Advertisement
Advertisement


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?

2016/10/17
1
241
10/17/2016 5:50:25 PM

Accepted Answer

I believe my answer covers your new concerns about handling any type of line endings since both "\r\n" and "\r" are converted to Linux standard "\n" before parsing the lines.

To support the "\r" EOL character along with the regular "\n", and "\r\n" from Windows, here's what I would do:

line_num=0
text=File.open('xxx.txt').read
text.gsub!(/\r\n?/, "\n")
text.each_line do |line|
  print "#{line_num += 1} #{line}"
end

Of course this could be a bad idea on very large files since it means loading the whole file into memory.

2016/10/17
149
10/17/2016 5:52:05 PM


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.

2016/10/17

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.

2011/05/16

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.

2014/06/30

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
2014/06/30

how about gets ?

myFile=File.open("paths_to_file","r")
while(line=myFile.gets)
 //do stuff with line
end
2014/08/19

Source: https://stackoverflow.com/questions/6012930
Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Email: [email protected]