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NetBSD 6.1.5 - man page for unsetenv (netbsd section 3)

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 conventions, 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 environment, or the string length of the
     value of name is longer than len characters, then -1 is returned and errno is set to indi-
     cate the error.

     The setenv() function inserts or resets the environment variable name in the current envi-
     ronment 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 envi-
     ronment 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; oth-
     erwise the global variable errno is set to indicate 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 buf-
			fer.

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() func-
     tion appeared in 4.3BSD-Reno.

BSD					 October 25, 2010				      BSD


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