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You can also do this: array_of_lines = File.readlines(filename) Simple! Generally, you should try to use these shortcut methods wherever possible, as they result in shorter, easier-to-read code, and you don t have to worry about closing the files. Everything is taken care of for you in one step. Of course, if reading a file line by line is necessary (perhaps if you re working with extremely large files), then you can use the techniques demonstrated earlier in this chapter for reading line by line.

When reading a file, it can be useful to know where you are within that file. The pos method gives you access to this information: f = File.open("text.txt") puts f.pos puts f.gets puts f.pos

0 Fred Bloggs,Manager,Male,45 28 Before you begin to read any text from the file, the position is shown as 0. Once you ve read a line of text, the position is shown as 28. This is because pos returns the position of the file pointer (that is, the current location within the file that you re reading from) in the number of bytes from the start of the file. However, pos can work both ways, as it has a sister method, pos=: f = File.open("text.txt") f.pos = 8 puts f.gets puts f.pos

ggs,Manager,Male,45 28 In this instance, the file pointer was placed 8 bytes into the file before reading anything. This meant that Fred Blo was skipped, and only the rest of the line was retrieved.

The ability to jump easily around files, read lines based on delimiters, and handle data byte by byte makes Ruby ideal for manipulating data, but I haven t yet covered how to write new information to files or how to make changes to existing files.

Generally, you can mirror most of the techniques used to read files when writing to files. For example: File.open("text.txt", "w") do |f| f.puts "This is a test" end This code creates a new file (or overwrites an existing file) called text.txt and puts a single line of text within it. Previously, you ve used puts on its own to output data to the screen. However, when used with a File object, puts writes the data to the file instead. Simple! The "w" passed as the second argument to File.open tells Ruby to open the file for writing only, and to create a new file or overwrite what is already in the file. This is in contrast with the "r" mode used earlier when opening a file for reading only. However, you can use several different file modes, as covered in Table 9-1. table 9-1. File Modes Usable with File.new

Read-only. The file pointer is placed at the start of the file. Both reading and writing are allowed. The file pointer is placed at the start of the file. Write-only. A new file is created (or an old one overwritten as if new). Both reading and writing are allowed, but File.new creates a new file from scratch (or overwrites an old one as if new). Write (in append mode). The file pointer is placed at the end of the file and writes will make the file longer. Both reading and writing are allowed (in append mode). The file pointer is placed at the end of the file and writes will make the file longer. Binary file mode. You can use it in conjunction with any of the other modes listed. This mode is optional in Ruby 1.8 (except on Windows) but is required in Ruby 1.9 if you are reading files that are not just text.

Using the append mode described in Table 9-1, it s trivial to create a program that appends a line of text to a file each time it s run: f = File.new("logfile.txt", "a") f.puts Time.now f.close If you run this code multiple times, logfile.txt will contain several dates and times, one after the other. Append mode is particularly ideal for log file situations where new information has to be added at different times. The read and write modes work in a simple manner. If you want to open a file in a mode where it can be read from and written to at the same time, you can do just that: f = File.open("text.txt", "r+") puts f.gets f.puts "This is a test" puts f.gets f.close