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20.9. Using Templates to Generate HTML
20.9.1. Problem
You
want to store a parameterized template in an external file, read that
template from your CGI script, and substitute your own variables for
escapes embedded in the text. This separates your program from the
static parts of the document.
20.9.2. Solution
To expand only variable references, use this
template
function:
sub template {
my ($filename, $fillings) = @_;
my $text;
local $/; # slurp mode (undef)
open(my $fh, "<", $filename) or return;
$text = <$fh>; # read whole file
close($fh); # ignore retval
# replace quoted words with value in %$fillings hash
$text =~ s{ %% ( .*? ) %% }
{ exists( $fillings->{$1} )
? $fillings->{$1}
: "
}gsex;
return $text;
}on a data file like this:
<!-- simple.template for internal template( ) function -->
<HTML><HEAD><TITLE>Report for %%username%%</TITLE></HEAD>
<BODY><H1>Report for %%username%%</H1>
%%username%% logged in %%count%% times, for a total of %%total%% minutes.
If you can guarantee the data file is secure from tampering, use the
CPAN module Text::Template to expand full expressions. A data file
for Text::Template looks like
this:
<!-- fancy.template for Text::Template -->
<HTML><HEAD><TITLE>Report for {$user}</TITLE></HEAD>
<BODY><H1>Report for {$user}</H1>
{ lcfirst($user) } logged in {$count} times, for a total of
{ int($total / 60) } minutes.
For a complete templating solution, see the Template Toolkit''s
Template module This offers a scripting language and mod_perl
integration, and is covered in Recipe 21.17.
20.9.3. Discussion
Parameterized output for your CGI scripts is a good idea for many
reasons. Separating your program from its data lets other people (art
directors, for instance) change the HTML but not the program. Even
better, two programs can share the same template, so style changes in
the template are immediately reflected in both programs'' output.For example, suppose you have the first template from the Solution
stored in a file. Then your CGI program contains the definition of
the template subroutine shown earlier and makes
appropriate settings for variables $username,
$count, and $total. You can
fill in the template by simply using:
%fields = (
username => $whats_his_name,
count => $login_count,
total => $minute_used,
);
print template("/home/httpd/templates/simple.template", \%fields);
The template file contains keywords surrounded by double percent
symbols (%%KEYWORD%%). These keywords are looked
up in the %$fillings hash whose reference was
passed as the second argument to template. Example 20-7 is a more elaborate example using an SQL
database.
Example 20-7. userrep1
#!/usr/bin/perl -w
# userrep1 - report duration of user logins using SQL database
use DBI;
use CGI qw(:standard);
# template( ) defined as in the Solution section above
$user = param("username") or die "No username";
$dbh = DBI->connect("dbi:mysql:connections:mysql.domain.com",
"connections", "seekritpassword") or die "Couldn''t connect\n";
$sth = $dbh->prepare(<<"END_OF_SELECT") or die "Couldn''t prepare SQL";
SELECT COUNT(duration),SUM(duration)
FROM logins WHERE username=''$user''
END_OF_SELECT
# this time the duration is assumed to be in seconds
if (@row = $sth->fetchrow_array( )) {
($count, $seconds) = @row;
} else {
($count, $seconds) = (0,0);
}
$sth->finish( );
$dbh->disconnect;
print header( );
print template("report.tpl", {
''username'' => $user,
''count'' => $count,
''total'' => $total
});
For a fancier, more flexible solution, look at the second template in
the Solution section, which relies upon the CPAN module
Text::Template. Contents of braces found within the template file are
evaluated as Perl code. Ordinarily, these substitutions are just
simple variables:
You owe: {$total}but they can also include full expressions:
The average was {$count ? ($total/$count) : 0}.Example 20-8 is an example of using that template.
Example 20-8. userrep2
#!/usr/bin/perl -w
# userrep2 - report duration of user logins using SQL database
use Text::Template;
use DBI;
use CGI qw(:standard);
$tmpl = "/home/httpd/templates/fancy.template";
$template = Text::Template->new(-type => "file", -source => $tmpl);
$user = param("username") or die "No username";
$dbh = DBI->connect("dbi:mysql:connections:mysql.domain.com",
"connections", "secret passwd") or die "Couldn''t db connect\n";
$sth = $dbh->prepare(<<"END_OF_SELECT") or die "Couldn''t prepare SQL";
SELECT COUNT(duration),SUM(duration)
FROM logins WHERE username=''$user''
END_OF_SELECT
$sth->execute( ) or die "Couldn''t execute SQL";
if (@row = $sth->fetchrow_array( )) {
($count, $total) = @row;
} else {
$count = $total = 0;
}
$sth->finish( );
$dbh->disconnect;
print header( );
print $template->fill_in( );
But this approach raises security concerns. Anyone who can write to
the template file can insert code that your program will run. See
Recipe 8.17 for ways to lessen this danger.
20.9.4. See Also
The documentation for the CPAN modules Text::Template and Template;
Recipe 8.16; Recipe 14.9
