These functions set, unset and fetch environment variables from the host environment list
. For compatibility with differing environment conventions, the given arguments
may be appended and prepended, respectively, with an equal sign "=".
function obtains the current value of the environment variable,
function inserts or resets the environment variable
in the current environment list. If the variable
does not exist in the list, it is inserted with the given
. If the variable does exist, the argument
is tested; if
is zero, the variable is not reset, otherwise it is reset to the given
function takes an argument of the form "name=value" and is equivalent to:
setenv(name, value, 1);
function deletes all instances of the variable name pointed to by
from the list.
The code below displays the current value of the PATH environment variable.
Return ValuesThe getenv function returns the value of the environment variable as a NULL-terminated string. If the variable
name is not in the current
environment, NULL is returned.
BugsSuccessive calls to setenv or putenv assigning a differently sized
value to the same
name will result in a memory leak. The FreeBSD semantics for these functions (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.
HistoryThe functions setenv and unsetenv appeared in Version 7 AT&T UNIX. The putenv function appeared in RenoBSD.