stringio_irb

➜ irb
1.9.3p194 :001 > string = "This is a string"
 => "This is a string" 
1.9.3p194 :003 > require 'stringio'
 => true 
1.9.3p194 :004 > io = StringIO.new(string)
 => #<StringIO:0x007f988402a890> 
1.9.3p194 :005 > io.read(2)
 => "Th" 
1.9.3p194 :006 > string.slice!(2, -1)
 => nil 
1.9.3p194 :007 > io.read(2)
 => "is" 
1.9.3p194 :008 > string.slice!(2, -1)
 => nil 
1.9.3p194 :009 > io.read
 => " is a string"