmer's Manual"
.SH NAME
putenv \- change or add an environment variable
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "int putenv(const char *" string );
.fi
.SH DESCRIPTION
The \fBputenv()\fP function adds or changes the value of environment
variables. The argument \fIstring\fP is of the form \fIname\fP=\fIvalue\fP.
If \fIname\fP does not already exist in the environment, then
\fIstring\fP is added to the environment. If \fIname\fP does exist,
then the value of \fIname\fP in the environment is changed to
\fIvalue\fP.
The string pointed to by \fIstring\fP becomes part of the environment,
so altering the string changes the environment.
.SH "RETURN VALUE"
The \fBputenv()\fP function returns zero on success, or \-1 if an error
occurs.
.SH ERRORS
.TP
.B ENOMEM
Insufficient space to allocate new environment.
.SH NOTES
The \fBputenv()\fP function is not required to be reentrant, and the
one in libc4, libc5 and glibc2.0 is not, but the glibc2.1 version is.
.LP
Description for libc4, libc5, glibc:
If the argument \fIstring\fP is of the form \fIname\fP,
and does not contain an `=' character, then the variable \fIname\fP
is removed from the environment.
If \fBputenv()\fP has to allocate a new array \fIenviron\fP,
and the previous array was also allocated by \fBputenv()\fP,
then it will be freed. In no case will the old storage associated
to the environment variable itself be freed.
.LP
The libc4 and libc5 versions conform to SUSv2: the pointer \fIstring\fP
given to \fBputenv()\fP is used. In particular, this string becomes
part of the environment; changing it later will change the environment.
However, glibc 2.0-2.1.1 differ: 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 glibc2.1.2.
.LP
The BSD4.4 version, like glibc 2.0, uses a copy.
.LP
SUSv2 removes the `const' from the prototype, and so does glibc 2.2.
.SH "CONFORMING TO"
SVID 3, POSIX, BSD 4.3
.SH "SEE ALSO"
.BR getenv (3),
.BR setenv (3),
.BR unsetenv (3),
.BR environ (7)
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