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(
const char *string
)
int
unsetenv(
const char *name
)
=
'',
except for
unsetenv(
).
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 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 is
equivalent to:
setenv(name, value, 1);
The
unsetenv()
function
deletes all instances of the variable name pointed to by
name
from the list.
),
setenv(
),
putenv(
),
and
unsetenv(
)
return zero if successful; otherwise 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.
EINVAL
]
name
argument to
unsetenv(
)
is a null pointer, points to an empty string, or points to a string
containing an
``
=
''
character.
ENOMEM
]
)
or
putenv(
)
failed because they were unable to allocate memory for the environment.
)
can return the following errors:
ENOENT
]
name
was not found in the environment.
ERANGE
]
)
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'') .
)
and
unsetenv(
)
appeared in
Version 7 AT&T UNIX
.
The
putenv(
)
function appeared in
4.3BSDReno.