File and I/O Operations

Parameters#

Flag	Meaning
“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

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