require 'stringio'
s = StringIO.new %{I am the very model of a modern major general.
I've information vegetable, animal, and mineral.}
s.pos

s.each_line { |x| puts x }

I am the very model of a modern major general.
I've information vegetable, animal, and mineral.

I am the very model of a modern major general.
I've information vegetable, animal, and mineral.

s.eof?

s.pos

s.rewind
s.pos

s.grep /general/

s = StringIO.new
s.write('Treat it like a file.')
s.rewind
s.write("Act like it's")
s.string

require 'yaml'
s = StringIO.new
YAML.dump(['A list of', 3, :items], s)
puts s.string

---
- A list of
- 3
- :items

--- 
- A list of
- 3
- :items

def make_more_interesting(io)
  io << "... OF DOOM!"
end
make_more_interesting("Cherry pie")

open('interesting_things', 'w') do |f|
  f.write("Nightstand")
  make_more_interesting(f)
end
open('interesting_things') { |f| f.read }

poem = %{The boy stood on the burning deck
Whence all but he had fled
He'd stayed above to wash his neck
Before he went to bed}
output = open("poem", "w")
output.write(poem)
output.close
input = open("poem")
poem.grep /ed$/

input.grep /ed$/

input.grep /ed$/

input.rewind
input.grep /ed$/

def fifth_byte(file)
  file.seek(5)
  file.read(1)
end
fifth_byte("123456")

NoMethodError: undefined method `seek' for "123456":String
...

NoMethodError: undefined method `seek' for "123456":String
	from (irb):43:in `fifth_byte'
	from (irb):46

fifth_byte(StringIO.new("123456"))

def file_operation(io)
  io = StringIO(io) if io.respond_to? :to_str && !io.is_a? StringIO
  #Do the file operation...
end
s = StringIO.new
s << "A string"
s.read
s << ", and more."
s.rewind
s.read