First Rails application - Step-by-Step Execution

Concept Flow - First Rails application

Run 'rails new app_name'

↓

Rails creates folder structure

↓

Navigate to app folder

↓

Run 'rails server'

↓

Server starts and listens

↓

Open browser at localhost:3000

↓

Rails serves default welcome page

This flow shows how to create a new Rails app, start the server, and see the default page in the browser.

Execution Sample

Ruby on Rails

rails new myapp
cd myapp
rails server

Creates a new Rails app named 'myapp', moves into its folder, and starts the Rails server.

Execution Table

Step	Command/Action	System Response	Result
1	rails new myapp	Creates app folder and files	Folder 'myapp' with Rails structure created
2	cd myapp	Changes directory	Current folder is 'myapp'
3	rails server	Starts Rails server	Server listens on http://localhost:3000
4	Open browser at http://localhost:3000	Server responds	Default Rails welcome page shown
5	Stop server (Ctrl+C)	Server stops	No longer listening on port 3000

💡 Server stops when user interrupts; app folder and files remain for development.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
Current Directory	User home	myapp created but not entered	myapp	myapp	myapp	myapp
Rails Server Status	Stopped	Stopped	Stopped	Running	Running	Stopped
Browser Page	None	None	None	None	Rails Welcome Page	None

Key Moments - 3 Insights

Why do we need to run 'cd myapp' after creating the app?

Because 'rails new' creates the app folder but does not move you inside it. You must 'cd' to run commands like 'rails server' inside the app.

What happens if you open the browser before starting the server?

The browser will not connect because the Rails server is not running yet. See step 4 in execution_table where the server must be running first.

Why does the default page show a welcome message?

Rails includes a default welcome page to confirm the server works. This is shown at step 4 when accessing localhost:3000.

Visual Quiz - 3 Questions

Look at the execution_table, what is the system response after running 'rails new myapp'?

A Starts Rails server

B Creates app folder and files

C Changes directory

D Server stops

💡 Hint

Check step 1 in the execution_table for the response to 'rails new myapp'.

At which step does the Rails server start running?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Rails Server Status' in variable_tracker and the 'System Response' in execution_table.

If you skip 'cd myapp' and run 'rails server' from the home folder, what happens?

A Error because no Rails app found

B Server starts normally

C Creates new app automatically

D Shows default welcome page

💡 Hint

Refer to key_moments about why 'cd myapp' is needed before running 'rails server'.

Concept Snapshot

rails new app_name  # creates new app folder and files
cd app_name          # move into app folder
rails server         # start Rails server
Open browser at localhost:3000 to see default welcome page
Stop server with Ctrl+C
This sets up your first Rails app ready for development.

Full Transcript

To create your first Rails application, you start by running 'rails new' with your app name. This command creates a folder with all necessary files. Next, you must change directory into the new app folder using 'cd'. Then, start the Rails server with 'rails server'. The server listens on localhost port 3000. Opening your browser to this address shows the default Rails welcome page, confirming the server runs correctly. When finished, stop the server with Ctrl+C. This process sets up your first Rails app ready for further development.

Practice

1. What command do you use to create a new Rails application folder?

easy

A. rails init myapp

B. rails new myapp

C. rails create myapp

D. rails start myapp

Solution

1. Step 1: Understand Rails app creation command

   The official command to create a new Rails app is rails new followed by the app name.

2. Step 2: Match the command with options

   Only rails new myapp uses rails new myapp, which is correct syntax.

3. Final Answer:

   rails new myapp -> Option B

4. Quick Check:

   Create app folder = rails new [OK]

Hint: Remember: 'rails new' creates the app folder [OK]

Common Mistakes:

• Using 'rails start' instead of 'rails new'
• Confusing 'rails create' with 'rails new'
• Trying 'rails init' which is not a Rails command

2. Which command starts the Rails server so you can view your app in a browser?

easy

A. rails launch

B. rails start

C. rails run

D. rails server

Solution

1. Step 1: Identify the command to run the Rails server

   The correct command to start the Rails server is rails server.

2. Step 2: Compare with options

   Only rails server matches the correct command exactly.

3. Final Answer:

   rails server -> Option D

4. Quick Check:

   Start server = rails server [OK]

Hint: Use 'rails server' to launch your app locally [OK]

Common Mistakes:

• Typing 'rails start' which is invalid
• Using 'rails run' which does not start the server
• Trying 'rails launch' which is not a Rails command

3. What will happen if you run rails new blog and then cd blog followed by rails server?

medium

A. A new Rails app named 'blog' is created and the server starts to serve it locally.

B. An error occurs because 'rails server' must be run before 'rails new'.

C. The server starts but shows a blank page because no views are created yet.

D. The command fails because 'cd blog' is not a valid Rails command.

Solution

1. Step 1: Understand the sequence of commands

   rails new blog creates a new app folder named 'blog'. cd blog moves into that folder. rails server starts the server for that app.

2. Step 2: Analyze the expected behavior

   Running these commands in order creates the app and starts the server correctly, serving the default Rails welcome page.

3. Final Answer:

   A new Rails app named 'blog' is created and the server starts to serve it locally. -> Option A

4. Quick Check:

   rails new + cd + rails server = app runs [OK]

Hint: Create app, enter folder, then start server to see app [OK]

Common Mistakes:

• Thinking 'rails server' must run before app creation
• Assuming 'cd blog' is a Rails command instead of shell
• Expecting an error when running these commands in order

4. You ran rails new myapp but when you try rails server inside the folder, you get an error. What is the most likely cause?

medium

A. You must create a controller before starting the server.

B. You need to run rails start instead of rails server.

C. You forgot to run bundle install to install dependencies.

D. The folder name 'myapp' is invalid for Rails apps.

Solution

1. Step 1: Identify common setup step after creating app

   After rails new, you usually run bundle install to install gems needed by the app.

2. Step 2: Understand error cause

   If dependencies are missing, rails server will fail to start due to missing gems.

3. Final Answer:

   You forgot to run bundle install to install dependencies. -> Option C

4. Quick Check:

   Missing gems? Run bundle install first [OK]

Hint: Run 'bundle install' after 'rails new' before starting server [OK]

Common Mistakes:

• Trying 'rails start' which is invalid
• Thinking a controller is required before server start
• Believing folder name causes the error

5. You want to create a new Rails app named shop and immediately start the server. Which sequence of commands is correct?

hard

A. rails new shop -> cd shop -> rails server

B. rails create shop -> rails server

C. rails new shop -> rails server

D. cd shop -> rails new shop -> rails server

Solution

1. Step 1: Create the app folder with correct command

   Use rails new shop to create the app folder named 'shop'.

2. Step 2: Change directory into the new app folder

   Run cd shop to move into the app folder before starting the server.

3. Step 3: Start the Rails server inside the app folder

   Run rails server to launch the app locally.

4. Final Answer:

   rails new shop -> cd shop -> rails server -> Option A

5. Quick Check:

   Create app, enter folder, start server = correct order [OK]

Hint: Create app, cd into it, then run server [OK]

Common Mistakes:

• Skipping 'cd' before running server
• Using 'rails create' which is invalid
• Running server outside app folder