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)

Linux man-pages 6.7                                2023-10-31                                          putenv(3)