How do I use Ruby for shell scripting?

Question

I have some simple shell scripting tasks that I want to do

For example: Selecting a file in the working directory from a list of the files matching some regular e

Answer 1

As the others have said already, your first line should be

#!/usr/bin/env ruby

And you also have to make it executable: (in the shell)

chmod +x test.rb

Then follows the ruby code. If you open a file

File.open("file", "r") do |io|
    # do something with io
end

the file is opened in the current directory you'd get with pwd in the shell.

The path to your script is also simple to get. With $0 you get the first argument of the shell, which is the relative path to your script. The absolute path can be determined like that:

#!/usr/bin/env ruby
require 'pathname'
p Pathname.new($0).realpath()

For file system operations I almost always use Pathname. This is a wrapper for many of the other file system related classes. Also useful: Dir, File...

Answer 2

There's a lot of good advice here, so I wanted to add a tiny bit more.

1. Backticks (or back-ticks) let you do some scripting stuff a lot easier. Consider

   puts `find . | grep -i lib`
   

2. If you run into problems with getting the output of backticks, the stuff is going to standard err instead of standard out. Use this advice

   out = `git status 2>&1`
   

3. Backticks do string interpolation:

   blah = 'lib'
   `touch #{blah}`
   

4. You can pipe inside Ruby, too. It's a link to my blog, but it links back here so it's okay :) There are probably more advanced things out there on this topic.

5. As other people noted, if you want to get serious there is Rush: not just as a shell replacement (which is a bit too zany for me) but also as a library for your use in shell scripts and programs.

---

On Mac, Use Applescript inside Ruby for more power. Here's my shell_here script:

#!/usr/bin/env ruby
`env | pbcopy` 
cmd =  %Q@tell app "Terminal" to do script "$(paste_env)"@
puts cmd

`osascript -e "${cmd}"`

Answer 3

When you want to write more complex ruby scripts, these tools may help:

For example:

• thor(a scripting framework)

• gli(git like interface)

• methadone(for creating simple tools)

They give you a quick start to write your own scripts, especially 'command line app'.

Answer 4

Place this at the beginning of your script.rb

#!/usr/bin/env ruby

Then mark it as executable:

chmod +x script.rb

Answer 5

In ruby, the constant __FILE__ will always give you the path of the script you're running.

On Linux, /usr/bin/env is your friend:

#! /usr/bin/env ruby
# Extension of this script does not matter as long
# as it is executable (chmod +x)
puts File.expand_path(__FILE__)

On Windows it depends whether or not .rb files are associated with ruby. If they are:

# This script filename must end with .rb
puts File.expand_path(__FILE__)

If they are not, you have to explicitly invoke ruby on them, I use a intermediate .cmd file:

my_script.cmd:

@ruby %~dp0\my_script.rb

my_script.rb:

puts File.expand_path(__FILE__)

Answer 6

This might also be helpful: http://rush.heroku.com/

I haven't used it much, but looks pretty cool

From the site:

rush is a replacement for the unix shell (bash, zsh, etc) which uses pure Ruby syntax. Grep through files, find and kill processes, copy files - everything you do in the shell, now in Ruby