Fun with CoffeeScript

Now that I can edit CoffeeScript files, what can I do with them? Well, I can run them just by adding a shebang line with coffee on it

#!/usr/bin/env coffee

console.log "Hello, World!"

If I put that in a file called hello.coffee, then I can run it with

$ ./hello.coffee 
Hello, World!

and get just what you think. How about if we define a hello function and call it with whatever is passed in on the command line?

#!/usr/bin/env coffee

hello = (name = "World") -> "Hello, #{name}!"

console.log hello(process.argv[2])

If I call it with a name, I get a personal greeting. Otherwise, I get the generic greeting.

$ ./helloyou.coffee oylenshpeegul
Hello, oylenshpeegul!

$ ./helloyou.coffee
Hello, World!

We would probably write this in Perl as

#!/usr/bin/env perl

use v5.14;
use warnings;

my $name = shift // 'World';

say "Hello, $name!";

but it's really more analogous to

#!/usr/bin/env perl

use v5.14;
use warnings;

sub hello {
    my $name = shift // 'World';
    return "Hello, $name!";
}

say hello($ARGV[0]);

We are calling the hello subroutine with an element from the argument list which may not be there. CoffeeScript's normal behavior for subroutine arguments is like Perl's "defined or" (//). We can see this if we look at the JavaScript for it.

$ coffee -c helloyou.coffee
$ cat helloyou.js 
(function() {
  var hello;
  hello = function(name) {
    if (name == null) {
      name = "World";
    }
    return "Hello, " + name + "!";
  };
  console.log(hello(process.argv[2]));
}).call(this);

Note that we're using argv[2]. This is apparently a Node thing; argv[0] is the interpreter (coffee), argv[1] is us (./helloyou.coffee), so our argument list starts with argv[2].

Speaking of Node, let's use its http module to try our hand at retrieving a Futurama quote from Slashdot.

#!/usr/bin/env coffee

http = require 'http'

ucfirst = (str) ->
    str.substr(0, 1).toUpperCase() + str.substr(1)

http.get host: 'slashdot.org', (res) ->
    for c in ['fry', 'bender']
        k = "x-#{c}"
        if res.headers[k]
            console.log "#{ucfirst(c)}: #{res.headers[k]}"

I'm doing a GET here (Is this a waste? I don't know how to do a HEAD.) and then looking for the Fry and Bender response headers, just as we did in dotperl. I don't have a ucfirst in CoffeeScript, so I wrote one using JavaScript's toUpperCase method.

$ ./futurama.coffee
Fry: Where's Captain Bender? Off catastrophizing some other planet?

Keen! I'm really enjoying CoffeeScript!