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Text::Autoformat - Perl

You may have created your own templating system in Perl to meet certain project requirements, but did you know there is a better way? This article, the first in a five-part series, explores your options. It is excerpted from chapter three of Advanced Perl Programming, Second Edition, written by Simon Cozens (O'Reilly; ISBN: 0596004567). Copyright 2007 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.

TABLE OF CONTENTS:
  1. Templating Tools
  2. Formats and Text::Autoformat
  3. Text::Autoformat
  4. Text::Template
By: O'Reilly Media
Rating: starstarstarstarstar / 2
August 07, 2008

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There's a more 21st century way to deal with formatting, however, and that's the Text::Autoformat module. This has two main purposes--it wraps text more sensitively than the usual Text::Wrap module or the Unix fmt command, and it provides a syntactically simpler but more featureful replacement for the built-in format language.

Text::Autoformat's text wrapping capabilities are only tangentially related to templating, but they're still worth mentioning here.

The idea behind autoformat is to solve the problem of wrapping structured text; it was created specifically for email messages (with special consideration for quoted text, signatures, etc.), but it's applicable to any structured textual data. For instance, given the text:

  You have:
     * a splitting headache 
     *no tea 
     * your gown (being worn)
              It looks like your gown contains:
         . a thing your aunt gave you which you don't know what it is
         . a buffered analgesic
         . pocket fluff

fmt fails rather spectacularly:

  You have:
      
* a splitting headache * no tea * your gown
      (being worn)
       
It looks like your gown contains:
          . a thing your aunt gave you which
          you don't know what it is . a buffered
          analgesic . pocket fluff

In this case, the autoformat subroutine does things a lot better, as it looks ahead at the structure of the text it's formatting:

  You have:
      
* a splitting headache
      * no tea
      
* your gown (being worn) It looks like your
        gown contains:
          . a thing your aunt gave you which you
            
don't know what it is
          . a buffered analgesic
          . pocket fluff

Text::Autoformat's format language is quite similar to Perl's native one, but with some simplifications. First, the distinction between filling @ fields and continuing ^ fields is made by the choice of picture character, not the prefix to the field. Hence, what was:

  @<<<< @<<<<<<<<< @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< @<<<<<<<<<<<<<<<<<<<

now simply becomes:

  <<<<< <<<<<<<<<< <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< <<<<<<<<<<<<<<<<<<<<<

For continuation formats, you now use [ and ] , which repeat as necessary on subsequent lines:

Id      : <<<<<
Message : 
        [[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[

This will produce output like the following:

  Id      :    1
  Message :
          Hi Simon, Thank you for the supply of widgets that you sent me
          last week. I can assure you that they have all been put to good...

Unlike Perl's built-in continuation formats, however, be aware that the [and] lines repeat the entire format time and time again until the variable is completely printed out. So this, for instance, won't do what you expect:

  Id    : <<<<< [[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
[[[[[[[[[[[[[[[[[[[[

Instead, it'll produce output something like this:

Id

:

1

Hi Simon, Thank you for the supply of widgets that you sent

Id

:

 

me last week. I can assure you that they have all been put

Id

:

 

to good use, and have been found, as usual to be the very...

with even more spectacularly bad results for formats longer than one line.

One big advantage, though, is that with Text::Autoformat, formats are just plain strings instead of cleverly compiled patterns interleaved with code. These strings are processed with the form function, which needs to be exported specifically:

  use Text::Autoformat qw(form);

  my $format = <<EOF;
 
Id      : <<<<<
  Date    : <<<<<<<<
  From    : <<<<<<<<<<<<<<<<<<<<<
  Subject : <<<<<<<<<<<<<<<<<<<<<...
  EOF
  my $id = 10;
  my $date = "20/12/02";
  my $from = "Fred Foonly";
  my $subject = "Autoformatted message";
  print form($format, $id, $date, $from, $subject);

Text::Autoformat also provides extremely flexible control over the hyphenation of form fields in a multi-line block, including the ability to plug in other hyphenation routines such as Jan Pazdziora's TeX::Hyphen, the hyphenation algorithm used in Donald Knuth's TeX package. The main disadvantage, however, is that you don't get the same control over headers and footers as you would with write.

Both Perl formats and Text::Autoformat are great for producing formatted output in the style of 1980s form-based programs, but when people think of forms these days, they're more likely to think of things like form letters. Let's move on to look at modules that are more suited to this style of templating.



 
 
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