GETENV(3) BSD Programmer's Manual GETENV(3)NAME
getenv, putenv, setenv, unsetenv - environment variable functions
SYNOPSIS
#include <stdlib.h>
char *
getenv(const char *name);
int
setenv(const char *name, const char *value, int overwrite);
int
putenv(const 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 conven-
tions, the given arguments name and value may be appended and prepended,
respectively, with an equal sign "=".
The getenv() function obtains the current value of the environment vari-
able name. If the variable name is not in the current environment, a null
pointer is returned.
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 is
equivalent to:
setenv(name, value, 1);
The unsetenv() function deletes all instances of the variable name point-
ed to by name from the list.
RETURN VALUES
The functions setenv(), putenv(), and unsetenv() return zero if success-
ful; otherwise the global variable errno is set to indicate the error and
-1 is returned.
If getenv() is successful, the string returned should be considered
read-only.
ERRORS
[ENOMEM] The function setenv() or putenv() failed because they were
unable to allocate memory for the environment.
[EINVAL] The function unsetenv() failed because the argument was a
NULL pointer, an empty string, or a string containing an
'=' character.
SEE ALSOcsh(1), sh(1), execve(2), environ(7)STANDARDS
The getenv() function conforms to ANSI X3.159-1989 ("ANSI C").
The unsetenv() function conforms to Version 3 of the Single UNIX
Specification.
HISTORY
The function getenv() appeared in Version 7 AT&T UNIX and 3BSD. The func-
tions setenv() and unsetenv() appeared in 4.3BSD-Tahoe. The putenv()
function appeared in 4.3BSD-Reno.
MirOS BSD #10-current December 11, 1993 1