Reading the First Line of a File in Ruby

Reading the first line of a file in Ruby

This will read exactly one line and ensure that the file is properly closed immediately after.

strVar = File.open('somefile.txt') {|f| f.readline}
# or, in Ruby 1.8.7 and above: #
strVar = File.open('somefile.txt', &:readline)
puts strVar

Ruby - how to read first n lines from file into array

Here is a one-line solution:

lines = File.foreach('file.txt').first(10)

I was worried that it might not close the file in a prompt manner (it might only close the file after the garbage collector deletes the Enumerator returned by File.foreach). However, I used strace and I found out that if you call File.foreach without a block, it returns an enumerator, and each time you call the first method on that enumerator it will open up the file, read as much as it needs, and then close the file. That's nice, because it means you can use the line of code above and Ruby will not keep the file open any longer than it needs to.

How to open and read a file in one line in ruby

File.read("/path/to/file")

It will read whole file content and return it as a result.

Skipping the first line when reading in a file in 1.9.3

Change each to each_with_index do |line, index| and next if index == 0 will work.

How do I read the nth line of a file efficiently in Ruby?

What about IO.foreach?

IO.foreach('filename') { |line| p line; break }

That should read the first line, print it, and then stop. It does not read the entire file; it reads one line at a time.

How to read lines of a file in Ruby

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.

In Ruby- Parsing Directory and reading first row of the file

Why are you assigning x to file_name? You can use file_name directly. And if you are only reading the first line of the file, why not try this?

#!/usr/bin/ruby

dir = "C:/fileload/src"
Dir.foreach(dir) do |file_name|
    full = File.join(dir, file_name)
    if File.file?(full)
        f = File.open(full)
        puts f.first
        f.close
    end
end

You should use File.join to safely combine paths in Ruby. I also checked that you are opening a file using the File.file? method.

Ruby continuously reading from beginning of file

The code you have written is quite unusual in Ruby programming, most of the time a file is read line by line using Enumerable methods, for example:

file.each { |line| [code here] }

That said you could use the Enumerable#cycle method to read the file more than one time. Given the following file, say foo.txt:

foo
bar

You can read it two times using the following code:

open('foo.txt') do |file|
  file.cycle(2) { |line| puts line }      
end

# Output:
#
# foo
# bar
# foo
# bar

If you pass nil, or no argument, to cycle it will read the file forever.

Ruby csv read first line in csv file

It should be false, not :false.

---

Related Topics