Restforce

restforce.rb

require 'restforce'

# set default org with sfdx
# sfdx config set target-org=<some username or org alias>

# grab the access token & instance url from the default scratch org using sfdx
org = JSON.parse(`sfdx org display --json`)

client = Restforce.new(
            oauth_token: org['result']['accessToken'],
            instance_url: org['result']['instanceUrl'],
            api_version: '57.0'
            )     
            
puts "Username: #{org['result']['username']}"
puts "Oauth token: #{org['result']['accessToken']}"
puts '-------------------------------------'

accounts = client.query("SELECT Id, Name FROM Contact LIMIT 2")

puts accounts.first