[Courses] [Ruby] Lesson 0: Installing, References, and your first homework assignment

[Laurel Fan]

reply to chantal

On 11/9/05, Chantal Rosmuller <chantal at antenna.nl> wrote:
> Hi I'm Chantal

Hi!

> Well anyway, here's my
> homework, some code I wrote myself, I needed to configure an interface
> on an openbsd system for a whole ip range and it had to put something
> like this:
>
> inet alias x.y.z.1 255.255.255.0
> inet alias x.y.z.2 255.255.255.0
>
> etc
>
> I didn't want to type all of that so I wrote ipspitter.rb:
> It basically takes a number to start with and adds one a number of times
> and keeps printing that, together with a string for the first three
> parts of the ip address and some text if you want

This looks great, a few comments (for you and everyone else) in-line:

> #!/usr/bin/ruby
>
> puts "This is ipspitter"
> puts "Which number do you want to start the range with?"
>
> count = gets.to_i

puts prints a string (I think it stands for "PUT String"), and gets
(conincidentally enough) gets a string.  It defaults to getting it
from standard input/output (which is the terminal if you're running
the program in the shell without redirecting input), but you can make
it put/get input from any IO object, like a file, network socket, etc
(see the IO documentation for more).

> sum = count

It doesn't look like you use sum.. maybe leftover from a previous
incarnation of the program?

> puts " How many ip addresses do you want?"
>
> number = gets.to_i
> number = number - 1
> puts "Enter the first three parts of the ip-address (for example
> 192.168.4. )"
> range = gets.chomp

Chomp is like chomp in perl;  it takes the newline off the end of the
string if it happens to have one.

> puts "Do you want to put some text in front of the ip-address? Put it here"
> textbefore = gets.chomp
>
> puts "Do you want to put some text after the ip-address? Put it here"
> textafter = gets
>
> puts textbefore + range + count.to_s + textafter
>
> number.times do
>         count +=1
>         sum += count
>         puts textbefore + range + count.to_s + textafter
> end

There are a few ways to rearrange the loop that might (or might not be) clearer.

First, if you take away the 'number = number-1' line, I think you
could also take away the first puts outside of the loop, and do:

number.times do
  puts textbefore + range + count.to_s + textafter
  count +=1
  sum += count
end

Or, you could do something like this (which we'll learn about mostly
in Lesson 2 in the Expressions chapter of the book):

start = count
end = count + number - 1
start.upto(end) do |current_number|
  puts textbefore + range + current_number.to_s + textafter
end

(I haven't tried it so there's probably an off by one error)

The upto method (in the Integer class) does the stuff in the do/end
for every integer from start up to end.

Also, a different way to create strings:  This code would do the same thing:

puts "#{textbefore}#{range}#{count}#{textafter}"

(and it would call the count.to_s for you).  We'll see this first in Lesson 1.

--
Laurel Fan
http://dreadnought.gorgorg.org