This page contains automated test results for code from O'Reilly's Ruby Cookbook. If this code looks interesting or useful, you might want to buy the whole book.

Truncating a File
CodeExpectedActual
filename = 'truncate.txt'
open(filename, 'w') { |f| f << "All of this will be truncated." }
File.size(filename)
 30 30 
f = open(filename, 'w') {}
File.size(filename)
 0 0 
open(filename, 'w') { |f| f << "Here are some new contents." }
File.size(filename)
 27 27 
f = open(filename, File::TRUNC) {}
File.size(filename)
 0 0 
open(filename, File::TRUNC) do |f| 
  f << "At last, an empty file to write to!"
end
 
IOError: not opened for writing
...
 
IOError: not opened for writing
	from (irb):11:in `write'
	from (irb):11
	from (irb):10

f = open(filename, 'w') do |f|
  f << 'These words will remain intact after the file is truncated.'
end
File.size(filename)
 59 59 
File.truncate(filename, 30)
File.size(filename)
 30 30 
open(filename) { |f| f.read }
 "These words will remain intact" "These words will remain intact" 
f = open(filename, "w") { |f| f << "Brevity is the soul of wit." }
File.size(filename)
 27 27 
File.truncate(filename, 30)
File.size(filename)
 30 30 
open(filename) { |f| f.read }
 "Brevity is the soul of wit.\000\000\000" "Brevity is the soul of wit.\000\000\000"