Deleting from Chrome’s History

Posted on 2011-11-08 by Ben Atkin

I wrote a script to delete URLs containing a string from Chrome’s history. It works for me. I don’t understand everything that it does, though, so it may have serious flaws. Use at your own risk.

# Removing history entries from Chrome that contain a search phrase
# Exit out of Chrome first
# Back up files and do this at your own risk

# gem install sqlite3 && gem install sequel

require 'sequel'

search_string = 'reddit'

# Delete history cache files
path = File.expand_path('~/Library/Application Support/Google/Chrome/Default')
cache_dirs = Dir.entries(path).select {|dir| dir != 'History' && dir.index('History') == 0}.map {|dir| File.join path, dir}
cache_dirs.each {|dir| File.delete dir}

# Delete matching history from sqlite3
DB = Sequel.sqlite File.join(path, 'History')
matching_urls = DB[:urls].filter(:url.like("%#{search_string}%"))
puts %Q[Deleting #{matching_urls.count} urls matching "#{search_string}"]
matching_urls.delete

I really like sqlite and Sequel.

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A JSON Column Coder for Rails 3.1

Posted on 2011-11-07 by Ben Atkin

Rails 3.1 has a serialize function that can take a custom column coder. A custom coder needs to have dump and load methods set, or else it will be recognized as a required type for the built-in YAML coder called YAMLColumn.

While the JSON class has the two required methods, it doesn’t allow specifying a default. So I created a custom coder. I don’t know where the best file and module locations to put the class in are, so I won’t include them here. This is the class, though:

class JSONColumn
  def initialize(default={})
    @default = default
  end

  # this might be the database default and we should plan for empty strings or nils
  def load(s)
    s.present? ? JSON.load(s) : @default.clone
  end

  # this should only be nil or an object that serializes to JSON (like a hash or array)
  def dump(o)
    JSON.dump(o || @default)
  end
end

Since load and dump are instance methods, an instance of JSONColumn needs to be passed rather than the class. Here’s an example that works for me inside of the rails console:

class Person < ActiveRecord::Base
  validate :name, :pets, :presence => true
  serialize :pets, JSONColumn.new([])
end

Update: Added .clone to the load method. HT @miyagawa.

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converting a search to a replace in vim

Posted on 2011-11-05 by Ben Atkin

I just googled something I’ve always wanted to know how to do in vim, and was surprised how quickly I found the answer.

In vim, there are separate modes for searching and commands. This generally works well as they have separate completion buffers and since I do them a lot, it keeps my command history from cluttering up my search history and vice versa. The area where I’ve wished that they were unified is when I want to convert from a search to a substitution expression. Normally in vim you do search expressions in search mode and command expressions in command mode. For example, if I wanted to search for trailing whitespace I might type:

/\s\s*

If I want to replace it with an empty string through the whole file I might type:

:%s/\s\s*//g

I can’t remove the / at the front of the command line with a backspace and replace it with a colon, so until I learned the tip I’m about to reveal I had to retype it. No longer.

The StackOverflow answer I found for the query, Convert vim / search to search and replace without retyping regular expression, suggests this remarkably simple technique:

You can type

/search_term

and then

:%s/<ctrl-r>// etc

where you actually press ctrl+r and then / to insert the search term.

It works! No longer do I desire for search and command modes to be unified.

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Simple Outline XML and Slim

Posted on 2011-11-05 by Ben Atkin

There’s nothing new about expressing XML in a significant-indentation format. Here’s Slim next to one from 2001.

Simple Outline XML (2001)

html>
    head>
        title> My Home Page
    body>
        h1> Contact Details
        p>  I can be contacted at
            a>  href=mailto:me@myplace.net
                this address
            except when on vacation.

Wikipedia Article

Slim (2010)

html
  head
    title My Home Page
  body
    h1 Contact Details
    p I can be contacted at
      a href="mailto:me@myplace.net" this address
      except when on vacation.

They’re quite similar. I find Slim a bit more comfortable in a ruby environment because it’s a bit more terse and uses two spaces like Ruby code does. It also is a templating language too. (In fact, I’m not sure there are converters going in both directions between XML/HTML and non-templated Slim. It could make a nice addition.)

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vim’s lcd command

Posted on 2011-11-04 by Ben Atkin

I find vim’s :lcd command to be quite useful. For a long time I didn’t use it, mainly because I didn’t understand how it works.

First, using it is simple. It works just like :cd. You type :lcd path/to/directory in command mode. The path is relative to the current directory, so :lcd .., :lcd ~/Desktop, and :lcd /etc/apache2 all work.

The :lcd command changes the path of the current window. The current window is the current frame within the current tab. Now, what’s really neat, is that a new window (created from commands such as :sp and :tabedit) gets the local directory of the window it’s created from.

Most plugins respect it. Both Command-T and ack.vim search within the local current directory. Another plugin, fugitive, bases its commands on the git repository of the current file so it works smoothly with different local directories as well.

Bang commands (like :!cp README.md ~/Desktop) also use the local current directory.

Finally, after using it for a while it gets easy to tell which directory I’m in. The status line displays the path of the current file based on the local current directory, so if I know where the current file is I can quickly figure out where the local current directory is.

I used it the other day with bundle show to dig through the source of two dependencies of my Rails project to better understand them.

If you use vim and haven’t got in the habit of using :lcd I highly recommend it. If you use another editor and wish it handled working in multiple directories gracefully, consider giving vim a shot!

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