.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" 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.\" manual page may be incorrect or out-of-date.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
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 18:20:58 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
.\" Modified 9 Jun 2004, Michael Kerrisk <mtk-manpages@gmx.net>
.\"     Changed unsetenv() prototype; added EINVAL error
.\"     Noted non-standard behaviour of setenv() if name contains '='
.\" 2005-08-12, mtk, glibc 2.3.4 fixed the "name contains '='" bug
.\"
.TH SETENV 3  2004-05-09 "GNU" "Linux Programmer's Manual"
.SH NAME
setenv \- change or add an environment variable
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "int setenv(const char *" name ", const char *" value ", int " overwrite );
.sp
.BI "int unsetenv(const char *" name );
.fi
.SH DESCRIPTION
The
.BR setenv ()
function adds the variable \fIname\fP to the
environment with the value \fIvalue\fP, if \fIname\fP does not
already exist.
If \fIname\fP does exist in the environment, then
its value is changed to \fIvalue\fP if \fIoverwrite\fP is non-zero;
if \fIoverwrite\fP is zero, then the value of \fIname\fP is not
changed.
.PP
The
.BR unsetenv ()
function deletes the variable \fIname\fP from
the environment.
.SH "RETURN VALUE"
The
.BR setenv ()
function returns zero on success, or \-1 if there
was insufficient space in the environment.
The
.BR unsetenv ()
function returns zero on success,
or \-1 on error, with
.I errno
set to indicate the cause of the error.
.SH "ERRORS"
.TP
.B EINVAL
.I name
contained an '=' character.
.SH "CONFORMING TO"
4.3BSD, POSIX.1-2001.
.SH "NOTES"
Prior to glibc 2.2.2,
.BR unsetenv ()
was prototyped
as returning \fIvoid\fP; more recent glibc versions follow the
POSIX.1-2001-compliant prototype shown in the SYNOPSIS.
.SH BUGS
POSIX.1-2001 specifies that if
.I name
contains an '=' character, then
.BR setenv ()
should fail with the error
.BR EINVAL ;
however, versions of glibc before 2.3.4 allowed an '=' sign in
.IR name .
.SH "SEE ALSO"
.BR clearenv (3),
.BR getenv (3),
.BR putenv (3),
.BR environ (7)