How to read lines of a file in Ruby

Question

I was trying to use the following code to read lines from a file. But when reading a file, the contents are all in one line:

line_num=0
File.open('xxx.txt').each do |line|
  print "#{line_num += 1} #{line}"
end

But this file prints each line separately.

---

I have to use stdin, like ruby my_prog.rb < file.txt, where I can't assume what the line-ending character is that the file uses. How can I handle it?

Answer 1

Ruby does have a method for this:

File.readlines('foo').each do |line|
    puts(line)
end

http://ruby-doc.org/core-1.9.3/IO.html#method-c-readlines

Answer 2

File.foreach(filename).with_index do |line, line_num|
   puts "#{line_num}: #{line}"
end

This will execute the given block for each line in the file without slurping the entire file into memory. See: IO::foreach.

Answer 3

Your first file has Mac Classic line endings (that’s "\r" instead of the usual "\n"). Open it with

File.open('foo').each(sep="\r") do |line|

to specify the line endings.

Answer 4

I'm partial to the following approach for files that have headers:

File.open(file, "r") do |fh|
    header = fh.readline
    # Process the header
    while(line = fh.gets) != nil
        #do stuff
    end
end

This allows you to process a header line (or lines) differently than the content lines.

Answer 5

It is because of the endlines in each lines. Use the chomp method in ruby to delete the endline '\n' or 'r' at the end.

line_num=0
File.open('xxx.txt').each do |line|
  print "#{line_num += 1} #{line.chomp}"
end

Answer 6

how about gets ?

myFile=File.open("paths_to_file","r")
while(line=myFile.gets)
 //do stuff with line
end

Answer 7

Don't forget that if you are concerned about reading in a file that might have huge lines that could swamp your RAM during runtime, you can always read the file piece-meal. See "Why slurping a file is bad".

File.open('file_path', 'rb') do |io|
  while chunk = io.read(16 * 1024) do
    something_with_the chunk
    # like stream it across a network
    # or write it to another file:
    # other_io.write chunk
  end
end