From: Derek Smith <derekbellnersmith@...>
Date: 2009-08-20T08:49:58+09:00
Subject: Re: if defined on var

Sebastian Hungerecker wrote:
> Am Mittwoch 19 August 2009 04:22:18 schrieb Derek Smith:
>> My goal is to see if a table exists by testing the var holding the data
>> is true/defined or not.  Will you help?
> 
> true and defined are two very different things. Take this snippet as an
> example:
> 
> x = 42
> y = false
> z = nil
> 
> Here the variables x, y and z are defined. The variables a, b and 
> foobarbaz
> are not. In short: once you assign a value to a variable that variable 
> is
> defined - no matter whether that value was true or not. If you want to 
> check
> whether the value a variable holds is true or not, do that. Don't use
> defined?.
> In your case you can just do  if table_exists  which even reads more
> naturally.
> 
> HTH,
> Sebastian

Hey Seb,

Your advice is always welcome and respected.  But Iam still confused, 
see below.
The table derek does NOT exist of course.

table_exists = db.execute("select name from sqlite_master where 
type='table' and tbl_name='derek'")

if table_exists
   p "yes", "#{table_exists}"
end
if table_exists == ""
    p "yes"
else
    p "no"
end

__OUTPUT__

$ ruby mail_log_miner.rb
"yes"
""
"no"

With a table that does exist using same if clauses.

ruby mail_log_miner.rb
"yes"
"lines"
"no"

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