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():
_SVID_SOURCE || _XOPEN_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.

ERRORS

ENOMEM

Insufficient space to allocate new environment.

CONFORMING TO

SVr4, POSIX.1-2001, 4.3BSD

NOTES

The putenv() function is not required to be reentrant, and the one in libc4, libc5 and glibc 2.0 is not, but the glibc 2.1 version is.

Description for libc4, libc5, glibc: If the argument string is of the form name, and does not contain an '=' character, then the variable name is removed from the environment. If putenv() has to allocate a new array environ, and the previous array was also allocated by putenv(), then it will be freed. In no case will the old storage associated to the environment variable itself be freed.

The libc4 and libc5 and glibc 2.1.2 versions conform 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 2.0-2.1.1 differs: a copy of the string is used. On the one hand this causes a memory leak, and on the other hand it violates SUSv2. This has been fixed in glibc 2.1.2.

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 2.79 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  Copyright 1993 David Metcalfe (davidprism.demon.co.uk)

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Formatted or processed versions of this manual, if unaccompanied by
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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)