Find strings and remove those lines

Question

I'm trying to read all the text files from a directory, iterate through every file, and search for strings in the file and delete those lines. Eg,

sample.txt

#Wrote for the configuration ideas

mag = some , db\m09oi, id\polki
jio = red\po9i8

[\]

@mag = denk
@jio = tea

I want to delete the lines having mag.

Output

#Wrote for the configuration ideas

jio = red\po9i8

[\]

@jio = tea

I tried:

Dir.glob("D:\\my_folder\\*.txt") do |file_name|

  value = File.read(file_name)
  change = value.gsub!(/[@m]ag/, "")
  File.open(file_name, "w") { |file| file.puts change }

end

But the lines aren't removed.

Any suggestions please.

Answer 1

It is better to read the file line by line and if a line contains mag, just omit it, and only write other lines to the new file. — Credits to @WiktorStribiżew

File.write(file_name, File.readlines(file_name).reject do |line|
                        line[/\bmag\b/]
                      end.join($/))

Here we read the file, split by lines with IO#readlines , reject lines having mag as a single word inside ( "magistrate" won't be matched,) join it back with the line delimiter, specified for this particular platform (eg \\n on unix) and write it back.