PUTENV(3)                   Linux Programmer's Manual                  PUTENV(3)

       putenv - change or add an environment variable

       #include <stdlib.h>

       int putenv(char *string);

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

               || /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _SVID_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.  On failure, it returns a
       nonzero value, and errno is set to indicate the error.

       ENOMEM Insufficient space to allocate new environment.

       For an explanation of the terms used in this section, see attributes(7).

       │Interface                         Attribute     Value               │
       │putenv()                          │ Thread safety │ MT-Unsafe const:env │

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

       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 version 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, glibc versions 2.0 to
       2.1.1 differ: 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 4.4BSD version, like glibc 2.0, uses a copy.

       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:


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

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

       This page is part of release 5.12 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

GNU                                2021-03-22                          PUTENV(3)