Some noob questions

Ruby
1

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

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

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”) ?

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

Ydil

2

Thanks for the explanation Robert, I will try this.

3

On 02/04/2010 11:58 AM, John Y. wrote:

Address2
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. :slight_smile:

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

4

On Thu, Feb 4, 2010 at 5:35 AM, Robert K.
[email protected]wrote:

The book “Practical Ruby Gems” suggests net-ssh (
RubyGems.org | your community gem host), and has a six page example of a
simple
use program that logs onto a remote server with SSH and uses Vim to edit
a
text file. It also has an example of net-sftp. (though one of those was
outdated, I think the net-sftp version had changed)

5

Robert K. wrote:

File.foreach(file).each_slice 2 do |name, pwd|

How is it better than ‘File.open(file).each_slice’ ?

6

On 05.02.2010 00:10, Albert S. wrote:

Robert K. wrote:

File.foreach(file).each_slice 2 do |name, pwd|

How is it better than ‘File.open(file).each_slice’ ?

It closes the file handle properly which your variant doesn’t do.

Kind regards

robert

7

John Y. wrote:

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”) ?

That would be either
system(“ssh”,variable) # you split the args
or
system(“ssh #{variable}” # shell splits the args

But this is probably not what you want, unless you’re just using ssh to
execute a single command remotely, and you’re using RSA keys so you’re
not going to be prompted for a passwords.

Have a look at Net::SSH and Net::SSH::Telnet (the latter wraps Net::SSH
in an API which is a drop-in replacement for Net::Telnet)

8

Robert K. wrote:

On 05.02.2010 00:10, Albert S. wrote:

Robert K. wrote:

File.foreach(file).each_slice 2 do |name, pwd|

How is it better than ‘File.open(file).each_slice’ ?

It closes the file handle properly which your variant doesn’t do.

You mean, that in my version the file isn’t closed till the file object
gets destroyed by the garbage collector?

I see.

(I assume the enumerator returned by foreach() mimics foreach()'s
behaviour; that is, that it closes the file after the last iteration.)

9

Josh C. wrote:

On Thu, Feb 4, 2010 at 5:35 AM, Robert K.
[email protected]wrote:

The book “Practical Ruby Gems” suggests net-ssh (
RubyGems.org | your community gem host), and has a six page example of a
simple
use program that logs onto a remote server with SSH and uses Vim to edit
a
text file. It also has an example of net-sftp. (though one of those was
outdated, I think the net-sftp version had changed)

Thanks for your help but the ssh command was an exemple :stuck_out_tongue:

In fact, i need to check routes on a linux router. It’s a light linux
distribution, i can’t install anything.
There is ruby 1.8.2 inside that’s why i’m learning how to use it.

New question !

Thanks to Robert, I have my IP address (Youhou) I need to check the
route with this IP address.

the linux command is “ip route get {IP address}”
so my command is : system(“ip route get #{ipaddress}”) but the result of
this, is just true or false. How can I put the result of my command in a
variable ?

regards,

Ydil

10

On 02/05/2010 12:50 PM, Albert S. wrote:

Robert K. wrote:

On 05.02.2010 00:10, Albert S. wrote:

Robert K. wrote:

File.foreach(file).each_slice 2 do |name, pwd|

How is it better than ‘File.open(file).each_slice’ ?
It closes the file handle properly which your variant doesn’t do.

You mean, that in my version the file isn’t closed till the file object
gets destroyed by the garbage collector?

Exactly.

I see.

(I assume the enumerator returned by foreach() mimics foreach()'s
behaviour; that is, that it closes the file after the last iteration.)

It does not mimic the behavior, it uses it!!

irb(main):001:0> class X
irb(main):002:1> def self.foreach
irb(main):003:2> if block_given?
irb(main):004:3> puts “open”
irb(main):005:3> yield 123
irb(main):006:3> puts “close”
irb(main):007:3> else
irb(main):008:3* Enumerator.new(self, :foreach)
irb(main):009:3> end
irb(main):010:2> end
irb(main):011:1> end
=> nil
irb(main):012:0> X.foreach {|x| p x}
open
123
close
=> nil
irb(main):013:0> X.foreach.map {|x| x + 10000}
open
close
=> [10123]
irb(main):014:0>

Kind regards

robert

11

Robert K. wrote:

On 02/05/2010 12:50 PM, Albert S. wrote:

Robert K. wrote:

On 05.02.2010 00:10, Albert S. wrote:

Robert K. wrote:

File.foreach(file).each_slice 2 do |name, pwd|

How is it better than ‘File.open(file).each_slice’ ?
It closes the file handle properly which your variant doesn’t do.

You mean, that in my version the file isn’t closed till the file object
gets destroyed by the garbage collector?

Exactly.

I see.

(I assume the enumerator returned by foreach() mimics foreach()'s
behaviour; that is, that it closes the file after the last iteration.)

It does not mimic the behavior, it uses it!!

irb(main):002:1> def self.foreach
irb(main):003:2> if block_given?
[…]
irb(main):007:3> else
irb(main):008:3* Enumerator.new(self, :foreach)
irb(main):009:3> end
irb(main):010:2> end

Nice. Pheeew, I still have a long road to walk before I acquire the
“Ruby way of thinking”.

Robert, thanks. Whenever I read your answers here, even to the most
trivial questions, I’m treated to some eye-opening gems.

I’m generally aware of the power of Ruby, but oftentimes it seems to me
unleashing it would involve a few lines of code, whereas you do it
easily in just one line of it.

12

On Fri, Feb 5, 2010 at 3:59 AM, John Y. [email protected] wrote:

the linux command is “ip route get {IP address}”
so my command is : system(“ip route get #{ipaddress}”) but the result of
this, is just true or false. How can I put the result of my command in a
variable ?

You can use %x( … ) for this, those parentheses can also be things
like
brackets or pipes, even @ symbols. So, for example:

dir_list = %x(ls -l)
puts “The directory’s listing is:”
puts dir_list

13

On 02/05/2010 02:01 PM, Albert S. wrote:

Exactly.
irb(main):007:3> else
irb(main):008:3* Enumerator.new(self, :foreach)
irb(main):009:3> end
irb(main):010:2> end

Nice. Pheeew, I still have a long road to walk before I acquire the
“Ruby way of thinking”.

Hmm, maybe it helps that I practice a Japanese martial art. :wink:

Robert, thanks. Whenever I read your answers here, even to the most
trivial questions, I’m treated to some eye-opening gems.

You’re welcome! I’m glad that I could help. I am always amazed how
friendly our community is compared to others and I try to maintain that
by sharing what I believe to have understood about the language.

I’m generally aware of the power of Ruby, but oftentimes it seems to me
unleashing it would involve a few lines of code, whereas you do it
easily in just one line of it.

Well, it might look easy but of course I don’t post all the failed tests
and attempts that end in dead end streets in order to not distract from
the content I want to convey. :slight_smile:

Kind regards

robert

14

2010/2/8 Aldric G. [email protected]:

Hmm, maybe it helps that I practice a Japanese martial art. :wink:

Not to completely derail the conversation here (oops?) but, as a
parenthesis… Which one?

Kind regards

robert

15

Robert K. wrote:

On 02/05/2010 02:01 PM, Albert S. wrote:

Exactly.
irb(main):007:3> else
irb(main):008:3* Enumerator.new(self, :foreach)
irb(main):009:3> end
irb(main):010:2> end

Nice. Pheeew, I still have a long road to walk before I acquire the
“Ruby way of thinking”.

Hmm, maybe it helps that I practice a Japanese martial art. :wink:

Not to completely derail the conversation here (oops?) but, as a
parenthesis… Which one?

16

John Y. wrote:

File.foreach(“/etc/raddb/users”).each_slice 4 do |name, ip, dump, table|
puts name.strip!
puts ip.strip!
puts table.strip!
end

here is the file /etc/raddb/users

login Auth-Type :=Local, User-Password == “bonjour”
Framed-IP-Address = ipaddress,
Fall-Through = No
# table 254

Here is the error :
./test.rb:12:in `foreach’: no block given (LocalJumpError)
from ./test.rb:12

I wonder if it’s due to the difference between the 2 versions, Do you
have an idea ?

Well, for this one, a quick look at the documentation will give you the
answer:
http://ruby-doc.org/core/classes/IO.html#M002243

“foreach” expects a block. So you can’t really do “each slice” on
“foreach” since you should do “foreach” on … er … each line in the
file.
Probably you’ll do the foreach, and a slice on that line within the code
block instead.

17

Hi, me again…

As i said before, I “play” with ruby on a light linux (ruby 1.8.2).
I made my script on my computer (ruby 1.8.7) and move it to my linux.

I works fine on my computer but an error occured when i launch it on my
linux.

Here is my code :

File.foreach("/etc/raddb/users").each_slice 4 do |name, ip, dump, table|
puts name.strip!
puts ip.strip!
puts table.strip!
end

here is the file /etc/raddb/users

login Auth-Type :=Local, User-Password == “bonjour”
Framed-IP-Address = ipaddress,
Fall-Through = No
# table 254

Here is the error :
./test.rb:12:in `foreach’: no block given (LocalJumpError)
from ./test.rb:12

I wonder if it’s due to the difference between the 2 versions, Do you
have an idea ?

18

2010/2/11 Aldric G. [email protected]:

login Auth-Type :=Local, User-Password == “bonjour”
have an idea ?

Well, for this one, a quick look at the documentation will give you the
answer:
class IO - RDoc Documentation

“foreach” expects a block. So you can’t really do “each slice” on
“foreach” since you should do “foreach” on … er … each line in the
file.
Probably you’ll do the foreach, and a slice on that line within the code
block instead.

He’s on 1.8.2. There you have to do

require ‘enumerator’

File.to_enum(:foreach, “/etc/raddb/users”).each_slice 4 do |name, ip,
dump, table|
puts name.strip!
puts ip.strip!
puts table.strip!
end

The convenient feature to return an Enumerator from enumerating
methods which expect a block but do not receive it was added in 1.9
and backported to 1.8.7.

Kind regards

robert

19

Robert K. wrote:

2010/2/11 Aldric G. [email protected]:

login Auth-Type :=Local, User-Password == “bonjour”
have an idea ?

Well, for this one, a quick look at the documentation will give you the
answer:
class IO - RDoc Documentation

“foreach” expects a block. So you can’t really do “each slice” on
“foreach” since you should do “foreach” on … er … each line in the
file.
Probably you’ll do the foreach, and a slice on that line within the code
block instead.

He’s on 1.8.2. There you have to do

require ‘enumerator’

File.to_enum(:foreach, “/etc/raddb/users”).each_slice 4 do |name, ip,
dump, table|
puts name.strip!
puts ip.strip!
puts table.strip!
end

The convenient feature to return an Enumerator from enumerating
methods which expect a block but do not receive it was added in 1.9
and backported to 1.8.7.

Kind regards

robert

I was afraid of this, but :
./test.rb:5:in `require’: No such file to load – enumerator (LoadError)
from ./test.rb:5

Maybe I haven’t the full ruby because it’s a small linux…

20

2010/2/11 John Y. [email protected]:

“foreach” since you should do “foreach” on … er … each line in the
puts name.strip!
from ./test.rb:5

Maybe I haven’t the full ruby because it’s a small linux…

Oooops! Sorry for the wrong advice. Either that or Enumerator did
not exist in 1.8.2 (which is ancient btw - I cannot remember having
used it).

Kind regards

robert