I'm trying to use rake in my ruby script...(Ruby 1.8.6, JRuby 1.6.5)
Downloaded rake using gem install --remote rake, looks ok on install...
Fetching: rake-0.9.2.2.gem (100%)
Successfully installed rake-0.9.2.2
1 gem installed
I've got a simple ruby script which works fine, but when I import rake to using any of the following requires, it starts complaining....
require 'rake'
LoadError: no such file to load -- rake
or
require '/lib/rake'
LoadError: no such file to load -- lib/rake
After some searching, I found that adding require 'rubygems' just before rakefixes the issue....
require 'rubygems'
require 'rake'
Even though it's working, I've got some questions...
The gem spec on rake shows the require_path as lib, so why
doesn't require '/lib/rake' work? Am I misunderstanding the significance of require_path?
Why is it necessary to place require 'rubygems' before require
'rake'
Yes, you are misunderstanding the significance. The require_paths in the specification is an array of subdirectories of that gem's installation directory that should be searched for files belonging to the gem.
To find out where rake really is, try this:
$ gem which rake
You'll see that it is actually installed somewhere completely unrelated to /lib; on my system, it's under /var/lib/gems. Ruby gems, in general, live in their own directory structure; the only file in the standard Ruby include path ($:) is rubygems itself, which you used to have to explicitly require in order to make any actual gems visible. (Since Ruby 1.9, that has not been necessary.)
Gems are more complex than just libraries to load; you can have multiple versions of the same gem installed, and specify which one you want at a time, and do other things that wouldn't work if the gems were just dumped into the standard Ruby include path.
The require_path in the gemspec tells ruby where the files of this gem are located within the gem. It makes you able to type require 'rake', and ruby then knows it needs to look for /lib/rake within the gem installation folder.
In Ruby 1.8, rubygems (the mechanism responsible for making gems available to your app) is not loaded by default, and the default ruby isn't aware of any gem on your system. You need to load rubygems before being able to require any other gem. This is not the case anymore with Ruby 1.9.
Related
I noticed for some gems you must include it in the file where you want to use it like this require 'a_gem', but this is not always the case.
I am going to compose a gem by myself. What should I do if I do not want to add the require 'my_gem' to the .rb file when using it?
Usually, an application that is using a gem needs to require the gem:
require "my_awesome_gem"
MyAwesomeGem.do_something_great
However, if an application is using bundler, which defines the application's gem in a file called "Gemfile":
source 'http://rubygems.org'
gem 'my_awesome_gem'
then the application may invoke bundler in a way that automatically requires all of the gems specified in the Gemfile:
require "bundler"
Bundler.require
MyAwesomeGem.do_something_great
Rails projects use Bundler.require, so a Rails application will not need to explicitly require a gem in order to use it: Just add the gem to the Gemfile and go.
For more about Bundler.require, see the bundler documentation
For more about how Rails uses Bundler, see How Does Rails Handle Gems? by Justin Weiss.
This doesn't make sense. If you want to write a Gem and use it, it needs to be required somewhere.
This "somewhere" could be explicit in one of your scripts, it could be written in a Gemfile or it could be required by another script/gem that is required by your script.
If you write a gem, Ruby will not include it automatically in all your scripts.
Finally, if you publish it, should every single Ruby script on earth magically require it and execute your code?
I suppose that the project you have seen which didn't use require 'a_gem' was using a Gemfile.
I'm writing a batch script as a setup for a ruby program I'm writing. It needs to be able to
a. Make sure Ruby is installed on the user's computer (and if not point them to the ruby download page)
b. make sure the ruby "yaml" gem is installed, which is a prerequisite for it. I've tried
gem install yaml
in the batch script to no avail. How can I write a batch script that will do these two things?
As far as I know, there is no yaml gem. Although it must be required in code that uses it, it is distributed as part of a Ruby installation. Try this:
ruby -ryaml -e"puts 'YAML found'"
It should work; and if you change the -r token to some nonexistent gem, you'll see an exception raised.
Instead of writing your own script, you could use bundler and create a gemfile. This way people can install all the gems on any operating system.
Example:
require 'rubygems'
require 'bundler/setup'
require 'nokogiri'
require 'rest-client'
#require all your gems like normal
def parse(site)
Nokogiri::HTML(RestClient.get(site))
end
And for the gem file:
source: "https://rubygems.org"
gem 'nokogiri', '~> 1.6.7.2' #<= you can specify which version
gem 'rest-client' #<= you don't have to specify a version though
After you've got everything set up, cd to the directory that has the gemfile and run bundle install this will install all the gems
So, I've created a GitHub to manage my latest Ruby project, and I want for it to utilize a couple of gems. On my PC, all I have to go is type
gem install "gemName"
and it loads it to my computer, and then all I have to do in my Ruby script is have
require "rubygems"
require "gemName"
How can I do this with GitHub? What I tried to do is create a subfolder from the main repository (called "RubyGems") and then in my main ruby script
require "/RubyGems/colorize"
require "/Rubygems/psych"
With the two gems (colorize and psych) in the "RubyGems" folder.
Is this the proper way to do this? Will this even work? What is the right way to do this? (Sorry, I'm kinda new to GitHub.)
A couple of things, unless you're using a really old version of Ruby (like 1.9) you don't need to require 'rubygems' because is already required by default, next I highly recommend you to get familiar with bundler.
Bundler is used for "bundling" the required gems you use, to so do you have to install the gem (gem install bundler) and then you create a Gemfile, like this:
source 'https://rubygems.org'
ruby '2.2.0'
gem 'colorize', git: 'https://github.com/fazibear/colorize.git'
gem 'psych'
Execute bundle install after, that will create Gemfile.lock file, make sure you push both files to your repository.
With that you would be able to bundle exec ./your-script.rb, assuming your script is something like this:
require 'psych'
require 'colorize'
# Here I do stuff with psych and colorize
I use:
rvm 1.25.19 (stable)
ruby 1.9.3p545
I install gem rake command
gem install rake
I understand that $LOAD_PATH should contain the paths:
~/.rvm/rubies/ruby1.9/gems/rake/lib
~/.rvm/rubies/ruby1.9/gems/rake/bin
I execute command:
ruby -e 'puts $LOAD_PATH'
output:
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/site_ruby/1.9.1
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/site_ruby/1.9.1/x86_64-linux
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/site_ruby
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/vendor_ruby/1.9.1
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/vendor_ruby/1.9.1/x86_64-linux
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/vendor_ruby
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/1.9.1
/home/slip/.rvm/rubies/ruby-1.9.3-p545/lib/ruby/1.9.1/x86_64-linux
why path to gem 'rake' don't add?
Installing a gem in Ruby doesn’t automatically add that gem’s files to the load path. When you require a file, first the existing load path is searched and if no matching file is found then Rubygems searches the installed gems for the file. If such a gem is found, then it is activated, which is when the gem’s lib directory is added to the load path.
Here’s an example using the Haml gem:
puts "Before:"
puts $LOAD_PATH
puts
require 'haml'
puts "After:"
puts $LOAD_PATH
This produces:
Before:
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/site_ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/site_ruby/1.9.1/x86_64-darwin10.8.0
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/site_ruby
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/vendor_ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/vendor_ruby/1.9.1/x86_64-darwin10.8.0
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/vendor_ruby
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/1.9.1/x86_64-darwin10.8.0
After:
/Users/matt/.rvm/gems/ruby-1.9.3-p448/gems/tilt-1.4.1/lib
/Users/matt/.rvm/gems/ruby-1.9.3-p448/gems/haml-4.0.5/lib
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/site_ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/site_ruby/1.9.1/x86_64-darwin10.8.0
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/site_ruby
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/vendor_ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/vendor_ruby/1.9.1/x86_64-darwin10.8.0
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/vendor_ruby
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/1.9.1/x86_64-darwin10.8.0
See how the lib directories for Tilt (which is a dependency of Haml) and Haml have been added to the start of the load path.
In the case of some gems, such as Rake, this is complicated by the fact they are part of the standard library and so are already on the load path. If you changed the example above to use require 'rake' then you wouldn’t see any change in the load path. In this situation you can specify you want to use the gem version with the gem method. This activates the gem in question, placing its lib directory at the start of the load path so when you later call require you will load the correct version.
For example, this script
require 'rake'
puts Rake::VERSION
produces 0.9.2.2 with Ruby 1.9.3, as that is the version of Rake included in the standard library. However this script:
gem 'rake'
require 'rake'
puts Rake::VERSION
produces 10.1.1, since that is the current highest version of the Rake gem installed on my system. You can also specify a particular gem version by providing a second argument to gem (this is the same syntax as used in Gemfiles). Note that the gem method doesn’t require any files, you have to do that as a separate step.
I think I have a basic understanding of what require/include statements at the top of a ruby script are doing, like
require 'rspec'
These statements are easy to google and find relevant results. But sometimes I have seen a gem statement like
gem 'rspec'
What does this line do?
In ruby code, gem(gem_name, *requirements) defined in Kernel tells Ruby to load a specific version of gem_name. That's useful when you have installed more than one version of the same gem.
For example, if you have installed two versions of rspec, say 2.12.0 and 2.13.0, you can call gem before require to use specific version. Note that gem should come before the require call.
gem 'rspec', '=2.12.0'
require 'rspec'
A gem 'gem_name' without version uses the latest version on your machine, and that's unnecessary. You can call require without gem to get the same behavior.
And besides, in Bundler::Dsl, gem is used to tell bundler to prepare/install specific version of ruby gems. You'll see that in Gemfile
The original behaviour of require, before Rubygems, was to search all the directories listed in the $LOAD_FILES variable for the file, and to load the first one it finds that matches. If no matching file was found, require would raise a LoadError.
Rubygems changes this process. With Rubygems, require will search the existing $LOAD_PATH as before, but if there is no matching file found then Rubygems will search the installed gems on your machine for a match. If a gem is found that contains a matching file, that gem is activated, and then the $LOAD_PATH search is repeated. The main effect of activating a gem is that the gems lib directory is added to your load path. In this way the second search of the load path will find the file being required.
Normally this will mean that the latest version of a gem that you have installed gets activated. Sometimes you will want to use a different version of a gem, and to do that you can use the gem method. The gem method activates a gem, and you can specify the version you want, but doesn’t require any files. When you later require the files you want, you’ll get them from the gem version you specified.
In Ruby, gems are packages with functionality that can be used out of the box (as libraries in other Programming languages).
The gems that you use with your Ruby Project can easily be managed with a tool called "bundler", just google it. The snippet of code you posted is part of the spec file that bundler uses to install and update all the libraries that you specify for your project.
If you are developing a Ruby on Rails, using gems an managing them with bundler is very common and so to say best practice.
Gems are just great because there are so many useful libraries that extend default functionality, eg of rails, and that you can use out of the box!
For a list of gems, visit rubygems.org