'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright (C) 2004, 2007 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" 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@gmail.com>
.\"     Changed unsetenv() prototype; added EINVAL error
.\"     Noted nonstandard behavior of setenv() if name contains '='
.\" 2005-08-12, mtk, glibc 2.3.4 fixed the "name contains '='" bug
.\"
.TH setenv 3 2023-02-05 "Linux man-pages 6.03"
.SH NAME
setenv \- change or add an environment variable
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "int setenv(const char *" name ", const char *" value ", int " overwrite );
.BI "int unsetenv(const char *" name );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR setenv (),
.BR unsetenv ():
.nf
    _POSIX_C_SOURCE >= 200112L
        || /* glibc <= 2.19: */ _BSD_SOURCE
.fi
.SH DESCRIPTION
The
.BR setenv ()
function adds the variable
.I name
to the
environment with the value
.IR value ,
if
.I name
does not
already exist.
If
.I name
does exist in the environment, then
its value is changed to
.I value
if
.I overwrite
is nonzero;
if
.I overwrite
is zero, then the value of
.I name
is not changed (and
.BR setenv ()
returns a success status).
This function makes copies of the strings pointed to by
.I name
and
.I value
(by contrast with
.BR putenv (3)).
.PP
The
.BR unsetenv ()
function deletes the variable
.I name
from
the environment.
If
.I name
does not exist in the environment,
then the function succeeds, and the environment is unchanged.
.SH RETURN VALUE
.BR setenv ()
and
.BR unsetenv ()
functions return zero on success,
or \-1 on error, with
.I errno
set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
.I name
is NULL, points to a string of length 0,
or contains an \[aq]=\[aq] character.
.TP
.B ENOMEM
Insufficient memory to add a new variable to the environment.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR setenv (),
.BR unsetenv ()
T}	Thread safety	MT-Unsafe const:env
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
.SH NOTES
POSIX.1 does not require
.BR setenv ()
or
.BR unsetenv ()
to be reentrant.
.PP
Prior to glibc 2.2.2,
.BR unsetenv ()
was prototyped
as returning
.IR void ;
more recent glibc versions follow the
POSIX.1-compliant prototype shown in the SYNOPSIS.
.SH BUGS
POSIX.1 specifies that if
.I name
contains an \[aq]=\[aq] character, then
.BR setenv ()
should fail with the error
.BR EINVAL ;
however, versions of glibc before glibc 2.3.4 allowed an \[aq]=\[aq] sign in
.IR name .
.SH SEE ALSO
.BR clearenv (3),
.BR getenv (3),
.BR putenv (3),
.BR environ (7)