Deleting a line in a textfile based on keyword in RUBY

Question

I am working on creating a program which stores users in a textfile, and would love to delete/modify a line based on a keyword. This is the code I have right now for searching a keyword, which in return will print the whole line containing the keyword:

        keyword = File.readlines('skier_info.txt')
        matches = keyword.select { |name| name[/#{search}/i] }

I'm wondering how I can use this small bit of code to write every line from the textfile over to a new one, except for the one line I get from the "matches" variable.

score 1 · Answer 1 · answered Dec 07 '16 at 14:20

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So you can already identify the line(s) you want to remove? That's 70% of the work. Almost there!

Now all you need to do is create a new file and write to it all lines from the existing file, except the ones you don't need. After you're done writing the new file, you can copy it over the old one.

answered Dec 07 '16 at 14:20

Sergio Tulentsev

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Thanks for the reply Sergio! I am very new to Ruby, so I don't know exactly how to do this... Could you please help me a bit more?:) – Vetle Ottem Frantzvaag Dec 07 '16 at 14:23
@VetleOttemFrantzvaag: being new is not an excuse for not using search. Take a look at this one: http://stackoverflow.com/questions/2777802/how-to-write-to-file-in-ruby – Sergio Tulentsev Dec 07 '16 at 14:25
Bad formulation by me. My problem is not writing a file, but how I would go through selecting each line from the file, except the one I searched for. – Vetle Ottem Frantzvaag Dec 07 '16 at 14:27
@VetleOttemFrantzvaag Ah, that's easy. Use `reject` instead of `select`. – Sergio Tulentsev Dec 07 '16 at 14:46

score 0 · Accepted Answer · edited May 23 '17 at 11:52

0

With the least amount of modification from your code :

keyword    = File.readlines('skier_info.txt')
no_matches = keyword.reject { |name| name[/#{search}/i] }

File.open('new_skier_info.txt','w+'){|out| out.puts no_matches}

reject is the opposite of select :

(1..10).reject{|x| x.even?}
=> [1, 3, 5, 7, 9]

If your input file is big and you don't want to read it all in memory :

File.open('new_skier_info.txt','w+') do |out| 
  File.foreach('skier_info.txt') do |line|
    out.puts line unless line =~ /#{search}/i
  end
end

You could also use grep -v in terminal ;)

edited May 23 '17 at 11:52

Community

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answered Dec 07 '16 at 14:55

Eric Duminil

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It's a bit unfortunate to read the entire file into memory when it's not necessary. – Jordan Running Dec 07 '16 at 21:52

Deleting a line in a textfile based on keyword in RUBY

2 Answers2