Name

putenv — change or add an environment variable

Synopsis

        #include <stdlib.h>
int putenv( char *string);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
putenv():
_XOPEN_SOURCE || /* Glibc since 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
*/ _SVID_SOURCE

DESCRIPTION

The putenv() function adds or changes the value of environment variables. The argument string is of the form name=value. If name does not already exist in the environment, then string is added to the environment. If name does exist, then the value of name in the environment is changed to value. The string pointed to by string becomes part of the environment, so altering the string changes the environment.

RETURN VALUE

The putenv() function returns zero on success, or nonzero if an error occurs. In the event of an error, errno is set to indicate the cause.

ERRORS

ENOMEM

Insufficient space to allocate new environment.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
putenv() Thread safety MT-Unsafe const:env

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES

The putenv() function is not required to be reentrant, and the one in glibc 2.0 is not, but the glibc 2.1 version is.

Since version 2.1.2, the glibc implementation conforms to SUSv2: the pointer string given to putenv() is used. In particular, this string becomes part of the environment; changing it later will change the environment. (Thus, it is an error is to call putenv() with an automatic variable as the argument, then return from the calling function while string is still part of the environment.) However, glibc versions 2.0 to 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.

The 4.4BSD version, like glibc 2.0, uses a copy.

SUSv2 removes the const from the prototype, and so does glibc 2.1.3.

SEE ALSO

clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)

COLOPHON

This page is part of release 4.16 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)

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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 (faithcs.unc.edu)
Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aebcwi.nl)
Modified Mon Oct 11 11:11:11 1999 by Andries Brouwer (aebcwi.nl)
Modified Wed Nov 10 00:02:26 1999 by Andries Brouwer (aebcwi.nl)
Modified Sun May 20 22:17:20 2001 by Andries Brouwer (aebcwi.nl)