Name
setenv — change or add an environment variable
Synopsis
#include <stdlib.h>
int
setenv( |
const char *name, |
| const char *value, | |
int overwrite); |
int
unsetenv( |
const char *name); |
![[Note]](../stylesheet/note.png) |
Note | |||
|---|---|---|---|---|
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DESCRIPTION
The setenv() function adds
the variable name to
the environment with the value value, if name does not already exist. If
name does exist in
the environment, then its value is changed to value if overwrite is nonzero; if
overwrite is zero,
then the value of name is not changed (and
setenv() returns a success
status). This function makes copies of the strings pointed to
by name and
value (by contrast
with putenv(3)).
The unsetenv() function
deletes the variable name from the environment. If
name does not exist
in the environment, then the function succeeds, and the
environment is unchanged.
RETURN VALUE
The setenv() function
returns zero on success, or −1 on error, with
errno set to indicate the cause
of the error.
The unsetenv() function
returns zero on success, or −1 on error, with
errno set to indicate the cause
of the error.
ERRORS
- EINVAL
-
nameis NULL, points to a string of length 0, or contains an '=' character. - ENOMEM
-
Insufficient memory to add a new variable to the environment.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
setenv(), unsetenv() |
Thread safety | MT-Unsafe const:env |
NOTES
POSIX.1 does not require setenv() or unsetenv() to be reentrant.
Prior to glibc 2.2.2, unsetenv() was prototyped as returning
void; more recent glibc versions
follow the POSIX.1-compliant prototype shown in the
SYNOPSIS.
BUGS
POSIX.1 specifies that if name contains an '=' character,
then setenv() should fail with
the error EINVAL; however,
versions of glibc before 2.3.4 allowed an '=' sign in
name.
COLOPHON
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright 1993 David Metcalfe (davidprism.demon.co.uk) and Copyright (C) 2004, 2007 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) 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. %%%LICENSE_END 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 (faithcs.unc.edu) Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aebcwi.nl) Modified 9 Jun 2004, Michael Kerrisk <mtk.manpagesgmail.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 |