Pass regular expression as script argument Ruby

Question

I am trying to pass regular expression to process a file line by line. The regular expression works fine if I hard code it in the code, like this.

File.foreach(filename).with_index do |line, line_num|
  md5 = line.scan(/[0-9a-f]{32}/i)
  puts md5
end

This works wonderful and I can see every line that has a MD5 hash on it printed. Now, the problem comes when I try to pass the regular expression to match md5 hashes as a script argument like:

ruby md5.rb -h "/[0-9a-f]{32}/i"

options = {}
OptionParser.new do |opts|
  opts.on('-h', '--hash "<hash regex>"', 'Hash Regex') { |v| options[:hash] = v }
end.parse!

hash = options[:hash]
File.foreach(filename).with_index do |line, line_num|
  md5 = line.scan(hash)
  puts md5
end

Taryn East · Accepted Answer · 2015-11-03 03:43:27Z

1

You can pass the inside bits of the regex as a string, then convert it to a regex later eg:

ruby md5.rb -h "[0-9a-f]{32}"

To convert a string into a regex, just use interpolation:

regex = /#{regex_string}/i

answered Nov 3, 2015 at 3:43

Taryn East

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1 Comment

Michael Kohl Over a year ago

Instead of interpolation, you could also use Regexp.new(regex_string) which will throw a RegexpError if the expression is invalid.

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