Ruby LanguageFile and I/O Operations

Parameters

FlagMeaning
"r"Read-only, starts at beginning of file (default mode).
"r+"Read-write, starts at beginning of file.
"w"Write-only, truncates existing file to zero length or creates a new file for writing.
"w+"Read-write, truncates existing file to zero length or creates a new file for reading and writing.
"a"Write-only, starts at end of file if file exists, otherwise creates a new file for writing.
"a+"Read-write, starts at end of file if file exists, otherwise creates a new file for reading and writing.
"b"Binary file mode. Suppresses EOL <-> CRLF conversion on Windows. And sets external encoding to ASCII-8BIT unless explicitly specified. (This flag may only appear in conjunction with the above flags. For example, File.new("test.txt", "rb") would open test.txt in read-only mode as a binary file.)
"t"Text file mode. (This flag may only appear in conjunction with the above flags. For example, File.new("test.txt", "wt") would open test.txt in write-only mode as a text file.)

Writing a string to a file

A string can be written to a file with an instance of the File class.

file = File.new('tmp.txt', 'w')
file.write("NaNaNaNa\n")
file.write('Batman!\n')
file.close

The File class also offers a shorthand for the new and close operations with the open method.

File.open('tmp.txt', 'w') do |f|
  f.write("NaNaNaNa\n")
  f.write('Batman!\n')
end

For simple write operations, a string can be also written directly to a file with File.write. Note that this will overwrite the file by default.

File.write('tmp.txt', "NaNaNaNa\n" * 4 + 'Batman!\n')

To specify a different mode on File.write, pass it as the value of a key called mode in a hash as another parameter.

File.write('tmp.txt', "NaNaNaNa\n" * 4 + 'Batman!\n', { mode: 'a'})

Open and closing a file

Manually open and close a file.

# Using new method
f = File.new("test.txt", "r") # reading
f = File.new("test.txt", "w") # writing
f = File.new("test.txt", "a") # appending

# Using open method
f = open("test.txt", "r")

# Remember to close files
f.close

Automatically close a file using a block.

f = File.open("test.txt", "r") do |f|
  # do something with file f
  puts f.read # for example, read it
end

get a single char of input

Unlike gets.chomp this will not wait for a newline.

First part of the stdlib must be included

require 'io/console'

Then a helper method can be written:

def get_char
  input = STDIN.getch
  control_c_code = "\u0003"
  exit(1) if input == control_c_code
  input
end

Its' imporant to exit if control+c is pressed.

Reading from STDIN

# Get two numbers from STDIN, separated by a newline, and output the result
number1 = gets
number2 = gets
puts number1.to_i + number2.to_i
## run with: $ ruby a_plus_b.rb
## or:       $ echo -e "1\n2" | ruby a_plus_b.rb

Reading from arguments with ARGV

number1 = ARGV[0]
number2 = ARGV[1]
puts number1.to_i + number2.to_i
## run with: $ ruby a_plus_b.rb 1 2