About a week ago, I advised Rogelio Gundino on Twitter that it was not only possible, but pretty fun to write command-line apps on OS X in Objective-C. I promised him that I’d make a blog post about it, and started drafting examples. The problem with sample code, of course, is that it’s sample code. There is a world of difference between:
- code written for an API presentation or tech demo
- code written to actually perform a useful task
Since I like to read (and write) the latter, I threw out three attempts at useful demonstration before I stumbled across Marco Arment’s clean-room implementation of the bcrypt cryptographic hash algorithm for PHP 5.3. Cryptography gets any developer nerd’s juices flowing, and I began to consider what it would take to port bcrypt to Objective-C.
It’s C All The Way Down
A nice side effect of Objective-C being a strict superset of ANSI C is that damn near any C code ever written is also Objective-C code that OS X and iOS developers can pick up and use without missing a beat (license restrictions notwithstanding, of course.) Instead of reinventing the bcrypt wheel, I was able to procure Ricardo Garcia’s public domain bcrypt C library from github to do the hard number crunching. This was a double-win: I didn’t have to reimplement a complex cryptographic algorithm by hand, and since it was written in C I was reasonably sure it would be more performant than anything I’d write myself.
Argumentative Parsing
When writing a command-line utility, you don’t have to worry about nibs, xibs, Interface Builder or writing AppKit/UIKit delegates. What you do have to concern yourself with is the proper parsing of command-line arguments. There are a ton of examples out there on how to do this in C. Since we’re working in Objective-C, however, I looked around for something that leveraged the language and environment. What I found was Dave Dribin’s ddcli command-line application framework. By writing a simple delegate object with the domain knowledge pertinent to your application’s arguments, you neatly avoid an unsightly main() function filled with if/else chains or long switch/case blocks while sticking with the creature comforts of Objective-C.
This Is Only A Test
I don’t really expect this project to go anywhere; I wrote it to see if I could pull it off and to provide compelling proof that Objective-C is not just for GUIs. That said, if you would like to grab the source and do something fun with it you can fork me on github.
Cheers, and happy coding!
