Mark-Jason Dominus' Text::Template has established itself as the de facto standard templating system for plain text. Its templating language is very simple indeed--anything between {and} is evaluated by Perl; everything else is left alone.

It is an object-oriented module--you create a template object from a file, filehandle, or string, and then you fill it in:

  use Text::Template;
  my $template = Text::Template->new(TYPE => "FILE",
                                     SOURCE => "email.tmpl");

  my $output = $template->fill_in();

So, let's say we've got the following template:

  Dear {$who},
      Thank you for the {$modulename} Perl module, which has saved me
  {$hours} hours of work this year. This would have left me free to play
  { int($hours*2.4) } games of go, which I would have greatly appreciated
  had I not spent the time goofing off on IRC instead.

  Love,
  Simon

We set up our template object and our variables, and then we process the template:

  use Text::Template;
  my $template = Text::Template->new(TYPE => "FILE",
                                     SOURCE => "email.tmpl");

  $who = "Mark";
  $modulename = "Text::Template";
  $hours = 15;
  print $template->fill_in();

And the output would look like:

  Dear Mark,
      Thank you for the Text::Template Perl module, which has saved me
  15 hours of work this year. This would have left me free to play
  36 games of go, which I would have greatly appreciated
  had I not spent the time goofing off on IRC instead.

  Love,
  Simon

Notice that the fill-in variables--$who, $modulename, and so on--are not my variables. When you think about it, this ought to be obvious--the my variables are not in Text::Template's scope, and therefore it wouldn't be able to see them. This is a bit unpleasant: Text::Template has access to your package variables, and you have to do a bit more work if you want to avoid giving use strict a fit.

Text::Template has two solutions to this. The first is pretty simple--just move the fill-in variables into a completely different package:

  use Text::Template;
  my $template = Text::Template->new(TYPE => "FILE",
                                     SOURCE => "email.tmpl");

  $Temp::who = "Mark";
  $Temp::modulename = "Text::Template"; 
  $Temp::hours = 15;
  print $template->fill_in(PACKAGE => "Temp");

That's slightly better, but it still doesn't please people for whom global variables are pure evil. If that's you, you can get around the problem by passing in a portable symbol table--that is, a hash:

  use Text::Template;
  my $template = Text::Template->new(TYPE => "FILE",
                                     SOURCE => "email.tmpl");

  print $template->fill_in(HASH => {
      who => "Mark",
      modulename => "Text::Template",
      hours => 15
  });

Please check back next week for the continuation of this article.