getenv man page on FreeBSD

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

     getenv, putenv, setenv, unsetenv — environment variable functions

     Standard C Library (libc, -lc)

     #include <stdlib.h>

     char *
     getenv(const char *name);

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

     putenv(char *string);

     unsetenv(const char *name);

     These functions set, unset and fetch environment variables from the host
     environment list.

     The getenv() function obtains the current value of the environment vari‐
     able, name.  The application should not modify the string pointed to by
     the getenv() function.

     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
     puts it directly into the current environment, so altering the argument
     shall change the environment.  If the variable name does not exist in the
     list, it is inserted with the given value.	 If the variable name does
     exist, it is reset to the given value.

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

     The getenv() function returns the value of the environment variable as a
     NUL-terminated string.  If the variable name is not in the current envi‐
     ronment, NULL is returned.

     The setenv(), putenv(), and unsetenv() functions return the value 0 if
     successful; otherwise the value -1 is returned and the global variable
     errno is set to indicate the error.

     [EINVAL]		The function getenv(), setenv() or unsetenv() failed
			because the name is a NULL pointer, points to an empty
			string, or points to a string containing an “=” char‐

			The function putenv() failed because string is a NULL
			pointer, string is without an “=” character or “=” is
			the first character in string.	This does not follow
			the POSIX specification.

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

     [EFAULT]		The functions setenv(), unsetenv() or putenv() failed
			to make a valid copy of the environment due to the
			environment being corrupt (i.e., a name without a
			value).	 A warning will be output to stderr with
			information about the issue.

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

     The getenv() function conforms to ISO/IEC 9899:1990 (“ISO C90”).  The
     setenv(), putenv() and unsetenv() functions conforms to IEEE Std
     1003.1-2001 (“POSIX.1”).

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

     Until FreeBSD 7.0, putenv() would make a copy of string and insert it
     into the environment using setenv().  This was changed to use string as
     the memory location of the ``name=value'' pair to follow the POSIX speci‐

     Successive calls to setenv() that assign a larger-sized value than any
     previous value to the same name will result in a memory leak.  The
     FreeBSD semantics for this function (namely, that the contents of value
     are copied and that old values remain accessible indefinitely) make this
     bug unavoidable.  Future versions may eliminate one or both of these
     semantic guarantees in order to fix the bug.

BSD				 June 20, 2007				   BSD

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