Ruby Notes and Tutorial

Rmagick - Ruby image library.

2008-07-20T06:08:00.000-07:00

I have used the Rmagick to create the gif2led, which is used for my hardware led projects. You can find more detail at http://www.bitartist.org/2008/06/gif2led-released-and-with-my-led-egg.html

It is a very simple application, and involved some manipulations on animated gif with Rmagick. The code is simple to read if you are interested in working on animated gif in Ruby.

Ping echo check in Ruby, a dummy port scanner

2008-05-22T08:14:00.000-07:00

Ping library in Ruby is fun to use,
it is easy to make it as a small port scanner

require "ping"

if ARGV.length != 3
puts "Usage: pingb machine_domain min max"
exit 0
end

for port in (ARGV[1].to_i..ARGV[2].to_i) do
if Ping.pingecho(ARGV[0],1,port) then
puts "Port #{port} open"
end
end

$ruby pingecho.rb slashdots.org 80 100
Port 80 open

Command line arguments in Ruby.

2008-05-22T07:04:00.000-07:00

Using the array: ARGV

Example:

puts "No. of arguments:" << ARGV.length.to_s

puts "Loop elements"
for options in ARGV do
puts options
end

puts "Loop index"
for i in 0..ARGV.length-1
puts "#{i} #{ARGV[i]}"
end

$ ruby testcmd.rb one two three
No. of arguments:3
Loop elements
one
two
three
Loop index
0 one
1 two
2 three

Switch case in Ruby

2008-05-22T06:58:00.000-07:00

Swith case is support in Ruby language:

i=10
case i
when 1..9
puts "not 10"
when 10
puts "it is 10"
end
output: "it is 10"

String matching:

input="hello"

case input
when "hello world"
puts "hello world"
when "hell"
puts "heaven"
when /hell/
puts "hell inside"
end

output: "hell inside"

Random Number with ruby

2008-05-21T09:25:00.000-07:00

using rand

Generate a random number in integer

rand(range in max)

for e.g.
get a random number from 1 to 10

1+rand(10)

Why need to plus "1", because rand returns 0...max-1

irb(main):034:0> 1+rand(10)
=> 8
irb(main):035:0> 1+rand(10)
=> 2
irb(main):036:0> 1+rand(10)
=> 7
irb(main):037:0> 1+rand(10)
=> 5
irb(main):038:0> 1+rand(10)
=> 1
irb(main):039:0> 1+rand(10)

Random a floating point number,
calling rand with null argument, rand returns floating number in range [0,1]

for e.g. for range 1...10
1 + rand * 9

irb(main):079:0> 1 + rand*9
=> 5.85549064689046
irb(main):080:0> 1 + rand*9
=> 8.5913031102674
irb(main):081:0> 1 + rand*9
=> 5.84003966648288
irb(main):082:0> 1 + rand*9
=> 3.45730690493765
irb(main):083:0> 1 + rand*9
=> 9.07177615052255
irb(main):084:0> 1 + rand*9
=> 5.07483813090987
irb(main):085:0> 1 + rand*9
=> 8.22263965908269

Print without newline

2008-05-21T09:22:00.000-07:00

use print for more control than puts.

irb(main):001:0> puts "Hello"
Hello
=> nil
irb(main):002:0> print "Hello"
Hello=> nil
irb(main):003:0>

Loops in Ruby (Looping...For)

2008-05-21T08:23:00.000-07:00

There are several ways to write Loops in Ruby:

1. For Loop

#print Hello World three times
For i in 1..3 do
puts "Hello World"
end

2. While / Until Loop

#print Hello World three times
i=0
while i < 3 do
puts "Hello World"
i = i + 1
end

#print Hello World three times
i=1
until i == 3 do
puts "Hello World"
i = i + 1
end

3. upto, downto and times

Every integer is an object in Ruby, and it has methods upto, downto and times.

#print Hello World three times
1.upto(3) do
puts "Hello World"
end

#print Hello World three times
3.downto(1) do
puts "Hello World"
end

#print Hello World three times
3.times do
puts "Hello World"
end

Typical Ruby File

2008-05-21T08:08:00.000-07:00

Take a look of my small Ruby file:

#!/usr/bin/ruby

#it is a comment

=begin
mutliple line comments
=end

puts "Hello World"

Notes:
- Single line comment, put "#" in the front
- Multiple line comments (use =begin...=end block) :
=begin
...comments..
=end

Ruby Hands-on

2008-05-21T00:03:00.000-07:00

It is fun to use Interative Ruby command line console to test out ruby code.

Let's do a hello world.

In your Unix/Linux or Mac OS X console,

type in

shell>irb
irb(main):001:0>

Let's do a Hello World

irb(main):001:0> puts "Hello World"
Hello World
=> nil