Ruby script start from a specific line or method

Question

Let's say i have a script:

!#usr/bin/ruby

# step 1
puts "That's first"
# some code

#step 2
puts "That's second"
# some code

Is there a way to pass ARGV to script that will start execution from a specific line (or step, or class, or whatever)? For example executing $ ruby script.rb -s 2 will start from second step.

I have a thought about parsing the argument with if\else, but in this case script will become much more complicated and not DRY at all.

Any ideas?

Answer 1

Bad things happen when you use GOTO.

Here's a proposal that could solve your problem in a bit more elegant way :

Define your steps in 'define_steps.rb' :

# define_steps.rb
#####################################################
@steps = []

def step(i, &block)
  @steps[i] = block
end

def launch_steps!(min = 0, max = @steps.size - 1)
  @steps[min..max].each.with_index(min) do |block, i|
    if block
      puts "Launching step #{i}"
      block.call
    end
  end
end
#####################################################

step 1 do
  puts 'Step 1 with lots of code'
end

step 2 do
  puts 'Step 2 with lots of code'
end

step 3 do
  puts 'Step 3 with lots of code'
end

step 4 do
  puts 'Step 4 with lots of code'
end

Launch them separately with launch_steps.rb :

# launch_steps.rb
require_relative 'define_steps'

launch_steps!
puts "-----------------"
launch_steps!(2,3)

It outputs :

Launching step 1
Step 1 with lots of code
Launching step 2
Step 2 with lots of code
Launching step 3
Step 3 with lots of code
Launching step 4
Step 4 with lots of code
-----------------
Launching step 2
Step 2 with lots of code
Launching step 3
Step 3 with lots of code

launch_steps! without parameters runs every defined step, launch_steps!(min,max) runs every step between min and max, launch_steps!(min) runs step min and every step after.

Answer 2

Here's a program run_from_line.rb which accepts three arguments: path and start line, and end line. End line is optional and defaults to -1.

#/usr/bin/env ruby

path = ARGV.shift
program_text = File.readlines(path)
start_line = ARGV.shift.to_i;
end_line = ARGV.shift || '-1'
end_line = end_line.to_i

selected_code = program_text[start_line..end_line].join
eval selected_code

With this script at test.rb:

puts "line 0"
puts "line 1"
puts "line 2"

Testing:

> ruby run_from_line.rb test.rb 1
line 1
line 2

> ruby run_from_line.rb test.rb 1 1
line 1

If you want to make this a system-wide script, run chmod a+x run_from_line.rb then sudo mv run_from_line.rb /usr/local/sbin