Ruby中UTC与本地时区问题咨询（ET时区Mac OSX环境）

Hey there! Since you're on Mac OSX in the Eastern Time (ET) zone (UTC-4) and curious about Ruby's timezone behavior, let's break down the key ways to configure this properly:

1. Temporary Session-Level Timezone Setup #

If you just want to test a timezone change for your current terminal session, setting the TZ environment variable works exactly like the example you saw. For your ET timezone, use the identifier America/New_York:

# Check current TZ value
ENV["TZ"] #=> nil (default state)

# Set to Eastern Time
ENV["TZ"] = "America/New_York"
# Verify the change
Time.now #=> Will show current time in ET (UTC-4 or UTC-5 depending on daylight saving)

This change only lasts until you close the terminal window.

2. Permanent User-Level Timezone Setup #

To make the timezone stick across all your terminal sessions on Mac:

• Open your shell configuration file (either ~/.zshrc for Zsh, the default on newer Macs, or ~/.bash_profile for Bash).
• Add this line at the end:

  export TZ="America/New_York"
  

• Save the file and reload it with:

  source ~/.zshrc # or source ~/.bash_profile
  

Now every new Ruby process you run in the terminal will use ET by default.

3. Project-Specific Timezone Configuration #

If you don't want to change the global timezone and only want a specific Ruby project to use ET, use the tzinfo gem (it's often included with Rails, but you can add it to standalone projects too):

First, add it to your Gemfile if using Bundler:

gem 'tzinfo'

Then use it in your code:

require 'tzinfo'

# Get the Eastern Timezone object
et_timezone = TZInfo::Timezone.get('America/New_York')

# Get current time in ET
current_et_time = et_timezone.now

# Convert a UTC time to ET
utc_time = Time.utc(2024, 5, 20, 14, 0, 0)
et_time = et_timezone.utc_to_local(utc_time)

A Quick Note on Default Behavior #

You mentioned the example showed Ruby using UTC when TZ is nil—but on Mac OSX, if you don't set TZ, Ruby will actually respect your system's configured timezone (which you've set to ET). That example might have been from a server environment (like Linux) where the system default timezone is UTC by default. To confirm your system timezone in Ruby without setting TZ, just run Time.now—it should show your local ET time.

内容的提问来源于stack exchange，提问作者Daniel Viglione