Question

I’m new to Ruby, I want to select some lines from a file that match a regex and then store to a list.

So I write the following code:

    def get_valid_instr istream
         p istream.select { |line| line.scan(/(^\s*\w+\s*;\s*\w+\s*$)/){|instr| instr[0].upcase.strip.split(";")}}
    end

   trace_instr = File.open("#{file_name}", "r"){|stream|  get_valid_instr stream}

The output is simply the display of all file.
If I put a print in scan block, I see exactly what I want.
There are other ways to do that (filling an external list) but I wonder why it doesn’t work and if there is ruby way.

Answer 1

If you pass a block to scan, it will return something different than if you don’t:

"abc".scan(/./)
# => ["a", "b", "c"]

"abc".scan(/./) {|l| puts l }
# a
# b
# c
# => "abc"

You need to be aware of this when using scan.

However, even better than your current solution would be to use grep. You can pass both your regular expression and your block to grep.