Building out code to execute from a ruby file

Creating code to read in command line arguments

I am a very visual learner and need visual feedback when coding to “see” what the code and the data is doing. Using commands such as irb (“interactive Ruby”) in the terminal is a powerful and fast technique that helps to understand the action of a given method, what it returns and how it iteracts with data while RSpec tests really help to build out a complete and robust solution. But I really want to see how my code is working as I build out a solution in a quick and straight forward way. For example when I have a ruby class and want to run it ad-hoc with various parameters. To do this I need to create some executable code that is easily run in the terminal. Here is my guide on how to do this…..I am using my wedding calculator tool in the example

Generating an executable ruby file

If you ever want to see the list of command-line options that are available for the ruby command in the terminal you can simply type

ruby -h

To build my code and try to “get it to work” I build up the code and view effects using pp (pretty print) which will print to the terminal as I go…

  • -e command-line option that executes the code
  • ARGV creates an array from the arguments passed to your script
ruby -e 'pp ARGV'

=> []

Returns an empty array, as there are no parameters passed in.

ruby -e 'pp ARGV' 2000-01-01 2000-01-01

=> ["2000-01-01", "2000-01-01"]

Returns an array with the 2 arguments that are passed into the script.

ruby -e 'pp WeddingCalculator.half_life(wd: ARGV[0], dob: ARGV[1])' 2000-01-01 2000-01-01

=> uninitialized constant WeddingCalculator (NameError)

returns an ERROR - this prompts us to actually include the ruby class we are calling

require "wedding_calculator"

ruby -e 'require "wedding_calculator";\
  pp WeddingCalculator.half_life(wd: ARGV[0], dob: ARGV[1])' 2000-01-01 2000-01-01

=> cannot load such file -- wedding_calculator (LoadError)

ERROR ruby does not know where to find the file called wedding_calculator. Typically this is in a lib/* location and in this example it is the file lib/wedding_calculator.rb. Looking at the ruby -h options we see that

-Idirectory     specify $LOAD_PATH directory

sounds like it may help us where to load the file from, in our case replacing directory with the actual directory lib

ruby -Ilib -e 'require "wedding_calculator"; \
  pp WeddingCalculator.half_life(wd: ARGV[0], dob: ARGV[1])' 2000-01-01 2000-01-01

ruby -Ilib -e 'require "wedding_calculator"; \
   pp WeddingCalculator.half_life(wd: ARGV[0], dob: ARGV[1])' 2000-01-01 2000-01-01

=> "2000-01-01"

WOOHOO Success Now we need to take this code and store it to run anytime….

Putting the code into an executable script

Create a bin directory and run.rb file…..

mkdir bin
touch bin/run.rb

add the code solution to the run.rb file

#!/usr/bin/env ruby
# frozen_string_literal: true

# (this does the -e below)
# once off change file to exercutable for a invisible list ls -l
# chmod +x bin/run.rb

# the code solution:
#   ruby -Ilib -e 'require "wedding_calculator"; \
#     pp WeddingCalculator.half_life(wd: ARGV[0], dob: ARGV[1])' 2000-01-01 2000-01-01

$LOAD_PATH << File.join(__dir__, '..', 'lib')

require 'wedding_calculator'

pp WeddingCalculator.half_life(wed: ARGV[0], dob: ARGV[1])

# to run in terminal bin/run.rb 2000-01-01 2000-01-01

# this is my example of being able to run a ruby file in the command line

Running the new script

bin/run.rb

=> zsh: no such file or directory: bin/run.sh

which means time for some investigation, lets “List files in the long format”

ls -l bin

-rw-r--r--  1 sarahalexander  staff  313 Apr 12 17:49 run.rb

this output indicted that the files are r = readable, w = writable but no sign of any x = executable so now we need to change the state of the file to allow executable status of the file.

chmod +x bin/run.rb
  • chmod command (change mode) Modifies File Permissions and +x adds the executable state to the run.rb file and now lets check out the status…..
ls -l
-rwxr-xr-x  1 sarahalexander  staff  313 Apr 12 17:49 run.rb

WOOHOO an x!

bin/run.rb

=> nil

And yes we need to pass two arguments

bin/run.rb 2000-01-01 2000-01-01

=> "2000-01-01"

The solution appears