Fixing readline for the Ruby on Rails console

By -
Fixing readline for the Ruby on Rails console 
$ rails console
/home/user/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/irb/completion.rb:9:in `require': no such file to load -- readline (LoadError)
    from /home/user/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/irb/completion.rb:9:in `'
    from /home/user/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.9/lib/rails/commands/console.rb:3:in `require'
    from /home/user/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.9/lib/rails/commands/console.rb:3:in `'
    from /home/user/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.9/lib/rails/commands.rb:20:in `require'
    from /home/user/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.9/lib/rails/commands.rb:20:in `'
    from script/rails:6:in `require'
    from script/rails:6:in `
'
The problem is that Ruby is somehow not cofigured to load the readline library and thus cannot run its console. This is a downside of using a language specific package manager, seperate from your operating system's package manager.

First you need to install libreadline5 and libncurses5. I can't see why ncurses would be needed, but I am too lazy to uninstall it and check if it still works without the library. Using Apt on Ubuntu/Debian:

    $ sudoaptitudeinstall libreadline5-dev libncurses5-dev

Next you want to go configure and rebuild Ruby's readline extension. I am using RVM and so Ruby exists in ~/.rvm/src/ruby-1.9.2-p180/ for me. This can differ for you but running which ruby should tell you where yours is. 
cd ~/.rvm/src/ruby-1.9.2-p180/ext/readline
ruby extconf.rb
make
make install
Depending on your setup you might need to install it by running sudo make install instead. That is it! Now Ruby on Rails' console should load as intended.

Comments

Post a Comment

Popular posts from this blog

Inserting and Moving elements inside Ruby Array

By -
Here's is an array with 5 elements 2.1.2 :001 > arr = ["a", "b", "c", "d", "e"] => ["a", "b", "c", "d", "e"] Lets look at few different cases Insert a new element at starting position Using unshift 2.1.2 :002 > arr.unshift("f") => ["f", "a", "b", "c", "d", "e"] Using insert 2.1.2 :005 > arr.insert(0, "f") => ["f", "a", "b", "c", "d", "e"] In the above example 0 is the position(index) Move existing element from one position to another The element in this case is "e" Using uniq to show only unique elements 2.1.2 :009 > arr.insert(0, "e").uniq => ["e", "a", "b", "c", "d"] With uniq we are only showing unique records but the element is listed
Read more

Difference between Validations, Callbacks and Observers

By -
Validations allow you to ensure that only valid data is stored in your database. Example: validates_presence_of :user_name, :password validates_numericality_of :value We can write custom validation also as def validate   errors.add(:price, “should be a positive value”) if price.nil?|| price < 0.01 end Callbacks and observers allow you to trigger logic before or after an alteration of an object’s state. Callbacks are methods that get called at certain moments of an object’s life cycle. With callbacks it’s possible to write code that will run whenever an Active Record object is created, saved, updated, deleted, validated, or loaded from the database. Callbacks are hooks into the life cycle of an Active Record object that allow you to trigger logic before or after an alteration of the object state. This can be used to make sure that associated and dependent objects are deleted when destroy is called (by overwriting before_destroy) or to massage attribu
Read more