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POWhat is the smallest program possible to parse an email message header?
 

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  1. POWhat is the smallest program possible to parse an email message header?
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    <p>the homework: <a href="http://www.cs.rit.edu/~waw/networks/prob1.082.html" rel="nofollow noreferrer">http://www.cs.rit.edu/~waw/networks/prob1.082.html</a></p> <p>Ok, I am still confused why this question was asked for my data communications and networks class, but here is the question from my homework:</p> <blockquote> <ol start="8"> <li><p>Write a computer program that reads the header on an e-mail message and deletes all lines except those that begin with</p> <p>From:, To:, Subject: and Cc:.</p></li> </ol> <p>CONTEST -- Who can write the shortest program that does this.</p> </blockquote> <p>So after thinking for a bit I decided that the following Perl code was as small as I could do this.</p> <pre><code>#!/usr/bin/perl while (&lt;&gt;) { print "$_" if ($_ =~ m/^(To:|From:|Subject:|Cc:)/); } </code></pre> <p>All this does is act like a filter for which the only output is lines that start with From:, To:, Subject: and Cc: as specified in the question. Since there aren't any specific details I think that the above code works to at least correctly answer the question.</p> <p>Now, I wonder how small a program could possibly written for this? I can understand if no one wants to post code because they think I will use it for the assignment, but I am more or less looking for suggestions and techniques that could help me write the shortest program possible.</p> <p>Also, I am quite sure by shortest he is referring to actual code length. He did mention that scripting languages were the way to go so I doubt he is considering something like the overhead involved with an interpreter. This also means that he does not care which language is used.</p> <p>Thanks for looking!</p> <p>EDIT: Thanks for the suggestions! I had been reading questions here for quite a while, hopefully in the future I can contribute more. Also, some of the suggestions I trimmed my Perl code down to 55 bytes. I don't think we will need to deal with something like a multi-line header.</p> <p>BONUS: Who can identify a good reason why this was asked in a class where we are discussing things like packet switching and client/server architectures?</p> <p>EDIT2: For the record, my professor said that someone did this with something like 55 bytes. The only way I see that as being possible is if he was only asking for a simple implementation like the one above.</p>
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    1. COHow do you account for multi-lines headers ?
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    2. COAs for a good reason to ask it, header parsing is definitely relevant to packet routing. As for asking for small code, code size *can* potentially be of a concern depending on the hardware.
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    3. COThis fails to handle line folding. See section 2.2.3 of RFC 2822.
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      1. USbrian d foy
 

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