CheatRuby Scripting language
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Start here
ruby -e '<code>'
Run a one-liner
ruby <file>.rb
Run a script
irbInteractive console
ruby -c <file>.rb
Check syntax only
ruby -w <file>.rb
Run with warnings
gem install <name>
Install a gem
ruby -n -e '<code>'
Loop over input lines
bundle exec <cmd>
Run with the Gemfile gems
Concepts
- Input line stdin or files
- $_ current line
- Output -p prints $_
Running ruby
ruby -e '<code>'
Execute code from the command line
ruby <file>.rb [args]
Run a script (args in ARGV)
ruby -vPrint version, enable verbose mode
ruby -c <file>.rb
Syntax check only
ruby -w <file>.rb
Enable warnings
ruby -r <lib> -e '<code>'
Require a library first
ruby -I <dir> <file>.rb
Add a dir to the load path
ruby -n -e '<code>'
Run code for each input line
ruby -p -e '<code>'
Like -n, then print each line
ruby -lane 'puts $F[0]'
Split lines into fields in $F
ruby -i.bak -pe '<code>' <file>
Edit files in place with backup
irb
irbStart the console
ls <obj>List methods and variables of an object
show_doc <Class#method>
Show documentation inline
show_source <Class#method>
Show a method's source
binding.irbBreakpoint: open irb at this line
Gems
gem install <name>
Install a gem
gem install <name> -v <version>
Install a specific version
gem install <name> --user-install
Install into your home dir
gem listList installed gems
gem search <regexp>
Search remote gems
gem uninstall <name>
Remove a gem
gem outdatedList gems with newer versions
gem update <name>
Update a gem
Syntax
puts <x>Print with a newline
p <x>Print inspect form, returns the value
name = "#{first} #{last}"
Interpolate into a double-quoted string
def <name>(a, b = 1, *rest, k:, **opts)
Define a method
if <a> ... elsif ... else ... end
Conditional
x = cond ? a : b
Ternary
<obj>&.<method>
Safe navigation: nil if obj is nil
x ||= <default>
Assign only if nil or false
case x when 1..5 then ... else ... end
Match with ===
3.times { |i| ... }
Repeat n times
:name %i[a b]Symbols and symbol array
{ a: 1, "b" => 2 }
Hash literals
->(x) { x + 1 }.call(2)
Lambda; also .(2) and [2]
&:upcasePass a method name as a block
yield / block_given?
Call the method's block
Strings & output
format("%05.1f %s", 3.14159, "x")
printf-style formatting
str.split(",")
Split into an array
str.gsub(/<re>/, "<new>")
Replace all matches
str.strip / chomp
Trim whitespace / trailing newline
Collections
arr.each { |x| ... }
Iterate
arr.map { |x| x * 2 }
Transform each element
arr.select { |x| x.even? }
Keep matches (reject inverts)
arr.reduce(0) { |sum, x| sum + x }
Fold into one value
arr.sort_by { |x| x.size }
Sort by a key
arr.group_by { |x| x.size }
Hash of key => elements
arr.each_with_index
Pairs of element and index
arr.each_with_object({}) { |x, h| ... }
Build a hash or array while iterating
arr.find { |x| ... }
First match or nil
arr.tallyCount occurrences
h.fetch(:k)Value or KeyError
h.fetch(:k, <default>)
Value or default
h.dig(:a, :b)Safe nested lookup
h.each { |k, v| ... }
Iterate pairs
h.transform_values { |v| ... }
Map values, keep keys
Pattern matching
case x in { name: String => n, age: } ... end
Match and bind a hash
case x in [a, *rest] ... end
Match an array and bind
in Integer | Float => n
Alternatives with binding the whole
<expr> => { name: }
Destructure, raise if no match
<expr> in { role: :admin }
Boolean match, no raise
Classes, Struct & Data
class <Name> ... end
Define a class
attr_reader :a / attr_accessor :a
Generate getters / getters+setters
def initialize(a) ; @a = a ; end
Constructor
class B < A ; super ; end
Inherit and call the parent
Point = Struct.new(:x, :y)
Mutable record with accessors
Point = Data.define(:x, :y)
Immutable value object
pt.with(x: 5)Copy with changes (Data)
Errors & requires
begin ... rescue Err => e ... ensure ... end
Handle errors
raise ArgumentError, "<msg>"
Raise an exception
rescue => eCatch StandardError in a def body
require "<lib>"
Load a library or gem
require_relative "<path>"
Load a file relative to this one
ARGV / ENV["<VAR>"]
Script args / environment
File.read("<f>") / File.readlines
Read a file / lines
Recipes
# values separated by spacesruby -lane 'BEGIN{s=0}; s += $F[1].to_f; END{puts s}' data.txtruby -i.bak -pe 'gsub(/foo/, "bar")' *.txtcurl -s <url> | ruby -rjson -e 'puts JSON.pretty_generate(JSON.parse($stdin.read))'ruby -run -e httpd . -p 8000
