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Template::Filters(3pm) User Contributed Perl Documentation Template::Filters(3pm)
NAME
Template::Filters - Post-processing filters for template blocks
SYNOPSIS
use Template::Filters;
$filters = Template::Filters->new(\%config);
($filter, $error) = $filters->fetch($name, \@args, $context);
DESCRIPTION
The Template::Filters module implements a provider for creating and/or returning
subroutines that implement the standard filters. Additional custom filters may be
provided via the FILTERS options.
METHODS
new(\%params)
Constructor method which instantiates and returns a reference to a Template::Filters
object. A reference to a hash array of configuration items may be passed as a parameter.
These are described below.
my $filters = Template::Filters->new({
FILTERS => { ... },
});
my $template = Template->new({
LOAD_FILTERS => [ $filters ],
});
A default Template::Filters module is created by the Template.pm module if the
LOAD_FILTERS option isn't specified. All configuration parameters are forwarded to the
constructor.
$template = Template->new({
FILTERS => { ... },
});
fetch($name, \@args, $context)
Called to request that a filter of a given name be provided. The name of the filter
should be specified as the first parameter. This should be one of the standard filters or
one specified in the FILTERS configuration hash. The second argument should be a
reference to an array containing configuration parameters for the filter. This may be
specified as 0, or undef where no parameters are provided. The third argument should be a
reference to the current Template::Context object.
The method returns a reference to a filter sub-routine on success. It may also return
(undef, STATUS_DECLINE) to decline the request, to allow delegation onto other filter
providers in the LOAD_FILTERS chain of responsibility. On error, ($error, STATUS_ERROR)
is returned where $error is an error message or Template::Exception object indicating the
error that occurred.
When the TOLERANT option is set, errors are automatically downgraded to a STATUS_DECLINE
response.
CONFIGURATION OPTIONS
The following list details the configuration options that can be provided to the
Template::Filters new() constructor.
FILTERS
The FILTERS option can be used to specify custom filters which can then be used with
the FILTER directive like any other. These are added to the standard filters which
are available by default. Filters specified via this option will mask any standard
filters of the same name.
The FILTERS option should be specified as a reference to a hash array in which each
key represents the name of a filter. The corresponding value should contain a
reference to an array containing a subroutine reference and a flag which indicates if
the filter is static (0) or dynamic (1). A filter may also be specified as a solitary
subroutine reference and is assumed to be static.
$filters = Template::Filters->new({
FILTERS => {
'sfilt1' => \&static_filter, # static
'sfilt2' => [ \&static_filter, 0 ], # same as above
'dfilt1' => [ \&dyanamic_filter_factory, 1 ],
},
});
Additional filters can be specified at any time by calling the define_filter() method
on the current Template::Context object. The method accepts a filter name, a
reference to a filter subroutine and an optional flag to indicate if the filter is
dynamic.
my $context = $template->context();
$context->define_filter('new_html', \&new_html);
$context->define_filter('new_repeat', \&new_repeat, 1);
Static filters are those where a single subroutine reference is used for all
invocations of a particular filter. Filters that don't accept any configuration
parameters (e.g. 'html') can be implemented statically. The subroutine reference is
simply returned when that particular filter is requested. The subroutine is called to
filter the output of a template block which is passed as the only argument. The
subroutine should return the modified text.
sub static_filter {
my $text = shift;
# do something to modify $text...
return $text;
}
The following template fragment:
[% FILTER sfilt1 %]
Blah blah blah.
[% END %]
is approximately equivalent to:
&static_filter("\nBlah blah blah.\n");
Filters that can accept parameters (e.g. 'truncate') should be implemented
dynamically. In this case, the subroutine is taken to be a filter 'factory' that is
called to create a unique filter subroutine each time one is requested. A reference
to the current Template::Context object is passed as the first parameter, followed by
any additional parameters specified. The subroutine should return another subroutine
reference (usually a closure) which implements the filter.
sub dynamic_filter_factory {
my ($context, @args) = @_;
return sub {
my $text = shift;
# do something to modify $text...
return $text;
}
}
The following template fragment:
[% FILTER dfilt1(123, 456) %]
Blah blah blah
[% END %]
is approximately equivalent to:
my $filter = &dynamic_filter_factory($context, 123, 456);
&$filter("\nBlah blah blah.\n");
See the FILTER directive for further examples.
TOLERANT
The TOLERANT flag is used by the various Template Toolkit provider modules
(Template::Provider, Template::Plugins, Template::Filters) to control their behaviour
when errors are encountered. By default, any errors are reported as such, with the
request for the particular resource (template, plugin, filter) being denied and an
exception raised. When the TOLERANT flag is set to any true values, errors will be
silently ignored and the provider will instead return STATUS_DECLINED. This allows a
subsequent provider to take responsibility for providing the resource, rather than
failing the request outright. If all providers decline to service the request, either
through tolerated failure or a genuine disinclination to comply, then a '<resource>
not found' exception is raised.
DEBUG
The DEBUG option can be used to enable debugging messages from the Template::Filters
module by setting it to include the DEBUG_FILTERS value.
use Template::Constants qw( :debug );
my $template = Template->new({
DEBUG => DEBUG_FILTERS | DEBUG_PLUGINS,
});
TEMPLATE TOOLKIT FILTERS
The following standard filters are distributed with the Template Toolkit.
format(format)
The 'format' filter takes a format string as a parameter (as per printf()) and formats
each line of text accordingly.
[% FILTER format('<!-- %-40s -->') %]
This is a block of text filtered
through the above format.
[% END %]
output:
<!-- This is a block of text filtered -->
<!-- through the above format. -->
upper
Folds the input to UPPER CASE.
[% "hello world" FILTER upper %]
output:
HELLO WORLD
lower
Folds the input to lower case.
[% "Hello World" FILTER lower %]
output:
hello world
ucfirst
Folds the first character of the input to UPPER CASE.
[% "hello" FILTER ucfirst %]
output:
Hello
lcfirst
Folds the first character of the input to lower case.
[% "HELLO" FILTER lcfirst %]
output:
hELLO
trim
Trims any leading or trailing whitespace from the input text. Particularly useful in
conjunction with INCLUDE, PROCESS, etc., having the same effect as the TRIM configuration
option.
[% INCLUDE myfile | trim %]
collapse
Collapse any whitespace sequences in the input text into a single space. Leading and
trailing whitespace (which would be reduced to a single space) is removed, as per trim.
[% FILTER collapse %]
The cat
sat on
the mat
[% END %]
output:
The cat sat on the mat
html
Converts the characters '<', '>', '&' and '"' to '<', '>', '&', and '"'
respectively, protecting them from being interpreted as representing HTML tags or
entities.
[% FILTER html %]
Binary "<=>" returns -1, 0, or 1 depending on...
[% END %]
output:
Binary "<=>" returns -1, 0, or 1 depending on...
html_entity
The html filter is fast and simple but it doesn't encode the full range of HTML entities
that your text may contain. The html_entity filter uses either the Apache::Util module
(which is written in C and is therefore faster) or the HTML::Entities module (written in
Perl but equally as comprehensive) to perform the encoding. If one or other of these
modules are installed on your system then the text will be encoded (via the escape_html()
or encode_entities() subroutines respectively) to convert all extended characters into
their appropriate HTML entities (e.g. converting 'A~X' to 'é'). If neither module
is available on your system then an 'html_entity' exception will be thrown reporting an
appropriate message.
For further information on HTML entity encoding, see
http://www.w3.org/TR/REC-html40/sgml/entities.html.
html_para
This filter formats a block of text into HTML paragraphs. A sequence of two or more
newlines is used as the delimiter for paragraphs which are then wrapped in HTML <p>...</p>
tags.
[% FILTER html_para %]
The cat sat on the mat.
Mary had a little lamb.
[% END %]
output:
<p>
The cat sat on the mat.
</p>
<p>
Mary had a little lamb.
</p>
html_break / html_para_break
Similar to the html_para filter described above, but uses the HTML tag sequence <br><br>
to join paragraphs.
[% FILTER html_break %]
The cat sat on the mat.
Mary had a little lamb.
[% END %]
output:
The cat sat on the mat.
<br>
<br>
Mary had a little lamb.
html_line_break
This filter replaces any newlines with <br> HTML tags, thus preserving the line breaks of
the original text in the HTML output.
[% FILTER html_line_break %]
The cat sat on the mat.
Mary had a little lamb.
[% END %]
output:
The cat sat on the mat.<br>
Mary had a little lamb.<br>
uri
This filter URI escapes the input text, converting any characters outside of the permitted
URI character set (as defined by RFC 2396) into a %nn hex escape.
[% 'my file.html' | uri %]
output:
my%20file.html
The uri filter correctly encodes all reserved characters, including "&", "@", "/", ";",
":", "=", "+", "?" and "$". This filter is typically used to encode parameters in a URL
that could otherwise be interpreted as part of the URL. Here's an example:
[% path = 'http://tt2.org/example'
back = '/other?foo=bar&baz=bam'
title = 'Earth: "Mostly Harmless"'
%]
<a href="[% path %]?back=[% back | uri %]&title=[% title | uri %]">
The output generated is rather long so we'll show it split across two lines:
<a href="http://tt2.org/example?back=%2Fother%3Ffoo%3Dbar%26
baz%3Dbam&title=Earth%3A%20%22Mostly%20Harmless%22">
Without the uri filter the output would look like this (also split across two lines).
<a href="http://tt2.org/example?back=/other?foo=bar
&baz=bam&title=Earth: "Mostly Harmless"">
In this rather contrived example we've manage to generate both a broken URL (the repeated
"?" is not allowed) and a broken HTML element (the href attribute is terminated by the
first """ after "Earth: " leaving "Mostly Harmless"" dangling on the end of the tag in
precisely the way that harmless things shouldn't dangle). So don't do that. Always use the
uri filter to encode your URL parameters.
However, you should not use the uri filter to encode an entire URL.
<a href="[% page_url | uri %]"> # WRONG!
This will incorrectly encode any reserved characters like ":" and "/" and that's almost
certainly not what you want in this case. Instead you should use the url (note spelling)
filter for this purpose.
<a href="[% page_url | url %]"> # CORRECT
Please note that this behaviour was changed in version 2.16 of the Template Toolkit.
Prior to that, the uri filter did not encode the reserved characters, making it
technically incorrect according to the RFC 2396 specification. So we fixed it in 2.16 and
provided the url filter to implement the old behaviour of not encoding reserved
characters.
url
The url filter is a less aggressive version of the uri filter. It encodes any characters
outside of the permitted URI character set (as defined by RFC 2396) into %nn hex escapes.
However, unlike the uri filter, the url filter does not encode the reserved characters
"&", "@", "/", ";", ":", "=", "+", "?" and "$".
indent(pad)
Indents the text block by a fixed pad string or width. The 'pad' argument can be
specified as a string, or as a numerical value to indicate a pad width (spaces). Defaults
to 4 spaces if unspecified.
[% FILTER indent('ME> ') %]
blah blah blah
cabbages, rhubard, onions
[% END %]
output:
ME> blah blah blah
ME> cabbages, rhubard, onions
truncate(length,dots)
Truncates the text block to the length specified, or a default length of 32. Truncated
text will be terminated with '...' (i.e. the '...' falls inside the required length,
rather than appending to it).
[% FILTER truncate(21) %]
I have much to say on this matter that has previously
been said on more than one occasion.
[% END %]
output:
I have much to say...
If you want to use something other than '...' you can pass that as a second argument.
[% FILTER truncate(26, '…') %]
I have much to say on this matter that has previously
been said on more than one occasion.
[% END %]
output:
I have much to say…
repeat(iterations)
Repeats the text block for as many iterations as are specified (default: 1).
[% FILTER repeat(3) %]
We want more beer and we want more beer,
[% END %]
We are the more beer wanters!
output:
We want more beer and we want more beer,
We want more beer and we want more beer,
We want more beer and we want more beer,
We are the more beer wanters!
remove(string)
Searches the input text for any occurrences of the specified string and removes them. A
Perl regular expression may be specified as the search string.
[% "The cat sat on the mat" FILTER remove('\s+') %]
output:
Thecatsatonthemat
replace(search, replace)
Similar to the remove filter described above, but taking a second parameter which is used
as a replacement string for instances of the search string.
[% "The cat sat on the mat" | replace('\s+', '_') %]
output:
The_cat_sat_on_the_mat
redirect(file, options)
The 'redirect' filter redirects the output of the block into a separate file, specified
relative to the OUTPUT_PATH configuration item.
[% FOREACH user = myorg.userlist %]
[% FILTER redirect("users/${user.id}.html") %]
[% INCLUDE userinfo %]
[% END %]
[% END %]
or more succinctly, using side-effect notation:
[% INCLUDE userinfo
FILTER redirect("users/${user.id}.html")
FOREACH user = myorg.userlist
%]
A 'file' exception will be thrown if the OUTPUT_PATH option is undefined.
An optional 'binmode' argument can follow the filename to explicitly set the output file
to binary mode.
[% PROCESS my/png/generator
FILTER redirect("images/logo.png", binmode=1) %]
For backwards compatibility with earlier versions, a single true/false value can be used
to set binary mode.
[% PROCESS my/png/generator
FILTER redirect("images/logo.png", 1) %]
For the sake of future compatibility and clarity, if nothing else, we would strongly
recommend you explicitly use the named 'binmode' option as shown in the first example.
eval / evaltt
The 'eval' filter evaluates the block as template text, processing any directives embedded
within it. This allows template variables to contain template fragments, or for some
method to be provided for returning template fragments from an external source such as a
database, which can then be processed in the template as required.
my $vars = {
fragment => "The cat sat on the [% place %]",
};
$template->process($file, $vars);
The following example:
[% fragment | eval %]
is therefore equivalent to
The cat sat on the [% place %]
The 'evaltt' filter is provided as an alias for 'eval'.
perl / evalperl
The 'perl' filter evaluates the block as Perl code. The EVAL_PERL option must be set to a
true value or a 'perl' exception will be thrown.
[% my_perl_code | perl %]
In most cases, the [% PERL %] ... [% END %] block should suffice for evaluating Perl code,
given that template directives are processed before being evaluate as Perl. Thus, the
previous example could have been written in the more verbose form:
[% PERL %]
[% my_perl_code %]
[% END %]
as well as
[% FILTER perl %]
[% my_perl_code %]
[% END %]
The 'evalperl' filter is provided as an alias for 'perl' for backwards compatibility.
stdout(options)
The stdout filter prints the output generated by the enclosing block to STDOUT. The
'binmode' option can be passed as either a named parameter or a single argument to set
STDOUT to binary mode (see the binmode perl function).
[% PROCESS something/cool
FILTER stdout(binmode=1) # recommended %]
[% PROCESS something/cool
FILTER stdout(1) # alternate %]
The stdout filter can be used to force binmode on STDOUT, or also inside redirect, null or
stderr blocks to make sure that particular output goes to stdout. See the null filter
below for an example.
stderr
The stderr filter prints the output generated by the enclosing block to STDERR.
null
The null filter prints nothing. This is useful for plugins whose methods return values
that you don't want to appear in the output. Rather than assigning every plugin method
call to a dummy variable to silence it, you can wrap the block in a null filter:
[% FILTER null;
USE im = GD.Image(100,100);
black = im.colorAllocate(0, 0, 0);
red = im.colorAllocate(255,0, 0);
blue = im.colorAllocate(0, 0, 255);
im.arc(50,50,95,75,0,360,blue);
im.fill(50,50,red);
im.png | stdout(1);
END;
-%]
Notice the use of the stdout filter to ensure that a particular expression generates
output to stdout (in this case in binary mode).
latex(outputType)
The latex() filter is no longer part of the core Template Toolkit distribution as of
version 2.15. You can download it as a separate Template-Latex distribution from CPAN.
AUTHOR
Andy Wardley <abw AT wardley.org>
<http://wardley.org/|http://wardley.org/>
VERSION
2.86, distributed as part of the Template Toolkit version 2.19, released on 27 April 2007.
COPYRIGHT
Copyright (C) 1996-2007 Andy Wardley. All Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
SEE ALSO
Template, Template::Context, Template::Manual::Filters
perl v5.10.0 2008-12-13 Template::Filters(3pm)
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