kenv(2) [linux man page]

KENV(2)                                                       BSD System Calls Manual                                                      KENV(2)

NAME

     kenv -- kernel environment

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <kenv.h>

     int
     kenv(int action, const char *name, char *value, int len);

DESCRIPTION

     The kenv() system call manipulates kernel environment variables.  It supports the well known userland actions of getting, setting and unset-
     ting environment variables, as well as the ability to dump all of the entries in the kernel environment.

     The action argument can be one of the following:

     KENV_GET    Returns the value associated with the named kernel environment variable.  If the variable is not found, -1 is returned and the
                 global variable errno is set to ENOENT.  Only the number of bytes available in value are copied out.

     KENV_SET    Sets or adds a new kernel environment variable.  This option is only available to the superuser.

     KENV_UNSET  Unsets the kernel environment variable name.  If the variable does not exist, -1 is returned and the global variable errno is set
                 to EINVAL.  This option is only available to the superuser.

     KENV_DUMP   Dumps as much of the kernel environment as will fit in value.  If value is NULL, kenv() will return the number of bytes required
                 to copy out the entire environment.

     The name argument is the name of the environment variable to be affected.  In the case of KENV_DUMP it is ignored.

     The value argument contains either the value to set the environment variable name to in the case of KENV_SET, or it points to the location
     where kenv() should copy return data to in the case of KENV_DUMP and KENV_GET.  If value is NULL in the case of KENV_DUMP, kenv() will return
     the number of bytes required to copy out the entire environment.

     The len argument indicates how many bytes of storage value points to.

RETURN VALUES

     The kenv() system call returns 0 if successful in the case of KENV_SET and KENV_UNSET, and the number of bytes copied into value in the case
     of KENV_DUMP and KENV_GET.  If an error occurs, a value of -1 is returned and the global variable errno is set to indicate the error.

ERRORS

     The kenv() system call will fail if:

     [EINVAL]           The action argument is not a valid option, or the length of the value is less than 1 for a KENV_SET.

     [ENOENT]           no value could be found for name for a KENV_SET or KENV_UNSET.

     [EPERM]            a user other than the superuser attempted to set or unset a kernel environment variable.

     [EFAULT]           bad address was encountered while attempting to copy in user arguments, or copy out value(s).

     [ENAMETOOLONG]     the name of a variable supplied by the user is longer than KENV_MNAMELEN or the value of a variable is longer than
                        KENV_MVALLEN.

SEE ALSO

     kenv(1)

AUTHORS

     This manual page was written by Chad David <davidc@FreeBSD.org>.

     The kenv() system call was written by Maxime Henrion <mux@FreeBSD.org>.

BSD                                                               April 17, 2002                                                               BSD

GETENV(3)						   BSD Library Functions Manual 						 GETENV(3)

NAME

     getenv, getenv_r, putenv, setenv, unsetenv -- environment variable functions

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdlib.h>

     char *
     getenv(const char *name);

     int
     getenv_r(const char *name, char *buf, size_t len);

     int
     setenv(const char *name, const char *value, int overwrite);

     int
     putenv(char *string);

     int
     unsetenv(const char *name);

DESCRIPTION

     These functions set, unset and fetch environment variables from the host environment list.  For compatibility with differing environment con-
     ventions, the getenv() or getenv_r() given argument name may be appended with an equal sign ``=''.

     The getenv() function obtains the current value of the environment variable name.	If the variable name is not in the current environment, a
     NULL pointer is returned.

     The getenv_r() function obtains the current value of the environment variable name and copies it to buf.  If name is not in the current envi-
     ronment, or the string length of the value of name is longer than len characters, then -1 is returned and errno is set to indicate the error.

     The setenv() function inserts or resets the environment variable name in the current environment list.  If the variable name does not exist
     in the list, it is inserted with the given value.	If the variable does exist, the argument overwrite is tested; if overwrite is zero, the
     variable is not reset, otherwise it is reset to the given value.

     The putenv() function takes an argument of the form ``name=value'' and it will set the environment variable ``name'' equal to ``value'' by
     altering an existing entry, or creating a new one if an existing one does not exist.  The actual string argument passed to putenv() will
     become part of the environment.  If one changes the string, the environment will also change.

     The unsetenv() function deletes all instances of the variable name pointed to by name from the list.

RETURN VALUES

     The functions getenv_r(), setenv(), putenv(), and unsetenv() return zero if successful; otherwise the global variable errno is set to indi-
     cate the error and a -1 is returned.

     If getenv() is successful, the string returned should be considered read-only.

ERRORS

     [EINVAL]		The name argument to setenv() or unsetenv() is a null pointer, points to an empty string, or points to a string containing
			an ``='' character.  The value argument to setenv() is a null pointer.	The string argument to putenv() is a null pointer,
			or points to a string that either starts with a ``='' character or does not contain one at all.

     [ENOMEM]		The function setenv() or putenv() failed because they were unable to allocate memory for the environment.

     The function getenv_r() can return the following errors:

     [ENOENT]		The variable name was not found in the environment.

     [ERANGE]		The value of the named variable is too long to fit in the supplied buffer.

SEE ALSO

     csh(1), sh(1), execve(2), environ(7)

STANDARDS

     The getenv() function conforms to ANSI X3.159-1989 (``ANSI C89'').  The putenv() function conforms to X/Open Portability Guide Issue 4
     (``XPG4'').  The unsetenv() function conforms to IEEE Std 1003.1-2001 (``POSIX.1'').

HISTORY

     The functions setenv() and unsetenv() appeared in Version 7 AT&T UNIX.  The putenv() function appeared in 4.3BSD-Reno.

BSD
								 October 25, 2010							       BSD