为何执行rails new会自动安装Rails 5.1.6而非指定的5.1.3？

Hey Ryan, I’ve run into this exact issue before—rbenv and Rails versioning can be tricky when global gems interfere with project-specific ones. Let’s break down what’s happening and fix it step by step:

Why You’re Seeing Rails 5.1.6 Instead of 5.1.3 #

• When you run rails new demo without specifying a version, it uses the latest globally installed Rails gem on your system. If you previously installed Rails 5.1.6 (even accidentally), that’s the version it’ll default to.
• When you use rails _5.1.3_ new demo, sometimes the auto-generated binstubs (the scripts in the bin/ folder) can still point to the wrong Rails version if there’s a conflict with your environment.

Step-by-Step Fixes #

1. Verify Your Rails Gem Installations #

First, check which Rails versions are installed in your current Ruby environment:

gem list rails

You should see rails (5.1.3, 5.1.6) listed. If 5.1.3 isn’t there, install it explicitly for your active Ruby version:

gem install rails -v 5.1.3

2. Ensure You’re Using the Correct Ruby Version #

Make sure you’re in the Ruby version where you installed Rails 5.1.3. Check your local project Ruby version:

rbenv local

If it’s not the right version, set it:

rbenv local <your-ruby-version> # e.g., rbenv local 2.4.2

Then re-run gem install rails -v 5.1.3 to ensure it’s installed for this Ruby version.

3. Regenerate Binstubs to Fix bin/rails about #

The most common culprit for the version mismatch in bin/rails about is outdated binstubs. Here’s how to fix it:

1. Navigate to your demo project directory:

   cd demo
   

2. Delete the existing bin/ folder:

   rm -rf bin
   

3. Regenerate the binstubs using the Rails version specified in your Gemfile:

   bundle exec rails app:update:bin
   

4. Now check the version again:

   bin/rails about
   

This should now show Rails 5.1.3.

4. Prevent Global Rails Interference (Optional) #

If you want to avoid this issue in the future, you can uninstall the global Rails 5.1.6 gem (if you don’t need it):

gem uninstall rails -v 5.1.6

Alternatively, use bundle exec for all Rails commands in your project to ensure you’re always using the version specified in your Gemfile.

Final Check #

After these steps, double-check your project’s Gemfile—it should have:

gem 'rails', '~> 5.1.3'

And your Gemfile.lock should list rails (5.1.3) instead of 5.1.6.

内容的提问来源于stack exchange，提问作者Ryan