npm cache directory

# 02 Feb 2015

To keep npm from writing to your home directory, override the cache location.

export NPM_CONFIG_CACHE="./.npm"
npm install

Or, put an .npmrc in your package’s root directory.


Scala, recursive retry

# 31 Mar 2014

Deploy Jekyll with Rake and rsync

# 18 Feb 2014

Check For Positive Integer Overflow in Java

# 10 Feb 2014

Dreamhost: failed to import extension hgext.imerge: No module named imerge

# 08 Apr 2011

Edit your .hgrc file:

hgext.imerge = !

via pixelastic

Changing user httpd DocumentRoot in OS X

# 16 Mar 2011

While testing a locally running web application in OS X 10.6.6, I discovered that DocumentRoot appears to be set incorrectly. I wasn’t able to refer to a file like /Users/username/Sites/style.css as /style.css in the web app source.

If you have Web Sharing turned on, each user’s httpd DocumentRoot is not automatically set to /Users/username/Sites, as I expected.

But each user does have there own personal httpd.conf file in /private/etc/apache2/users.

Find yours, then add the following, replacing username with your own:

DocumentRoot /Users/username/Sites

Toggle Web Sharing off/on, and it should be fixed.

Deploying non-rails apps with Capistrano, Mercurial, and Bitbucket

# 14 Mar 2011

Capistrano makes deploying Ruby on Rails applications easy. Having experienced how easy, I was eager to use Capistrano to make deploying non-Rails applications just as easy. I wasn’t able to find comprehensive info on actually making this work from start to finish. Here’s how to do it.


Your version control system of choice is Mercurial, stored at Bitbucket. You want to deploy to a server running Apache. Your development machine is running Mac OS X and you have Capistrano installed.

Capifying Your Project

Capistrano has fairly good documentation for this step, and I don’t see this changing much in the future. Open and run:

cd /path/to/your/project
mkdir config
capify .

Capistrano will create a couple of files for you. The important one is config/deploy.rb. Open it. Then replace its contents with the following:

# User for deployment server
set :user, "your server user here"
set :use_sudo, false # don''t try to use root access

set :application, "your application name here"

# short form instead of the role-based definitions just below
server "your server url here", :app, :web, :db, :primary => true

role :web, "your web-server here"                          # Your HTTP server, Apache/etc
role :app, "your app-server here"                          # This may be the same as your `Web` server
role :db,  "your primary db-server here", :primary => true # This is where Rails migrations will run
# role :db,  "your slave db-server here"

# Deployment will actually be to #{deploy_to}/current, so your document root on your server needs to be set to that also.
set :deploy_to, "/path/to/www/directory"

set :repository,  "ssh://"

set :scm, :mercurial
# Or: `accurev`, `bzr`, `cvs`, `darcs`, `git`, `mercurial`, `perforce`, `subversion` or `none`


# Overriding some tasks in the ''deploy'' namespace since this isn''t a rails app. This way, you can still use ''cap deploy'' to deploy this app.
namespace :deploy do
  task :start do ; end
  task :stop do ; end
  task :restart do
    run "ln -nfs #{release_path} #{current_path}"
# Or, use this as a backup if overriding the deploy tasks above does not work for some reason. Then, deploy with ''cap deploy_nonrails''.
# task :deploy_nonrails, :roles => :app do
#  run "hg clone #{repository} #{release_path}"
#  run "ln -nfs #{release_path} #{current_path}"
#  run "ln -nfs #{shared_path}/uploaded #{current_path}/uploaded"
# end

Now, update deploy.rb with your specific information. You have been Capify’d!

Bitbucket Authentication

You will notice that in deploy.rb, we have only told Capistrano about Bitbucket via the repository parameter, and that we are using a URL that begins with SSH. This means that authentication with the Bitbucket server will be via SSH, which will require that we have a public-private key pair. We will set that up now.

Bitbucket has a helpful page which covers how to access your Bitbucket repository via SSH. The important part of it for this discussion is to set up your public key with Bitbucket.

If you don’t have a public-private key pair, follow that guide to set one up. In, run:


And follow the prompts. Make sure to note the location of your public key so that you can get to it later. It is probably at ~/.ssh/ or ~/.ssh/

Now, you’ll need to give Bitbucket your public key (ends in .pub). Look in your Bitbucket Accounts page to find where to do that.

Also, update your local repository’s parent by updating .hg/hgrc in your repository’s root with:

default = ssh://

You should be able to connect to Bitbucket without typing a password.

Deployment Server Setup

Just copy your public key into ~/.ssh/authorized_keys on your deployment server. Assuming that you don’t already have any public keys set up already then run:

scp ~/.ssh/ user@server:~/.ssh/authorized_keys

You should now be able to authenticate with your server without typing a password.

You’ll also want to change your Apache HTTPD document root to point to the current alias that Capistrano will create in your server’s www root. Different web hosts have different ways of allowing you to do this. Mine provides a web interface that can adjust this setting. Check yours.

SSH Key Forwarding

This was, for me, the trickiest part. What Capistrano is going to do when you deploy your application is connect to your deployment server (authenticating using your private key on your development machine and your public key in ~/.ssh/authorized_keys on your deployment server), and then, from your deployment server, connect to your Bitbucket server to access your repository.

In order for this to work, SSH Agent Forwarding must be enabled on your development machine. Add this to ~/.ssh/config, creating the file if it doesn’t already exist:

Host *
ForwardAgent yes

Running Capistrano

Open up, navigate to your project’s root directory, and run:

cap deploy

The most recent version of your application in Bitbucket should now be deployed to your server.

Push from Mercurial to ClearCase

# 20 Jun 2010

I sometimes like do my development work in a local Mercurial repo even though I’m stuck checking into ClearCase in the end.

I create a fresh snapshot view in ClearCase, create a Mercurial repo on the view, then do my work in a clone of that Mercurial repo. It isn’t ideal, but it allows me to delay all the file checkin/checkout work required when dealing with ClearCase. The main advantage is that it frees me to use whatever IDE or text editor I want, without relying on an integrated ClearCase plugin.

The tricky part comes when it is time to push my changes from my clone to the hybrid Mercurial/ClearCase repository/snapshot view — or more accurately, after the push, during a hg update on the hybrid repo/view.

I’ve been using this bash script (run in Cygwin since ClearCase isn’t available for OS X) to help with that step.

#!/bin/env bash

while [ 1 ]; do
  file=`hg up 2>&1 1>/dev/null | grep abort | grep "Access is denied" | awk -F" " ''{print $2}'' | awk -F":" ''{print $1":"$2}''`
  if [ "$file" == "" ]; then
    echo "No pending updates."
    exit 1
  echo "$file"
  cleartool co -nc $file

It continuously attempts to update (via hg update) the hybrid repo/view, and looks for files that need to be Checked Out in the ClearCase snapshot, and then checks them out.

Lazy initialization in Ruby using lambda

# 05 May 2010

If you want to use lazy initialization in Ruby the ||= trick is an easy and readable way to do it.

class Tree
  def estimated_yield
    @estimated_yield ||= get_estimated_yield
  def get_estimated_yield
    n = 0
    branches.each { |branch| n += branch.fruits + branch.berries }

Rather than bury the actual “get fruit” logic inside of another function though, I’ve found it handy to use a Proc if that logic doesn’t need to be re-used elsewhere.

class Tree
  def estimated_yield
    @estimated_yield ||= lambda {
      n = 0
      branches.each { |branch| n += branch.fruits + branch.berries }