On Jul 13, 2011, at 14:51 , Simon Harrison wrote: > Thanks a lot. I didn't realise that FileUtils.mkdir accepted a format=20= > string. It doesn't. Philip's code is wrong. > 10000 % ruby > require 'fileutils' >=20 > (1..100).each do |num| > FileUtils.mkdir("prefix-%03d", num) > end > ^d > = /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/fi= leutils.rb:1436:in `dup': can't dup Fixnum (TypeError) > ... What you really want to execute is: > (1..100).each do |num| > FileUtils.mkdir "Prefix-%03d" % num > end which is just syntactic sugar for: > FileUtils.mkdir("Prefix-%03d".%(num))