[temp] Pages 120-1: Opening and closing files, Reading and writing files

Value: Medium

Level: Easy

Summary:
You can create a File object and read from it, write to it, or both. You can do it using File#new() or File#open(): the only difference between the two is that the latter can be associated with a block. If you use File#open() with an associated block Ruby will pass the file as a parameter to the block, and at the end will close the file. In case of exception Ruby will nevertheless close the file before raising it: if there's no block associated, or if you're using File#new(), you'll have to ensure to close the file as Ruby won't do it automatically.


Memo: Be sure your file will be closed even if an exception is raised.

Example:

Assuming we have data in data.txt we can read it in a standard way...

print File.new("data.txt", "r").readlines
# produces the same otuput of...
print File.open("data.txt", "r").readlines

... or in a "safe" way

File.open("data.txt", "r") do |a|
print a.readlines
end
# produces the same output of...
File.open("data.txt", "r") do |b|
while line = b.gets
print line
end

Finally we could have show.rb...

while line = gets
puts line
end

...and simply pass it one or more filenames in the command line

% ruby show.rb data.txt

Doubts: 0

Reported errata (at 10/17/06 14:17:18 PDT): 0

Errata I found: 1

• Typo on page 121: "w" instead of "we".
  

My suggestions to the author: 0