Checking for STDIN in ruby

A colleague was asking today how he could see if there’s data waiting on STDIN in ruby (on Linux). On OS X, this is pretty straightforward:

if $stdin.stat.size > 0
  puts "got something: #{STDIN.read}"
else
  puts "nada"
end

That doesn’t work in Linux, though. After some digging, I found this post, which lead to:

require 'fcntl'

flags = STDIN.fcntl(Fcntl::F_GETFL, 0)
flags |= Fcntl::O_NONBLOCK
STDIN.fcntl(Fcntl::F_SETFL, flags)

begin
  puts "got something: #{STDIN.read}"
rescue Errno::EAGAIN
  puts "nada"
end

Which works on both platforms, but is (a) ugly (catching an exception), and (b) requires you to actually try to read from STDIN.

In playing around with that, though, I noticed that STDIN.fcntl(Fcntl::F_GETFL, 0) returned 0 if there was something on STDIN, and something non-zero (2 in OSX and 32770 in Linux) if STDIN was empty. So now the code is simple again:

require 'fcntl'

if STDIN.fcntl(Fcntl::F_GETFL, 0) == 0
  puts "got something: #{STDIN.read}"
else
  puts "nada"
end

I’m not sure how reliable that is on other platforms (it won’t work on Windows—fcntl is a Unix-y thing). If I’m understanding fcntl.h correctly, a return value of 2/32770 (0x8002) seems to indicate that the io stream in question is open for writing. I’m not sure if that is intended or just a side-effect. Anyone know?

Leopard External Monitor Annoyance Solved...aka Hide All Apps on a Mac

One of the more annoying things about Leopard is that when you plug in an external monitor that is set up to be your primary, your open applications don’t move over to the monitor. I was having to manually drag everything over. Then I realized that if I hid all my apps before plugging in the monitor, when I brought them up again, they’d be in the right place.

So now the question was: is there an easy way to hide all your apps without cycling through them all? It took a bit of digging, but it turns out there is. Cmd-option-click on an app in the Dock and it will hide all other apps. So I tried Cmd-option-click on the desktop itself and…voilà!

Update: Technically, you’re Cmd-option-clicking on the Finder, so if you have any Finder windows open, they won’t hide. Bummer.

ConditionsConstructor

I hadn’t posted this before because it seemed kind of trivial and silly, but I used it again the other day and decided maybe I should share the joy after all.

Far too often I find myself jumping through hoops building ActiveRecord find conditions arrays dynamically depending on what arguments were passed in to the method. So I cooked up a simple little class to clean that up a bit:

# class to construct conditions for AR queries

# cc = ConditionsConstructor.new('foobar > ?', 7)

# cc.add('blah is not null')

# cc.add('baz in (?)', [1,2,3])

# cc.conditions

# # => ["foobar > ? and blah is not null and baz in (?)", 7, [1, 2, 3]]

class ConditionsConstructor
  def initialize(str = nil, *args)
    @conditions_strs = str ? [str] : []
    @conditions_args = args
  end
  
  def add(str, *args)
    @conditions_strs << str
    @conditions_args += args
  end
  
  def conditions
    [@conditions_strs.join(' and ')] + @conditions_args
  end
end

Tracking the 123 Meme

I'm pretty late to the party, but I just ran across this on Chuck Hoffman's blog: "Grab the nearest book, open to page 123, go down to the 5th sentence, and type up the 3 following sentences."

Before I do that, I thought it would be interesting to try to track this meme back as far as possible. For the sake of my sanity, I'm not following multiple paths from posts that link to more than one source--I'll just pick the link that seems to be the primary source. So here goes:

nothing happens linked to Knowing and Doing linked to Exploration Through Example linked to a thaumaturgical compendium linked to michaelzimmer.org linked to Chronicles of Dissent linked to Fergie's Tech Blog linked to Threat Level linked to Danger Room linked to Abu Muqawama linked to Afganistanica: Mountain Tourism in Afghanistan linked to [My] State Failure Blog linked to Kings of War linked to MountainRunner linked to zenpundit.com linked to the glittering eye who gave a bad link that I had to track down to Independent Liberal linked to Donklephant linked to Stubborn Facts linked to another post on the same blog, linked to Sideways Mencken, who did not link, but referenced Internet Ronin linked to AmbivaBlog [and now I'm starting to tire of this game] linked to The Anchoress linked [not directly, had to dig it up *sigh*] to Some Have Hats linked to [again not directly...grr] Church of the Masses linked [incorrectly] to The Daily Grotto [warning! annoying chanting] linked to Aussie Coffee Shop linked to Where Angels Go which mentioned, but failed to link to the person who tagged them, so it's a dead end.

Whew. This was getting a bit tedious. Not to mention that it seemed to have gotten firmly entrenched in religious/pro-life blogs, which were getting on my nerves.

Just as well. Turns out Google returns almost half a million hits for "page 123" sentence, and there doesn't seem to be a way to sort results by date (the daterange operator failed me completely). The oldest post I could find on Google Blog search was this one, from November 24, 2004 (albeit for a slight variation on the meme--just the fifth sentence, not the three following it), but which clearly isn't the origin. Seems it was a meme floating around on LiveJournal around then. If anyone has better search-fu and can find an earlier post, let me know.

At this point, I've made myself pretty sick of this meme. Often it appears to be a means by which people can brag about whatever erudite text they may or may not actually be reading. Even so, I can't have wasted this much time and not play along. I've got two books nearly equidistant from my keyboard now. One is, at least in my field, too mundane to bother with: the Pickaxe book. The other sports the following 123/5/3 sentences:

The latissimus dorsi muscles have a major role in the deadlift: from the floor, the lat pulls back on the humerus to keep the arms from swinging forward away from the shins, and acts as an anchor on the upper part of the humerus to maintain the position of the bar directly under the shoulder blades until the bar crosses above the knees. The lats act in an essentially isometric way from the floor to the point where hip extension allows the arms to become vertical. At this point tension comes off the lats, and as the back becomes vertical, the arms drag the bar into the thighs as they assume an angle behind the vertical, opposite the starting position.

That's from Starting Strength by Rippetoe and Kilgore, which is a great book for learning how to do basic barbell lifts correctly (something we do a fair bit of in Crossfit). Coincidentally, that's just a couple pages past where I was actually reading about the deadlift. (Most interesting tidbit I've learned so far from the book: the importance of a solid grip when doing the dealift. If your hands start slipping, proprioceptive (love that word) feedback tells the back that what you're trying to lift is too heavy, and it basically gives up.)

I'm not going to inflict this on anyone else, but if you're reading this, feel free to prate on about whatever book you have near you.

Cheating for Fun

I recently checked out the Scramble application on Facebook, which is a knock-off of Boggle. It’s a fun diversion, even though I usually get my ass kicked. There’s an annoying chat window there, too, and invariably someone will accuse someone else of cheating, at which point a number of people will pipe up with “how would you cheat?”

This got me thinking…how would you cheat? You’d just have to write a Scramble puzzle solver that spit out all the words in on the board. That sounded like a fun problem. I hadn’t done anything with recursion in a while, so I gave it a go. Below is what I came up with. You’ll need a word list to run it. I originally used /usr/share/dict/words, but it was missing a lot of valid words (I think it only has base words, no plurals or tenses). So I stole the scrabble word list from the Debian scribble package, which worked much better.

Anyway, here you go:

• boggler.rb
• words.gz

I did try this out a couple times on Scramble and won handily. There’s really not much fun in that, though.

Note: This was really just an exercise in coming up with a fun algorithm, and is primarily intended for programmers. If you’re just looking to cheat at Boggle/Scramble, there are plenty of web sites that will help you with that, and with a lot less effort.