Ruby Reference

# puts adds a newline; print does not
puts "Hello, World!"

# Run a Ruby script
ruby main.rb

# Single-line comment

=begin
Multi-line comment block
(rarely used in practice)
=end

require 'json'           # Load from load path
require_relative 'local' # Load relative to current file

# exit(status) - default is 0
exit(1)

begin
  1 / 0
rescue ZeroDivisionError => e
  puts "Caught: #{e.message}"
ensure
  puts "Cleanup"
end

x = 10          # Local variable
@x = 10         # Instance variable
@@x = 10        # Class variable
$x = 10         # Global variable
MAX_VAL = 100   # Constant (starts with uppercase)

val = 2**128
puts val.class # Integer

"123".to_i   # String to Integer
123.to_s     # Integer to String
"1.2".to_f   # String to Float

puts "Zero is true" if 0

path = ENV['PATH']
ENV['MY_VAR'] = 'secret'

require 'date'

now = Time.now
puts now.strftime("%Y-%m-%d %H:%M:%S")

# High-resolution monotonic clock
start = Process.clock_gettime(Process::CLOCK_MONOTONIC)

a = 10 / 3      # Integer division (3)
b = 10 / 3.0    # Float division (3.333...)
c = 10 ** 2     # Power (100)
d = true && false # Logic (also: and, or, not)

if "user@example.com" =~ /@/
  puts "Match found"
end

match = "price: $100".match(/\$(\d+)/)
puts match[1] if match

require 'optparse'

options = {}
OptionParser.new do |opts|
  opts.banner = "Usage: example.rb [options]"
  opts.on("-v", "--[no-]verbose", "Run verbosely") { |v| options[:verbose] = v }
end.parse!

# Remaining positional args are in ARGV
p ARGV

def add(a, b = 0)
  return a + b # Explicit return
end

def multi
  [1, 2] # Implicit return (last expression)
end

x, y = multi # Unpacking

def modify(str)
  str << "!" # In-place modification
end

s = "hello"
modify(s)
puts s

i = 0
while i < 3
  puts i
  i += 1
end

3.times { |j| puts j }

(0..5).each do |i|
  next if i == 1 # Equivalent to 'continue'
  break if i == 3
  puts i
end

[10, 20].each { |v| puts v }

{a: 1, b: 2}.each do |key, val|
  puts "#{key}: #{val}"
end

s = "  hello  "
s.strip!      # In-place whitespace removal
s.capitalize  # "Hello"
"a-b".split("-") # ["a", "b"]

path = File.join("usr", "local", "bin")

File.open("data.bin", "rb") do |f|
  while (chunk = f.read(4096))
    # Process binary chunk
  end
end

content = File.read("file.txt")
lines = File.readlines("file.txt")

# Pack: L (uint32 LE), d (double)
data = [42, 3.14].pack("Ld")
# Unpack
val, pi = data.unpack("Ld")

a = 0b1010 & 0b1100 # AND (0b1000)
b = 0b1010 | 0b1100 # OR  (0b1110)
c = 1 << 3          # Shift (8)

"ff".hex      # 255
255.to_s(16)  # "ff"
sprintf("%02x", 255) # "ff"

require 'set'

arr = [1, 2, 3]
hash = { "key" => "value", symbol: 1 }
set = Set.new([1, 2, 2]) # {1, 2}

require 'json'

obj = JSON.parse('{"a": 1}')
json_str = JSON.generate(obj)

require 'socket'

# Client
begin
  s = TCPSocket.new('localhost', 80)
  s.puts "GET / HTTP/1.0\r\n\r\n"
  puts s.read
  s.close
rescue Errno::ECONNREFUSED
end

require 'socket'

u = UDPSocket.new
u.send("ping", 0, '127.0.0.1', 8080)

# Threads
t = Thread.new { puts "In thread" }
t.join

# Fibers (Lightweight)
f = Fiber.new { Fiber.yield "yielded" }
puts f.resume

# Ractors (Ruby 3 Parallelism - Experimental)
r = Ractor.new { "hello" }
puts r.take

require 'sqlite3'

db = SQLite3::Database.new ":memory:"
db.execute "CREATE TABLE t(id INTEGER)"
db.execute "INSERT INTO t VALUES (42)"
puts db.get_first_value "SELECT id FROM t"