Apple provides a class that we can use for this to great effect: NSCharacterSet. We want alphanumeric characters, so we can create a character set of the characters we want using this method:

NSCharacterSet *alphanumericSet = [ NSCharacterSet alphanumericCharacterSet ];

Now we have a character set like we want. We just need a way to turn our string into a string that contains only those characters. Unfortunately, the closest thing in NSString’s implementation is the -stringByTrimmingCharactersInSet: method. But that seems to do the opposite of what we want. Fortunately NSCharacterSet has our back here. We can use the -invertedSet method. So here is our final code:

NSString *beginningString = @"Some string with non-alphanumeric characters. !@#$%^&*()";
NSCharacterSet *nonalphanumericSet = [[ NSCharacterSet alphanumericCharacterSet ] invertedSet ];
NSString *endingString = [ beginningString stringByTrimmingCharactersInSet:nonalphanumericSet ];

In this example, endingString will be equal to “Somestringwithnonalphanumericcharacters”.

UPDATE: As it turns out, this only works if the non-alphanumeric characters are at the beginning or end of the NSString. Whoops.

tell application "Finder"
	set screen_resolution to bounds of window of desktop
	set screen_width to item 3 of screen_resolution
	set screen_height to item 4 of screen_resolution
end tell

tell application "System Events" to tell process "Dock"
	set dock_dimensions to size in list 1
	set dock_height to item 2 of dock_dimensions
end tell

set desired_width to 1400

set side_space to screen_width - desired_width
set left_bound to (side_space / 2)
set right_bound to left_bound + desired_width
set bottom_bound to screen_height - dock_height
set top_bound to 22 (* for the menu bar *)

try
	tell application "iTunes"
		activate
		set the bounds of the first window to {left_bound, top_bound, right_bound, bottom_bound}
	end tell
end try

try
	tell application "Firefox"
		activate
		set the bounds of the first window to {left_bound, top_bound, right_bound, bottom_bound}
	end tell
end try

try
	tell application "Mail"
		activate
		set the bounds of the first window to {left_bound, top_bound, right_bound, bottom_bound}
	end tell
end try

try
	tell application "Vienna"
		activate
		set the bounds of the first window to {left_bound, top_bound, right_bound, bottom_bound}
	end tell
end try

With that in place, I saved it as an application in ~/Applications, and put it in my Dock. Now, whenever I change resolutions, I just click the button and everything is how I like it.

To change the script, you should be able to add any application with an AppleScript dictionary that supports moving and sizing the window.  The numbers I’ve used make the windows 1,400px wide, and the height that you want will depend on the size of your Dock. The script moves windows to the center, desired_width wide, and from the menubar to the Dock.

Note: I have had some trouble recently; sometimes when I change my resolution the AppleScript doesn’t pick it up.  To combat this, I told the Displays System Preferences pane to keep its icon in the menu bar; when my script uses the incorrect resolution, I change my screen resolution then change it back, which is enough for the script to detect the change.

Update 2008-05-28: Made some usability changes. Details here.