NAME

       putenv - change or add an environment variable

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       int putenv(char *string);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       putenv():
           _XOPEN_SOURCE
               || /* glibc >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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.  On failure, it returns a nonzero value,
       and errno is set to indicate the error.

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 │
       └───────────────────────────────────────────────────┴───────────────┴─────────────────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001, SVr2, 4.3BSD-Reno.

       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 glibc 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 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, from glibc 2.0 to glibc 2.1.1, it 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.

       The 4.3BSD-Reno version, like glibc 2.0, uses a copy; this is fixed in all modern BSDs.

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

       The  GNU  C  library  implementation provides a nonstandard extension.  If string does not
       include an equal sign:

           putenv("NAME");

       then the named variable is removed from the caller's environment.

SEE ALSO

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