Reading specific lines from an external file in ruby IO

I have this code:

File.foreach("testfile.txt") { |line| print line }
lines = File.readlines("testfile.txt")
lines.each { |line| print line }

Ex. how could I edit this to get a specific line from testfile.txt ?

$text2 = gets("some code to give me text on line 2 from textfile.txt").chomp

So, I want to run a program that searches for 4 different variables that are editable by anyone. These will be in a separate file and thus the code will not have to be rewritten in order to change the test for a new set of search cases.

Say I have a document (I suppose text is easiest but am probably wrong) that looks like this:

Tea

Coffee

Hot Chocolate

Cookies
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That will be all that is in the file. And another file(.rb) pulls these variables and searches for them in Google or whatever. If the code reads in bytes then I wouldn't be able to change the variables to anything longer or shorter.

It would be feasible to have the document say

1:Tea

2:Coffee

3:Hot Chocolate

4:Cookies

So long as the code would only pull out the "Tea" or "coffee" and not the preceding number.

---

It sounds like you don't want to return a line that matches a certain pattern, but you want to grab by line number.

Solution 1:

def read_line_number(filename, number)
  return nil if number < 1
  line = File.readlines(filename)[number-1]
  line ? line.chomp : nil
end

Solution 2a - a bit more efficient because it doesn't try to read entire file:

require 'english'
def read_line_number_1a(filename, number)
  found_line = nil
  File.foreach(filename) do |line|
    if $INPUT_LINE_NUMBER == number
      found_line = line.chomp
      break
    end
  end
  found_line
end

Solution 2b - also efficient, but in a more functional style (though I haven't checked whether detect will read to end-of-file)

def read_line_number(filename, match_num)
  found_line, _idx =
    File.enum_for(:foreach, filename).each_with_index.detect do |_cur_line, idx|
      cur_line_num = idx+1
      cur_line_num == match_num
    end
  found_line.chomp
end

Usage:

text = read_line_number("testfile.txt", 2)

---

You would want to use lines.grep "some string". Or just lines[x] if you know exactly which line number x you want.

---

The solution I have is:

My testfile.txt reads

Yes
Yes is does
Man this is awesome

my .rb file reads

a = IO.readlines("testfile.txt").grep(/\w+/)
puts "does it work...."
sleep 2
puts a[2]
sleep 10

---

def read_line_number(filename, number)
f = File.open(filename)
l = nil
begin
  number.times do 
  l = f.readline.chomp
  end
rescue
puts "End of file reached"
else
f.close unless f.nil?
return l  
end
end