Today this is pretty easy to do with Bundler. You make a local copy of the gem and then instead of doing

    gem &quot;whatever&quot;

in your Gemfile, you do:

    gem &quot;whatever&quot;, :path =&gt; &quot;/home/pupeno/whatever&quot;

After running bundle install, the gem is picked from that directory. Even if you modify something in there, all you need to do to re-load it is restart Rails.

If you need to deploy an application using your own changes of a Gem, you make a fork, on Github or similar and on the Gemfile you do:

    gem &quot;whatever&quot;, :git =&gt; &quot;git@github.com:/pupeno/whatever.git&quot;

and that&#39;s it. It&#39;s simple, straightforward and beautiful.

&gt; In all the cases the gems were at github so I would probably for it at github, clone it, make my chances and maintain my own branch. I suppose then I would install that branch directly with gem install on my server.

If you really need to hack the actual gem source then yes, that would be the way to do it. However, it should be a last resort. You don&#39;t want to maintain the actual gem if you don&#39;t have to. Why not extend classes from the gem source whose functionality you need to change and use your classes instead of the gem classes in your Rails code?

I find it rare that you actually need to hack 3rd party code directly to do what you need to do. Good software can be extended/easily augmented.

Is it possible to select multiple non-consecutive lines (or sections) in VIM&#39;s visual mode? If so, how?

Multiple selections in VIM

I am given a byte[] array in Java which contains the bytes for an image, and I need to output it into an image. How would I go about doing this?

Much thanks

Byte Array to Image object

I&#39;ve found myself twice in this situation: I install a gem on my system and start using it from my Rails project. Eventually I need to make some changes to that gem. How should I proceed?

Ideally I&#39;d like to check out the source code of that gem somewhere, like ~/third_party/gems, work on it and have my Rails project use that instead. Is that possible?

In all the cases the gems were at github so I would probably for it at github, clone it, make my chances and maintain my own branch. I suppose then I would install that branch directly with gem install on my server. Does that make sense?

Forking a gem for a Rails project

I've found myself twice in this situation: I install a gem on my system and start using it from my Rails project. Eventually I need to make some changes to that gem. How should I proceed?
Ideally I'd like to check out the source code of that gem somewhere, like ~/third_party/gems, work on it and have my Rails project use that instead. Is that possible?
In all the cases the gems were at github so I would probably for it at github, clone it, make my chances and maintain my own branch. I suppose then I would install that branch directly with gem install on my server. Does that make sense?

I&#39;d like to create a callback function in rails that executes after a model is saved.

I have this model, Claim that has a attribute &#39;status&#39; which changes depending on the state of the claim, possible values are pending, endorsed, approved, rejected

The database has &#39;state&#39; with the default value of &#39;pending&#39;.

I&#39;d like to perform certain tasks after the model is created on the first time or updated from one state to another, depending on which state it changes from.

My idea is to have a function in the model:

        after_save :check_state
    
        def check_state
          # if status changed from nil to pending (created)
          do this
        
          # if status changed from pending to approved
          performthistask
         end

My question is how do I check for the previous value before the change within the model?

How to detect attribute changes from model?

Is there a way to determine what version of Ruby is running from within Rails (either on the web or through `script/console`)? I have Ruby 1.8.6 installed but I&#39;ve also installed Ruby Enterprise Edition 1.8.7-20090928 and want to ensure that it&#39;s using the right installation.

Determine ruby version from within Rails

I just upgraded my rails to 2.3.4 and I noticed this with validations:
Lets say I have a simple model Company which has a name. nothing to it. 
I want to run my own validation:

    class Company &lt; ActiveRecord::Base
        
      validate :something
      
      
      def something
        false
      end
          
    end


saving the model actually works in this case.
The same thing happens if i override validate() and return false.
I noticed this in a more complex model where my validation was returning false, but the object was still saving...I tried it out in an essentially empty model and the same thing applied. Is there a new practice I am missing? This doesn&#39;t seem to be the case in some of my older rails code.



calling custom validation methods in Rails

I&#39;m looking at [this Railscast episode][1] and wondering why the call to `escape_javascript` is needed here:

    $(&quot;#reviews&quot;).append(&quot;&lt;%= escape_javascript(render(:partial =&gt; @review)) %&gt;&quot;);

What is `escape_javascript` used for?

According to [the Rails docs][2]:

&gt; escape_javascript(javascript)
&gt; 
&gt; Escape carrier returns and single and
&gt; double quotes for JavaScript segments.

But that doesn&#39;t mean much to me.


  [1]: http://railscasts.com/episodes/136-jquery
  [2]: http://api.rubyonrails.org/classes/ActionView/Helpers/JavaScriptHelper.html#M001758

Why escape_javascript before rendering a partial?

I&#39;m investigating a rails app - the prod server has two version of a specific gem installed, how can I tell which version the prod app is using?

How to tell which version of a gem a rails app is using

I am trying to decode some HTML entities, such as `&#39;&amp;amp;lt;&#39;` becoming `&#39;&lt;&#39;`.

I have an old gem ([html_helpers][1]) but it seems to have been abandoned twice.

Any recommendations? I will need to use it in a model.

[1]: http://github.com/tma/html_helpers/

How do I encode/decode HTML entities in Ruby?

Let&#39;s say I have a Ruby array

    a = [1, 2, 3, 4]

If I want all but the first item, I can write `a.drop(1)`, which is great. If I want all but the *last* item, though, I can only think of this way

    a[0..-2]   # or
    a[0...-1]

but neither of these seem as clean as using `drop`. Any other built-in ways I&#39;m missing?

All but last element of Ruby array

Is there a quick way to get every other entry in an Array in Ruby? Either the odd or even entries values with 0 included in the odd. I&#39;d like to be able to use it like this:

    array1 += array2.odd_values

or
    
    puts array2.odd_values.join(&quot;-&quot;)

for example

&lt;b&gt;Update&lt;/b&gt;

This give exactly what I&#39;m after but I&#39;m sure there is a shorter version.

    array1.each_with_index do |item,index| 
      if (index %2 ==0) then 
        array2.push(item) 
      end
    end

Odd (or even) entries in a Ruby Array

I&#39;ve missed the memo somewhere, and I hope you&#39;ll explain this to me.

Why is the eigenclass of an object different from `self.class`?

    class Foo
      def initialize(symbol)
        eigenclass = class &lt;&lt; self
          self
        end
        eigenclass.class_eval do
          attr_accessor symbol
        end
      end
    end

My train of logic that equates the eigenclass with `class.self` is rather simple:

`class &lt;&lt; self` is a way of declaring class methods, rather than instance methods. It&#39;s a shortcut to `def Foo.bar`.

So within the reference to the class object, returning `self` should be identical to `self.class`. This is because `class &lt;&lt; self` would set `self` to `Foo.class` for definition of class methods/attributes.

Am I just confused? Or, is this a sneaky trick of Ruby meta-programming?

Why isn&#39;t the eigenclass equivalent to self.class, when it looks so similar?

What are the differences between `fork` and `exec`?





Differences between fork and exec

What is the difference between `system` and `exec` family commands?  Especially I want to know which one of them creates child process to work?

Difference between &quot;system&quot; and &quot;exec&quot; in Linux?

I&#39;ve got a long running, daemonized Python process that uses subprocess to spawn new child processes when certain events occur. The long running process is started by a user with super user privileges. I need the child processes it spawns to run as a different user (e.g., &quot;nobody&quot;) while retaining the super user privileges for the parent process.

I&#39;m currently using

    su -m nobody -c &lt;program to execute as a child&gt;

but this seems heavyweight and doesn&#39;t die very cleanly.

Is there a way to accomplish this programmatically instead of using su? I&#39;m looking at the  os.set*uid methods, but the doc in the Python std lib is quite sparse in that area. 

Run child processes as different user from a long running Python process

Consider this code snippet:

    pid_t cpid = fork();

    if (cpid == -1) {
        perror(&quot;fork&quot;);
        exit(EXIT_FAILURE);
    }

    if (cpid == 0) { // in child
        execvp(argv[1], argv + 1);
        perror(&quot;execvp&quot;);
        _exit(EXIT_FAILURE);
    }

    // in parent

How shall I exit the child process if execvp returns? Shall I use exit() or _exit()?


how to exit a child process - _exit() vs. exit

Can anyone explain the difference between a fork and a thread?

What is the difference between fork and thread?

    qichunren@zhaobak:~&gt; gem install hpricot
    ERROR:  While executing gem ... (Gem::FilePermissionError)
        You don&#39;t have write permissions into the /opt/ruby-enterprise-1.8.7/lib/ruby/gems/1.8 directory.



Current login user is qichunren, and qichunre user have write permission with .gem dir.I would like to know why gem not install files into my home .gem dir first? Why my gem common first want to install files into /opt/ruby-enterprise-1.8.7/lib/ruby/gems/1.8

gem install permission problem

Specifically, the ruby-oci8 gem.  I have both 1.0.7 and 2.0.4 installed.  I want 1.0.7.

I can just require oci8, but I don&#39;t get the version I want.

    irb(main):001:0&gt; require &#39;oci8&#39;
    =&gt; true
    irb(main):002:0&gt; OCI8::VERSION
    =&gt; &quot;2.0.4&quot;

I can require using the full path to the file, which works, but is not going to be portable:

    irb(main):001:0&gt; require &#39;C:\Ruby\lib\ruby\gems\1.8\gems\ruby-oci8-1.0.7-x86-mswin32-60\lib\oci8&#39;
    =&gt; true
    irb(main):002:0&gt; OCI8::VERSION
    =&gt; &quot;1.0.7&quot;

I can use the gem command to ask for the version I want, but it doesn&#39;t appear to actually load the library:

    irb(main):001:0&gt; gem &#39;ruby-oci8&#39;, :lib=&gt;&#39;oci8&#39;, :version=&gt;&#39;=1.0.7&#39;
    =&gt; true
    irb(main):002:0&gt; OCI8::VERSION
    NameError: uninitialized constant OCI8
        from (irb):2

I would definitely favor this last approach if would load the library, rather than just confirming that it&#39;s present on my system.  What am I missing?

How do I require a specific version of a ruby gem?

Linux newbie question I guess..

How can I find out where gem installs the gems on my Ubuntu 10 system? I want to read gem sourcecode and perhaps change things up a bit.



Where are my ruby gems?

I&#39;m certainly no Ruby developer but I have an application on my server using Ruby, Gems, and Bundler. I am trying to install another Ruby on under a different user account but on the same VPS. When I go to run 

    bundle install

I get the following error:

&gt; Could not locate Gemfile

I could remove the contents of the ./bundle directory so that all Gems are re-fetched to clear the error but will this have an impact on my other application using the same Gems and Bundler? I don&#39;t want to risk taking the other app down.



Could not locate Gemfile

I&#39;m doing an engine here, it works alright in stand alone.

When I transform it into a gem, and load it inside another application, I get a lot of undefined errors, coming from my engine gem&#39;s dependecies.

Here is the gemspec:


    s.add_dependency(&#39;paperclip&#39;)
    s.add_dependency(&#39;jquery-rails&#39;)
    s.add_dependency(&#39;rails3-jquery-autocomplete&#39;)
    s.add_dependency(&#39;remotipart&#39;)
    s.add_dependency(&#39;cancan&#39;)

In the application, when I do a bundle install, it lists all these dependencies, but as i run the application I receive a lot of undefined methods errors (has_attachment from paperclip for example). It seems that the application doesn&#39;t load the engines dependencies.
Is this the default behavior? Can I change it?
Same thing happened with a plugin inside the engine.

If I insert by hand those gems, in the application Gemfile, all works...





Content Type	Original Author	Original Content on Stackoverflow
Question	pupeno	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	pupeno	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	Chris	View Answer on Stackoverflow

Forking a gem for a Rails project

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Byte Array to Image object

Multiple selections in VIM

Attributions