Getting Started with Narwhal, a Standard Library for JavaScript

I have been writing system administration scripts for a couple of years now, first with just regular Bash and later Python. In terms of bash scripting, I have to admit that while my invocations of my favorite tools, such as sed and find, have become more complicated my use of shell scripting programming statements has remained pretty basic. I don’t write shell scripts on a daily basis so in the weeks between writing scripts I manage to re-forget how to write a proper for loop and how to use getopts.

Sadly, this same applies to Python as I am no longer programming in Python on a regular basis. My old setup.py scripts are starting to look unfamiliar. Like a large and growing portion of web developers out there, I spend more than 90% of my time writing JavaScript and the other 10% a mix of PHP, Java, ruby, Python, etc. About 6 months ago I discovered the CommonJS project which seeks to create a standard library for JavaScript and Narwhal implementation of that developing library. There are many great uses of narwhal but my current favorite is the jake tool, which is clone of ruby’s popular rake tool. I have been using it for the repetitive tasks in the Karma project like generating documentation, cleaning up temporary files, and checking out the latest version and packaging it for deployment. I will cover Jake in my next tutorial.

“But JavaScript is a toy language!” you declare. “It isn’t meant for serious stuff like system administration.” Let me break it to you softly, by historical accident JavaScript may now be the most popular programming language and boasts some of the fastest run-times for a dynamic language. It isn’t any less-suited to utility scripting than its more august cousins Ruby and Python.

Setting up narwhal

Download and extract the http://github.com/280north/narwhal/zipball/master or http://github.com/280north/narwhal/tarball/master archive, or

$ git clone git://github.com/280north/narwhal.git

You should append the following text to your .bashrc file and then open a new terminal

export PATH=$PATH:~/narwhal/bin

Run “narwhal” or “js” (they are equivalent).

You need the java5 or java6 JDK to run narwhal which by default runs on top of Rhino, a JavaScript implemented on the Java JVM. Narwhal doesn’t play well with OpenJDK, so we need to get the JDK from sun. Below are instructions for getting Sun’s JDK and setting it up on Ubuntu Linux.

First add these lines to your /etc/apt/sources.list

deb http://us.archive.ubuntu.com/ubuntu/ jaunty multiverse
deb http://us.archive.ubuntu.com/ubuntu/ jaunty-updates multiverse

Then run

$ sudo aptitude update
$ sudo aptitude install sun-java6-jdk     # alternately, sun-java5-jdk

You may want to remove the extra lines from your sources.list after you have finished installing the package.

Next you may need to tell Ubuntu explicitly to use Sun’s JDK

$ sudo update-alternatives —config java

# There are at least 2 alternatives which provide `java’. 

Selection Alternative 

+ * 1 /usr/lib/jvm/java-6-openjdk/jre/bin/java 
2 /usr/lib/jvm/java-1.5.0-sun/jre/bin/java 

Press enter to keep the default[*], or type selection number:
# Choose #2

To test your install just run narwhal from the command line

you@computer:/$ narwhal
Rhino 1.7 release 3 PRERELEASE 2009 12 12
js> print("hello")
hello
js>

We can run our little “Hello World” as a script

// hello.js
print('hello world');


$ narwhal hello.js
hello


Narwhal has a number of command line options which you can list with narwhal --help

A Note on Narwhal Engines
Narwhal is a standard library for JavaScript, that can run on several different JavaScript implementations. So far it runs on top of Rhino, google’s V8, and Webkit’s JavaScriptCore. I believe that there are plans to run on top of the awesome node.js in the near future. You may find a Rhino a bit slow for your tastes but don’t let that put you off of Narwhal.

If you are using a Mac you can easily install the JavaScriptCore engine which is part of Webkit. It is approximately 10 times faster than rhino. I have not yet gotten it running successfully on linux. Narwhal has a package manager called tusk, which is comparable to ruby’s gem and Python’s easy_install.

$ tusk install narwhal-jsc
$ cd packages/narwhal-jsc
$ make
 # or "make webkit" if you want to use the jsc context from a webkit instance, 
# and thus have access to the DOM and other APIs
 

From here on, you can run narwhal-jsc by simply running “narwhal-jsc” or you can make it your default engine for narwhal by adding NARWHAL_ENGINE=jsc in your .bashrc or whatever file you use to control your bash shell settings.

That’s it for now, stay tuned for a tutorial on Jake, a rake clone. If you aren’t familiar with make or rake, they are excellent tools for automating repetitive administration tasks.