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Andy Wardley


Template::Manual::Filters - Standard filters


This section lists all the standard filters distributed with the Template Toolkit for post-processing output.



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


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...


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.


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.


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+', '_') %]




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.


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'.


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. If binmode is set, binary mode on STDOUT is turned on (see the binmode perl function.

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 <abw@kfs.org>



Template Toolkit version 2.04, released on 29 June 2001.


  Copyright (C) 1996-2001 Andy Wardley.  All Rights Reserved.
  Copyright (C) 1998-2001 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.