putenv - change or add an environment variable
SYNOPSIS
#include <stdlib.h>
int putenv(char *string);
DESCRIPTION
The putenv() function adds or changes the value of envi
ronment variables. The argument string is of the form
name=value. If name does not already exist in the envi
ronment, 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 -1 if an
error occurs.
ERRORS
ENOMEM Insufficient space to allocate new environment.
NOTES
The putenv() function is not required to be reentrant, and
the one in libc4, libc5 and glibc2.0 is not, but the
glibc2.1 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 env
iron, 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 glibc2.1.2.
The BSD4.4 version, like glibc 2.0, uses a copy.
SUSv2 removes the `const' from the prototype, and so does
glibc 2.1.3.
SVID 3, POSIX, BSD 4.3
SEE ALSO
getenv(3), setenv(3), unsetenv(3), environ(5)
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