GETENV(3) OpenBSD 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(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 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
variable 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. The
memory pointed to by string becomes part of the environment and must not
be deallocated by the caller. If the variable already exists, it will be
overwritten. A common source of bugs is to pass a string argument that
is a locally scoped string buffer. This will result in corruption of the
environment after leaving the scope in which the variable is defined.
For this reason, the setenv() function is preferred over putenv().
The unsetenv() function deletes all instances of the variable name
pointed to by name from the list.
RETURN VALUES
These functions return zero if successful; 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
[EINVAL] The setenv() or unsetenv() function was passed a name
containing an `=' character.
The unsetenv() function was passed an empty name or a NULL
pointer.
The putenv() function was passed a string that did not
contain an `=' character.
[ENOMEM] The setenv() or putenv() function failed because it was
unable to allocate memory for the environment.
SEE ALSOcsh(1), sh(1), execve(2), environ(7)STANDARDS
The getenv() function conforms to ANSI X3.159-1989 (``ANSI C'').
HISTORY
The function getenv() appeared in Version 7 AT&T UNIX and 3BSD. The
functions setenv() and unsetenv() appeared in 4.3BSD-Tahoe. The putenv()
function appeared in 4.3BSD-Reno.
OpenBSD 4.9 July 6, 2010 OpenBSD 4.9
