Files and IO

Question 1

What is the standard subclass of IO?

Answer 1

File class

Question 2

What are the Socket library subclasses from IO?

Answer 2

TCPSocket or UDPSocket

Question 3

Which extension provides methods for interacting with the console?

Answer 3

The io/console extension provides methods for interacting with the console. The console can be accessed from IO.console

Question 4

Name some IO console methods?

Answer 4

io/console have the following methods:

IO::console
IO#raw,IO#raw!
IO#cooked,IO#cooked!
IO#getch
IO#echo=,IO#echo?
IO#noecho
IO#winsize,IO#winsize=
IO#iflush
IO#ioflush
IO#oflush
Example
require 'io/console'
rows, columns = $stdout.winsize
puts "Your screen is #{columns} wide and #{rows} tall"

Question 5

How can you open the file using File class?

Answer 5

There are two methods to open a file in Ruby:

File.new method : Using this method a new file can be created for reading, writing or both.
File.open method : Using this method a new file object is created. That file object is assigned to a file.

Difference between both the methods is that File.open method can be associated with a block while File.new method can’t.

Syntax:

f = File.new(“fileName.rb”)

Or,

File.open(“fileName.rb”, “mode”) do |f|

Question 6

What are the ways to read a file using File class?

Answer 6

There are three different methods to read a file.

To return a single line, following syntax is used.

Syntax: f.gets
code…
To return the whole file after the current position, following syntax is used.

Syntax: f.read
code…
To return file as an array of lines, following syntax is used.

Syntax: f.readlines
[code…]

Question 7

Explain sysread method?

Answer 7

The sysread method is also used to read the content of a file. With the help of this method you can open a file in any mode.

aFile = File.new("about.txt", "r")   
if aFile   
   content = aFile.sysread(40)   
   puts content   
end

Question 8

Explain syswrite method?

Answer 8

With the help of syswrite method, you can write content into a file. File needs to be opened in write mode for this method.

aFile = File.new(“about.txt”, “r+”)
if aFile
aFile.syswrite(“New content is written in this file.\n”)
end

Question 9

What are the following open mode implies?

w+
r+
a+

Answer 9

“w+” Read-write, truncates existing file to zero length
or creates a new file for reading and writing.

“r+” Read-write, starts at beginning of file.

“a+” Read-write, each write call appends data at end of file.
Creates a new file for reading and writing if file does
not exist.

Question 10

Explain STDIN,STDOUT,STDERR?

Answer 10

Ruby IO objects wrap Input/Output streams. The constants STDIN, STDOUT, and STDERR point to IO objects wrapping the standard streams. By default the global variables
$stdin,

$stdout, and

$stderr point to their respective constants.

$stdin is read-only while $stdout and $stderr are write-only.