PUTENV(V)           Linux Programmer's Manual           PUTENV(V)



NAME
       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.

CONFORMING TO
       SVID 3, POSIX, BSD 4.3

SEE ALSO
       getenv(v), setenv(v), clearenv(v), unsetenv(v), environ(n)



GNU                         1993-04-08                  PUTENV(V)