Parsing lines of text from external file in Ruby

Question

I am trying to parse a raw email. The desired result is a hash of the lines that contain specific headers.

This is the Ruby file:

raw_email = File.open("sample-email.txt", "r")
parsed_email = Hash.new('')

raw_email.each do |line|
  puts line
  header = line.chomp(":")
  puts header
  if header == "Delivered-To"
    parsed_email[:to] = line
  elsif header == "From"
    parsed_email[:from] = line
  elsif header == "Date"
    parsed_email[:date] = line
  elsif header == "Subject"
    parsed_email[:subject] = line
  end
end

puts parsed_email

And this is the raw email:

Delivered-To: [email protected]
From: John Doe <[email protected]>
Date: Tue, 12 Dec 2017 13:30:14 -0500
Subject: Testing the parser
To: [email protected]
Content-Type: multipart/alternative; 
boundary="123456789abcdefghijklmnopqrs"

--123456789abcdefghijklmnopqrs
Content-Type: text/plain; charset="UTF-8"

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer nec 
odio. Praesent libero. Sed cursus ante dapibus diam. Sed nisi. Nulla 
quis sem at nibh elementum imperdiet. Duis sagittis ipsum.

--123456789abcdefghijklmnopqrs
Content-Type: text/html; charset="UTF-8"

<div dir="ltr">Lorem ipsum dolor sit amet, consectetur adipiscing 
elit. Integer nec odio. Praesent libero. Sed cursus ante dapibus diam. 
Sed nisi. Nulla quis sem at nibh elementum imperdiet. Duis sagittis 
ipsum.<br clear="all">
</div>

--089e082c24dc944a9f056028d791--

The puts statements are just for my own testing to see if data is being passed along.

What I am getting is each full line put twice and an empty hash put at the end.

I have also tried changing different bits to strings or arrays and I've also tried using line.split(":", 1) instead of line.chomp(":")

Can someone please explain why this isn't working?

Chomp removes trailing characters (default is the newline). You want both: line.chomp.split(":") — Mark Thomas
– Mark Thomas, Commented Dec 13, 2017 at 13:28
I see. I was under the impression chomp would "split" at the last found supplied (or default) delimiter in a string and then drop everything after (including the delimiter). — Josh
– Josh, Commented Dec 13, 2017 at 14:05
BTW, your current approach is completely broken for folded header bodies. — Jörg W Mittag
– Jörg W Mittag, Commented Dec 13, 2017 at 16:42

Abdullah · Accepted Answer · 2017-12-13 14:00:48Z

1

Try this

raw_email = File.open("sample-email.txt", "r")
parsed_email = {}

raw_email.each do |line|
  case line.split(":")[0]
  when "Delivered-To"
    parsed_email[:to] = line
  when "From"
    parsed_email[:from] = line
  when "Date"
    parsed_email[:date] = line
  when "Subject"
    parsed_email[:subject] = line
  end
end

puts parsed_email
=> {:to=>"Delivered-To: [email protected]\n", :from=>"From: John Doe <[email protected]>\n", :date=>"Date: Tue, 12 Dec 2017 13:30:14 -0500\n", :subject=>"Subject: Testing the parser\n"}

Explanation You need to split line on : and select first. Like this line.split(":")[0]

edited Dec 13, 2017 at 14:00

answered Dec 13, 2017 at 13:43

Abdullah

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4 Comments

Josh Over a year ago

Of course. I tried it exactly like that originally, but forgot that split returns an array so I had left off the [0]. That led me down a rabbit hole of confusion. Thank you so much. This is exactly what I was trying to do.

Mark Thomas Over a year ago

This being said, I recommend using a mail parsing gem and not doing it yourself.

Josh Over a year ago

LOL. I completely agree. Normally I would, but, I'm trying to learn how mail parsing works. ;)

Danny_ds Over a year ago

Also: the scan should stop after the first blank line (which marks the end of the headerblock). This avoids scanning the full body (including any attachments), which can be large -- or the body could even contain matching fields which would produce wrong results.

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