Basic IO Operations in Ruby

Discussion in 'Ruby on Rails' started by asha, Nov 1, 2012.

  1. asha

    asha New Member

    Nov 9, 2006
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    Ruby is one of the growing scripting & web development language, it was designed to be easy to learn and provides least possible surprises for a newcomer to the language. Ruby on Rails is a very popular and robust MVC web framework. Ruby can also be used as CGI or can be inserted into Apache as module with the help of mod_ruby.

    Ruby comes in many variants, but let's leave the details of that for another day, in this article we'll discuss how the basic input/output operations such a reading from the terminal, file, writing out to a file etc. can be done in Ruby.

    Reading from STDIN

    Ruby has a built-in function gets() which reads a line from a file handle, in this case the STDIN. Now, let's look at a simple code which will read a line from the STDIN and print it.

    # "print" because puts adds a trailing newline
    print "Enter your name: "
    # read a line into the variable name
    name = gets
    # print
    puts "Hello, #{name}"
    [pradeep@desktop]$ ./test.rb
    Enter your name: Pradeep
    Hello, Pradeep
    Let's look at another example where we'll ready the whole input line by line and print it's length.

    string = ''
    while line = gets
            string = string + line
    puts "Input was " + string.length.to_s + " character(s) long"
    [pradeep@desktop]$ ./test.rb
    The Quick Brown Fox Jumps Over The Lazy Dog
    Wow that was quick
    Input was 63 character(s) long
    [pradeep@desktop]$ ./test.rb < test.rb
    Input was 140 character(s) long

    Reading From A File

    The File object is contains the related operations for opening a file which returns the file handle object. Please follow the example below.

    # open the file for reading
    file_h ="data.txt", "r")
    # iterate till eof
    while line = file_h.gets
        puts line
    # close the filehandle
    Now, let me list a few file handle iterators which are unique to Ruby in the next example.

    # open the file for reading
    file_h ="data.txt", "r")
    # the each_byte method, reads character by character
    file_h.each_byte { |ch| putc ch }
    # the each_line method, reads line by line, default line separator is newline
    file_h.each_line { |line| puts "Read #{line.dump}" }
    # specify a different line separator
    file_h.each_line("|") do |line|
      puts "Read #{ line.dump }"
    # reading a specific no. of bytes, say reading 16 bytes
    data = file_h.sysread(16)
    # read the whole file into an array
    file_array = IO.readlines("data.txt")

    Writing To A File

    Writing to files with Ruby can be more fun than other languages, I guess it's because everything in Ruby is an object. There are numerous methods available to write to a file like print, printf, puts, syswrite, etc. all are called on the file handle. But remember not to mix syswrite and other methods, as syswrite works on a system level and is unbuffered, else set the file handle to be unbuffered by default. Now, follow the example below.

    # open the file for writing, you can also open it for appending with "a"
    # you may also specify the Unix file permissions for a new that would be created
    file_fh ='data.txt','w+', 0644)
    # set the file handle to turn of buffering, i.e. it will immediately write to the file
    file_fh.sync = true
    # write with puts, it'll append a newline in the end
    file_fh.puts("My first line")
    # write with print, it'll not add a newline
    file_fh.print("Add with print")
    # to see that there wasn't any newline added
    file_fh.print("Add with another print")
    # write any arbitrary string with syswrite, syswrite is faster than other methods
    # it returns the number of bytes written
    puts file_fh.syswrite("Trying syswrite")
    # remember to close the file, specially in case of buffered mode so that
    # any unbuffered data is written to the disk
    Hope this was helpful, enjoy coding in Ruby.

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