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] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
setenv(), unsetenv():
_POSIX_C_SOURCE >= 200112L || /* Glibc versions <= 2.19:
*/ _BSD_SOURCE

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

name is 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

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, 4.3BSD.

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.

SEE ALSO

clearenv(3), getenv(3), putenv(3), environ(7)

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