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Cleaning the output of a converter

18 Nov 2011

When I worked at a small web design company, we often had clients bringing us a MS Word, Excel, or PDF file that must be published on web. Not as a downloadable file, but as a web page integrated into their site.

Microsoft Word certainly can save files in HTML, but the resulting code was bloated and different from our design. What we needed was a simple HTML that our designer could edit and style. How could Aba S&R help us?

Here is a DOC file saved in HTML:

<h3 align=center style='text-align:center;'><b><span style='font-size:10.0pt;font-family:"Arial";'>Lorem ipsum</span></b></h3>

<p class=Normal align=justify style='text-indent:14.0pt;text-align:justify;'><span style='font-family:"Times New Roman";'>Lorem ipsum dolor sit <i>amet,</i> consectetur adipisicing elit.</span></p>

We need to remove all attributes and <span> tags:

<h3><b>Lorem ipsum</b></h3>

<p>Lorem ipsum dolor sit <i>amet,</i> consectetur adipisicing elit.</p>

The following replacements can be used:

Search for: <(p|h1|h2|h3) [^>]*>
Replace with: <\1>

Search for: <span [^>]*>
Replace with: (nothing)

Search for: </span>
Replace with: (nothing)

[^>]* matches everything up to the next closing angle bracket >, and \1 means the text inside the first parentheses (in our case, the tag name).

Remove HTML attributes with regular expressions

Generally, I often used Aba to clean the output of a converter. For one client, I had to convert dozens of PDF files with technical specifications to HTML. There was a lot of formatting (subscripts, superscripts, tables), so I could not simply copy-and-paste it. There also were errors, for example, the letter O instead of zero in subscripts. Without Aba, I would not clean this mess.

Is it a bad practice?

Two redditors criticized my previous post about using regular expressions to replace HTML tags.

I fully agree that regexes should never be used to parse an arbitrary HTML code, for example, an HTML code entered by user. Never do this in your scripts; it's unreliable and insecure.

But what if you need to replace all relative links (/blog/) in your own code with absolute links (http://www.example.com/blog/), because you are moving some parts of your site to a subdomain (http://myproduct.example.com). Would you craft a script that parses your HTML code (carefully skipping <?php tags — Python's HTMLParser cannot do that), searches for all <a> tags with the href attribute, replaces the links, and saves the result to a file?

Or would you toss off a regex in a search-and-replace tool?

Would you write 43 lines of Python code or one-line regex for an ad-hoc replacement?

This is a blog about Aba Search and Replace, a tool for replacing text in multiple files.