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What’s the difference between a string and a symbol in Ruby?

The main difference is that multiple symbols representing a single value are identical whereas this is not true with strings. For example: irb(main):007:0> :test.object_id => 83618 irb(main):008:0> :test.object_id => 83618 irb(main):009:0> :test.object_id => 83618 Those are three references to the symbol :test, which are all the same object. irb(main):010:0> “test”.object_id => -605770378 irb(main):011:0> “test”.object_id => … Read more

Issue updating Ruby on Mac with Xcode 4.3.1

Short answer is you can grab RVM master branch (not stable) to build it with LLVM (not gcc, I mistyped initially). It has appropriate patches to make 1.9.3-p125 to run (at least better) with Xcode 4.3.1 by default. I provided the patch. If you already installed RVM, rvm get head will install the master branch. … Read more

How to check if a URL is valid

Notice: As pointed by @CGuess, there’s a bug with this issue and it’s been documented for over 9 years now that validation is not the purpose of this regular expression (see https://bugs.ruby-lang.org/issues/6520). Use the URI module distributed with Ruby: require ‘uri’ if url =~ URI::regexp # Correct URL end Like Alexander Günther said in the … Read more

Create two-dimensional arrays and access sub-arrays in Ruby

There are some problems with 2 dimensional Arrays the way you implement them. a= [[1,2],[3,4]] a[0][2]= 5 # works a[2][0]= 6 # error Hash as Array I prefer to use Hashes for multi dimensional Arrays a= Hash.new a[[1,2]]= 23 a[[5,6]]= 42 This has the advantage, that you don’t have to manually create columns or rows. … Read more

How do I run a rake task from Capistrano?

A little bit more explicit, in your \config\deploy.rb, add outside any task or namespace: namespace :rake do desc “Run a task on a remote server.” # run like: cap staging rake:invoke task=a_certain_task task :invoke do run(“cd #{deploy_to}/current; /usr/bin/env rake #{ENV[‘task’]} RAILS_ENV=#{rails_env}”) end end Then, from /rails_root/, you can run: cap staging rake:invoke task=rebuild_table_abc

How can I have ruby logger log output to stdout as well as file?

You can write a pseudo IO class that will write to multiple IO objects. Something like: class MultiIO def initialize(*targets) @targets = targets end def write(*args) @targets.each {|t| t.write(*args)} end def close @targets.each(&:close) end end Then set that as your log file: log_file = File.open(“log/debug.log”, “a”) Logger.new MultiIO.new(STDOUT, log_file) Every time Logger calls puts on … Read more

Adding a directory to $LOAD_PATH (Ruby)

The Ruby load path is very commonly seen written as $: , but just because it is short, does not make it better. If you prefer clarity to cleverness, or if brevity for its own sake makes you itchy, you needn’t do it just because everyone else is. Say hello to … $LOAD_PATH … and … Read more

Why isn’t the eigenclass equivalent to self.class, when it looks so similar?

class << self is more than just a way of declaring class methods (though it can be used that way). Probably you’ve seen some usage like: class Foo class << self def a print “I could also have been defined as def Foo.a.” end end end This works, and is equivalent to def Foo.a, but … Read more

What does send() do in Ruby?

send sends a message to an object instance and its ancestors in class hierarchy until some method reacts (because its name matches the first argument). Practically speaking, those lines are equivalent: 1.send ‘+’, 2 1.+(2) 1 + 2 Note that send bypasses visibility checks, so that you can call private methods, too (useful for unit … Read more

How to create a file in Ruby

Use: File.open(“out.txt”, [your-option-string]) {|f| f.write(“write your stuff here”) } where your options are: r – Read only. The file must exist. w – Create an empty file for writing. a – Append to a file.The file is created if it does not exist. r+ – Open a file for update both reading and writing. The … Read more