如何确定系统中是否安装了gem？

How do I find out whether a gem is installed in the system or not?

如何确定系统中是否安装了gem？

%x('gem' 'list').split.find{|i| i == "capybara"}

Is there a shorter method?

有更短的方法吗？

4 个解决方案

#1

If you're trying to do this from within ruby, you can use a built-in RubyGem method. Older versions provide a Gem.available?('capybara') method that returns a boolean, but this has been deprecated. The recommended way now is to use (assuming you're using a version that supports it):

如果您尝试在ruby中执行此操作，则可以使用内置的RubyGem方法。旧版本提供了一个返回布尔值的Gem.available？（'capybara'）方法，但这已被弃用。现在推荐的方法是使用（假设您使用的是支持它的版本）：

Gem::Specification::find_by_name('capybara')

http://rubygems.rubyforge.org/rubygems-update/Gem/Specification.html

http://rubygems.rubyforge.org/rubygems-update/Gem/Specification.html

Update

更新

If you want a boolean result, you could use .find_all_by_name() and check if the resulting array is empty:

如果需要布尔结果，可以使用.find_all_by_name（）并检查结果数组是否为空：

if Gem::Specification::find_all_by_name('capybara').any?
  # Gem is available
end

#2

%x('gem' 'list' | 'grep' 'capybara').empty?

#3

I stick this at the beginning of my Gemfile:

我坚持在我的Gemfile的开头：

def gem_available?(gemname)
  if Gem::Specification.methods.include?(:find_all_by_name) 
    not Gem::Specification.find_all_by_name(gemname).empty?
   else
     Gem.available?(gemname)
   end
 end

then just use:

然后使用：

if (gem_available?('gem_i_need'))

and everything works nicely!

一切都很好！

#4

Here's some code that works for me. It also properly handles the Gem::LoadError that gets thrown when you try to load a gem that could not be found.

这里有一些适合我的代码。它还可以正确处理当您尝试加载无法找到的gem时抛出的Gem :: LoadError。

require 'rubygems'

def can_we_find_gem(gem_name)
  found_gem = false
  begin
    found_gem = Gem::Specification.find_by_name(gem_name)
  rescue Gem::LoadError
    puts "Could not find gem '#{gem_name}'"
  else
    puts "Found gem '#{gem_name}'"
  end
end

can_we_find_gem('chef')
can_we_find_gem('not-chef')