To install a ruby gem, enter the command:
gem install [gemname]
If you are working on a project with a list of gem dependencies, then these will be listed in a file named
Gemfile. To install a new gem in the project, add the following line of code in the
Gemfile is used by the Bundler gem to install dependencies your project requires, this does however mean that you'll have to install Bundler first by running (if you haven't already):
gem install bundler
Save the file, and then run the command:
The version number can be specified on the command live, with the
-v flag, such as:
gem install gemname -v 3.14
When specifying version numbers in a
Gemfile, you have several options available:
gem 'gemname')-- Will install the latest version which is compatible with other gems in the
gem 'gemname', '3.14') -- Will only attempt to install version
3.14(and fail if this is incompatible with other gems in the
gem 'gemname', '>=3.14') -- Will only attempt to install the latest version which is compatible with other gems in the
Gemfile, and fails if no version greater than or equal to
3.14is compatible. The operator
>can also be used.
gem 'gemname', '~>3.14') -- This is functionally equivalent to using
gem 'gemname', '>=3.14', '<4'. In other words, only the number after the final period is permitted to increase.
As a best practice: You might want to use one of the Ruby version management libraries like rbenv or rvm. Through these libraries, you can install different versions of Ruby runtimes and gems accordingly. So, when working in a project, this will be especially handy because most of the projects are coded against a known Ruby version.
You can install a gem from github or filesystem. If the gem has been checked out from git or somehow already on the file system, you could install it using
gem install --local path_to_gem/filename.gem
Installing gem from github. Download the sources from github
mkdir newgem cd newgem git clone https://urltogem.git
Build the gem
gem build GEMNAME.gemspec gem install gemname-version.gem
To check if a required gem is installed, from within your code, you can use the following (using nokogiri as an example):
begin found_gem = Gem::Specification.find_by_name('nokogiri') require 'nokogiri' .... <the rest of your code> rescue Gem::LoadError end
However, this can be further extended to a function that can be used in setting up functionality within your code.
def gem_installed?(gem_name) found_gem = false begin found_gem = Gem::Specification.find_by_name(gem_name) rescue Gem::LoadError return false else return true end end
Now you can check if the required gem is installed, and print an error message.
if gem_installed?('nokogiri') require 'nokogiri' else printf "nokogiri gem required\n" exit 1 end
if gem_installed?('nokogiri') require 'nokogiri' else require 'REXML' end
Gemfile is the standard way to organize dependencies in your application. A basic Gemfile will look like this:
source 'https://rubygems.org' gem 'rack' gem 'sinatra' gem 'uglifier'
You can specify the versions of the gem you want as follows:
# Match except on point release. Use only 1.5.X gem 'rack', '~>1.5.2' # Use a specific version. gem 'sinatra', '1.4.7' # Use at least a version or anything greater. gem 'uglifier', '>= 1.3.0'
You can also pull gems straight from a git repo:
# pull a gem from github gem 'sinatra', git: 'https://github.com/sinatra/sinatra.git' # you can specify a sha gem 'sinatra', git: 'https://github.com/sinatra/sinatra.git', sha: '30d4fb468fd1d6373f82127d845b153f17b54c51' # you can also specify a branch, though this is often unsafe gem 'sinatra', git: 'https://github.com/sinatra/sinatra.git', branch: 'master'
You can also group gems depending on what they are used for. For example:
group :development, :test do # This gem is only available in dev and test, not production. gem 'byebug' end
You can specify which platform certain gems should run on if you application needs to be able to run on multiple platforms. For example:
platform :jruby do gem 'activerecord-jdbc-adapter' gem 'jdbc-postgres' end platform :ruby do gem 'pg' end
To install all the gems from a Gemfile do:
gem install bundler bundle install
Sometimes you need to make a script for someone but you are not sure what he has on his machine. Is there everything that your script needs? Not to worry. Bundler has a great function called in line.
It provides a
gemfile method and before the script is run it downloads and requires all the necessary gems. A little example:
require 'bundler/inline' #require only what you need #Start the bundler and in it use the syntax you are already familiar with gemfile(true) do source 'https://rubygems.org' gem 'nokogiri', '~> 22.214.171.124' gem 'ruby-graphviz' end