My one-line solution.
Just join the below 4 lines become one single line; even no need space
when join lines.

require'open-uri';puts (ARGV.size !=1)?"Usage: #$0 <zip code>":
("The temperature in #$1 is #$2 degrees F."if
%r|Weather</b> for <b>(.*?)</b>.*?(\d+)&deg;F|=~
open("http://www.google.com/search?hl=en&q=temperature+#{ARGV[0]}"){|f|f.read})