Disclaimer: I am new to Ruby, and am not a professional programmer. I
work in Network Support, and have used Perl in the past for various
scripting tasks. On a lark I picked up the ‘pickaxe’ book and wanted to
try my hand at a Ruby program which will use SNMP to grab various stats
from some network devices. I am using the SNMP module
(http://snmplib.rubyforge.org/) and it’s working fine.
In this module you can do a ‘get’ or a ‘walk’ on a device - basically
the former grabs a single MIB value while the latter goes down the MIB
tree to grab multiple values at once. I wanted to be able to dynamically
call either get or walk depending on how my method was called. I know I
could get around this by just coding two separate methods or the like,
but I wanted to try to use dynamic method calls which seems to me to be
more eloquent.
Looking at the examples in the book (p. 408 in 2nd edition), it appears
I can do a .instance_method(:) assignment, then bind
that to a particular object, and then run call. For instance (from
book):
str = “cat”
ulen = String.instance_method(:length)
blen = ulen.bind(str)
blen.call → 3
How I’d like to work that in my program is to define two constants
(within a class called Device), which correspond to the two
instance_methods:
class Device
…
GET = SMTP::Manager.instance_method(:get)
WALK = SMTP::Manager.instance_method(:walk)
and then:
def query_device(mibval,type=GET,mib=RFC1213)
data = []
response = NOTSET
begin
SNMP::Manager.open(:Host => @ip.to_s,
:Community => @comm) do
|manager|
manager.load_module(mib) unless (mib == RFC1213)
mngr = type.bind(manager)
response = mngr.call(mibval)
end
rescue
etc…
end
But when I try running this, I get the following error:
uninitialized constant Device::SMTP (NameError)
It appears to be adding my class onto the method name. I do have the
necessary “require” in place (before I define the constants), and the
SNMP::Manager.open command worked fine (before I make changes to get
dynamic method calls to work). So I’m not sure why it’s adding my class
name here but it doesn’t try to do that under query_device.
If I can’t figure it out I will probably just go with passing a
parameter to query_device and use ‘catch’ to determine what method to
call, but if someone could give me a clue as to what I’m doing wrong (or
if what I’m trying to do is even possible), I’d appreciate it. Thanks.