PUTENV(3) Linux Programmer's Manual PUTENV(3)
putenv - change or add an environment variable
int putenv(char *string);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
putenv(): _SVID_SOURCE || _XOPEN_SOURCE
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.
The putenv() function returns zero on success, or nonzero if an error occurs.
ENOMEM Insufficient space to allocate new environment.
SVr4, POSIX.1-2001, 4.3BSD.
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 auto-
matic 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.
clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
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