Template::Filters - Post-processing filters for template blocks


    use Template::Filters;

    $filters = Template::Filters->new(\%config);

    ($filter, $error) = $filters->fetch($name, \@args, $context);


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.



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 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.


The following list details the configuration options that can be provided to the Template::Filters new() constructor.


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.


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.


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({


The following standard filters are distributed with the Template Toolkit.


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 %]


    <!-- This is a block of text filtered        -->
    <!-- through the above format.               -->


Folds the input to UPPER CASE.

    [% "hello world" FILTER upper %]




Folds the input to lower case.

    [% "Hello World" FILTER lower %]


    hello world


Folds the first character of the input to UPPER CASE.

    [% "hello" FILTER ucfirst %]




Folds the first character of the input to lower case.

    [% "HELLO" FILTER lcfirst %]




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 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 %]


    The cat sat on the mat


Converts the characters '<', '>' and '&' to '&lt;', '&gt;' and '&amp;', respectively, protecting them from being interpreted as representing HTML tags or entities.

    [% FILTER html %]
    Binary "<=>" returns -1, 0, or 1 depending on...
    [% END %]


    Binary "&lt;=&gt;" returns -1, 0, or 1 depending on...


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 'é' to '&eacute;'). 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


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 %]


    The cat sat on the mat.

    Mary had a little lamb.

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 %]


    The cat sat on the mat.
    Mary had a little lamb.


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 %]


    The cat sat on the mat.<br>
    Mary had a little lamb.<br>


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 %]



Note that URI escaping isn't always enough when generating hyperlinks in an HTML document. The & character, for example, is valid in a URI and will not be escaped by the URI filter. In this case you should also filter the text through the 'html' filter.

    <a href="[% filename | uri | html %]">click here</a>


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 %]


    ME> blah blah blah
    ME> cabbages, rhubard, onions


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 %]


    I have much to say...


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!


    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!


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+') %]



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+', '_') %]



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/${}.html") %]
          [% INCLUDE userinfo %]
       [% END %]
    [% END %]

or more succinctly, using side-effect notation:

    [% INCLUDE userinfo 
         FILTER redirect("users/${}.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.


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.


The stderr filter prints the output generated by the enclosing block to STDERR.


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.png | stdout(1);

Notice the use of the stdout filter to ensure that a particular expression generates output to stdout (in this case in binary mode).


Passes the text block to LaTeX and produces either PDF, DVI or PostScript output. The 'outputType' argument determines the output format and it should be set to one of the strings: "pdf" (default), "dvi", or "ps".

The text block should be a complete LaTeX source file.

    [% FILTER latex("pdf") -%]


    \title{A Sample TT2 \LaTeX\ Source File}
    \author{Craig Barratt}

    This is some text.

    [% END -%]

The output will be a PDF file. You should be careful not to prepend or append any extraneous characters or text outside the FILTER block, since this text will wrap the (binary) output of the latex filter. Notice the END directive uses '-%]' for the END_TAG to remove the trailing new line.

One example where you might prepend text is in a CGI script where you might include the Content-Type before the latex output, eg:

    Content-Type: application/pdf

    [% FILTER latex("pdf") -%]
    [% END -%]

In other cases you might use the redirect filter to put the output into a file, rather than delivering it to stdout. This might be suitable for batch scripts:

    [% output = FILTER latex("pdf") -%]
    [% END; output | redirect("document.pdf", 1) -%]

(Notice the second argument to redirect to force binary mode.)

Note that the latex filter runs one or two external programs, so it isn't very fast. But for modest documents the performance is adequate, even for interactive applications.

A error of type 'latex' will be thrown if there is an error reported by latex, pdflatex or dvips.


Andy Wardley <>


2.78, distributed as part of the Template Toolkit version 2.14, released on 04 October 2004.


  Copyright (C) 1996-2004 Andy Wardley.  All Rights Reserved.
  Copyright (C) 1998-2002 Canon Research Centre Europe Ltd.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


Template, Template::Context, Template::Manual::Filters

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