From: Robert Klemme <shortcutter@...>
Date: 2010-02-04T20:35:05+09:00
Subject: Re: Some noob questions

On 02/04/2010 11:58 AM, John Ydil wrote:
> Hello Ruby friends!
> 
> I'm learning ruby and i already have some problems.
> 
> I have a file with Login and Ip address but not on the same line.
> Exemple :
> 
> Login1
> Address1
> Login2
> Address2
> ...
> 
> 
> I searh a way to extract the IP address when i search the login
> search.rb Login2
>> address2 
> 
> I know how to search a pattern :
> 
> Login= File.open("users" ).each_line.grep( /Login2/ )
> puts Login
> 
> First question : how can i see the line after ? the line with the Ip
> address of that login

You could use #each_slice for this (see below).

> Second question : I don't search always the same pattern so i need to
> pass an argument to my script. I tried this
> Login= File.open("users" ).each_line.grep( /ARGV[0]/ )
> puts Login
> but it doesn't show anything

You need string interpolation in the regular expression.  In your case 
the regexp will match if there is "ARGV0" somewhere in the string - 
certainly not what you wanted. :-)

If your file only contains login and password alternating you could do

def lookup(file, user)
   File.foreach(file).each_slice 2 do |name, pwd|
     name.strip!
     pwd.strip!
     return pwd if user === name
   end

   # not found
   nil
end

So, how does this work?  File.foreach(file) without a block creates an 
Enumerator, i.e. something that behaves like an Enumerable.  With 
#each_slice(2) iteration will yield two subsequent values at a time:

irb(main):012:0> (1..10).each_slice 2 do |a| p a end
[1, 2]
[3, 4]
[5, 6]
[7, 8]
[9, 10]
=> nil
irb(main):013:0>

Now we have File.foreach(file) instead of 1..10 so what happens here is 
that lines are read from the file and returned in pairs to the block. 
The block checks whether there is a match (after removing trailing 
newlines) and returns from the method if it finds something.

You can use this with regular expressions *and* Strings because of ===:

pwd = lookup "users", ARGV[0]
pwd = lookup "users", /#{ARGV[0]}/


If you want to do string matching and need to match multiple times 
during a single script execution you could as well load the file into a Hash

user_password = Hash[*(File.foreach(file).map {|s| s.chomp})]

This will work only if your file has an even number of lines though.

> Third question : After having the ip address, i need to make an ssh
> connection to this address. How can i get a variable to be usable in
> system("ssh $variable") ?

You can use regular string interpolation

system "ssh #{your_variable}"

AFAIK there is also a SSL / SSH library for Ruby.  You should probably 
look into that as well.

> Thanks for your help and sorry for my english, i hope it's
> understandable.

No problem.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/