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===== JavaScript =====
===== JavaScript =====
Jennifer D. St Clair asks:
> Most of my pages contain JavaScript and Stylesheets.
> Most of my pages contain JavaScript and Stylesheets.
> How do I change the template identifier?
> How do I change the template identifier?
Jennifer is worried about the braces in the JavaScript being taken as the delimiters of the Perl program fragments. Of course, disaster will ensue when perl tries to evaluate these as if they were Perl programs. The best choice is to find some unambiguous delimiter strings that you can use in your template instead of curly braces, and then use the "DELIMITERS" option. However, if you can’t do this for some reason, there are two easy workarounds:
You can put "\" in front of "{", "}", or "\" to remove its special
meaning. So, for example, instead of
meaning. So, for example, instead of
}
}
you can put
if (br== "n3") \{
if (br== "n3") \{
\}
\}
and it’ll come out of the template engine the way you want.
But here is another method that is probably better. To see how it works, first consider what happens if you put this into a template:
{ ’foo’ }
{ ’foo’ }
Since it’s in braces, it gets evaluated, and obviously, this is going to turn into
foo
foo
So now here’s the trick: In Perl, "q{...}" is the same as '...'. So if we wrote
{q{foo}}
{q{foo}}
it would turn into
foo
foo
So for your JavaScript, just write
{q{if (br== "n3") {
{q{if (br== "n3") {
}
}
and it’ll come out as
if (br== "n3") {
if (br== "n3") {
}
}
which is what you want.
===== Shut Up! =====
People sometimes try to put an initialization section at the top of their templates, like this:
{ ...
{ ...
}
}
Then they complain because there is a 17 at the top of the output that they didn’t want to have there.
Remember that a program fragment is replaced with its own return value, and that in Perl the return value of a code block is the value of the last expression that was evaluated, which in this case is 17. If it didn’t do that, you wouldn’t be able to write "{$recipient}" and have the recipient filled in.
To prevent the 17 from appearing in the output is very simple:
{ ...
{ ...
}
}
Now the last expression evaluated yields the empty string, which is invisible. If you don’t like the way this looks, use
{ ...
{ ...
}
}
instead. Presumably, $SILENTLY has no value, so nothing will be interpolated. This is what is known as a ‘trick’.
===== Compatibility =====
Every effort has been made to make this module compatible with older versions. The only known exceptions follow:
The output format of the default "BROKEN" subroutine has changed twice, most recently between versions 1.31 and 1.40.
Starting in version 1.10, the $OUT variable is arrogated for a special meaning. If you had templates before version 1.10 that happened to use a variable named $OUT, you will have to change them to use some other variable or all sorts of strangeness will result.
Between versions 0.1b and 1.00 the behavior of the \ metacharacter changed. In 0.1b, \\ was special everywhere, and the template processor always replaced it with a single backslash before passing the code to Perl for evaluation. The rule now is more complicated but probably more convenient. See the section on backslash processing, below, for a full discussion.
===== Backslash Processing =====
In "Text::Template" beta versions, the backslash was special whenever it appeared before a brace or another backslash. That meant that while "{"\n"}" did indeed generate a newline, "{"\\"}" did not generate a backslash, because the code passed to Perl for evaluation was "\" which is a syntax error. If you wanted a backslash, you would have had to write "{"\\\\"}".
In "Text::Template" versions 1.00 through 1.10, there was a bug: Backslash was special everywhere. In these versions, "{"\n"}" generated the letter "n".
The bug has been corrected in version 1.11, but I did not go back to exactly the old rule, because I did not like the idea of having to write "{"\\\\"}" to get one backslash. The rule is now more complicated to remember, but probably easier to use. The rule is now: Backslashes are always passed to Perl unchanged unless they occur as part of a sequence like "\\\\\\{" or "\\\\\\}". In these contexts, they are special; "\\" is replaced with "\", and "\{" and "\}" signal a literal brace.
Examples:
\{ foo \}
\{ foo \}
is not evaluated, because the "\" before the braces signals that they should be taken literally. The result in the output looks like this:
{ foo }
{ foo }
This is a syntax error:
{ "foo}" }
{ "foo}" }
because "Text::Template" thinks that the code ends at the first "}", and then gets upset when it sees the second one. To make this work correctly, use
{ "foo\}" }
{ "foo\}" }
This passes "foo}" to Perl for evaluation. Note there’s no "\" in the evaluated code. If you really want a "\" in the evaluated code, use
{ "foo\\\}" }
{ "foo\\\}" }
This passes "foo\}" to Perl for evaluation.
Starting with "Text::Template" version 1.20, backslash processing is disabled if you use the "DELIMITERS" option to specify alternative delimiter strings.
===== A short note about $Text::Template::ERROR =====
In the past some people have fretted about ‘violating the package boundary’ by examining a variable inside the "Text::Template" package. Don’t feel this way. $Text::Template::ERROR is part of the published, official interface to this package. It is perfectly OK to inspect this variable. The interface is not going to change.
If it really, really bothers you, you can import a function called "TTerror" that returns the current value of the $ERROR variable. So you can say:
use Text::Template ’TTerror’;
use Text::Template ’TTerror’;
}
}
I don’t see what benefit this has over just doing this:
use Text::Template;
use Text::Template;
or die "Couldn’t make template: $Text::Template::ERROR; aborting";
or die "Couldn’t make template: $Text::Template::ERROR; aborting";
But if it makes you happy to do it that way, go ahead.
===== Sticky Widgets in Template Files =====
The "CGI" module provides functions for ‘sticky widgets’, which are form input controls that retain their values from one page to the next. Sometimes people want to know how to include these widgets into their template output.
It’s totally straightforward. Just call the "CGI" functions from inside the template:
{ $q->checkbox_group(NAME => ’toppings’,
{ $q->checkbox_group(NAME => ’toppings’,
}
}
===== Automatic preprocessing of program fragments =====
It may be useful to preprocess the program fragments before they are evaluated. See "Text::Template::Preprocess" for more details.
===== Author =====
Mark-Jason Dominus, Plover Systems
Please send questions and other remarks about this software to "mjd-perl-template+@plover.com"
You can join a very low-volume (<10 messages per year) mailing list for announcements about this package. Send an empty note to "mjd-perl-tem-plate-request@plover.com" to join.
For updates, visit "http://www.plover.com/~mjd/perl/Template/".
===== Support? =====
This software is version 1.45. It may have bugs. Suggestions and bug reports are always welcome. Send them to "mjd-perl-tem-plate+@plover.com". (That is my address, not the address of the mailing list. The mailing list address is a secret.)
== LICENSE ==
== LICENSE ==
Text::Template version 1.45
Copyright (C) 2008 Mark Jason Dominus
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. You may also can redistribute it and/or modify it under the terms of the Perl Artistic License.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received copies of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
== THANKS ==
== THANKS ==
Many thanks to the following people for offering support, encouragement, advice, bug reports, and all the other good stuff.
David H. Adler / Joel Appelbaum / Klaus Arnhold / Antonio Araga~o / Kevin Atteson / Chris.Brezil / Mike Brodhead / Tom Brown / Dr. Frank Bucolo / Tim Bunce / Juan E. Camacho / Itamar Almeida de Carvalho / Joseph Cheek / Gene Damon / San Deng / Bob Dougherty / Marek Grac / Dan Franklin / gary at dls.net / Todd A. Green / Donald L. Greer Jr. / Michelangelo Grigni / Zac Hansen / Tom Henry / Jarko Hietaniemi / Matt X. Hunter / Robert M. Ioffe / Daniel LaLiberte / Reuven M. Lerner / Trip Lilley / Yannis Livassof / Val Luck / Kevin Madsen / David Marshall / James Mastros / Joel Meulenberg / Jason Moore / Sergey Myasnikov / Chris Nandor / Bek Oberin / Steve Palincsar / Ron Pero / Hans Persson / Sean Roehnelt / Jonathan Roy / Shabbir J. Safdar / Jennifer D. St Clair / Uwe Schneider / Randal L. Schwartz / Michael G Schwern / Yonat Sharon / Brian C. Shensky / Niklas Skoglund / Tom Snee / Fred Steinberg / Hans Stoop / Michael J. Suzio / Dennis Taylor / James H.Thompson / Shad Todd / Lieven Tomme / Lorenzo Valdettaro / Larry Virden / Andy Wardley / Archie Warnock / Chris Wesley / Matt Womer / Andrew G Wood / Daini Xie / Michaely Yeung
Special thanks to:
Jonathan Roy
for telling me how to do the "Safe" support (I spent two years worrying about it, and then Jonathan pointed out that it was trivial.)
Ranjit Bhatnagar
for demanding less verbose fragments like they have in ASP, for helping me figure out the Right Thing, and, especially, for talking me out of adding any new syntax. These discussions resulted in the $OUT feature.
Bugs and Caveats
"my" variables in "fill_in" are still susceptible to being clobbered by template evaluation. They all begin with "fi_", so avoid those names in your templates.
The line number information will be wrong if the template’s lines are not terminated by "\n". You should let me know if this is a problem. If you do, I will fix it.
The $OUT variable has a special meaning in templates, so you cannot use it as if it were a regular variable.
There are not quite enough tests in the test suite.
