Pandoc::Filter(3) process Pandoc abstract syntax tree


The following filter "", adopted from pandoc scripting documentation <> converts level 2+ headers to regular paragraphs.

use Pandoc::Filter;
use Pandoc::Elements;
pandoc_filter Header => sub {
return unless $_->level >= 2;
return Para [ Emph $_->content ];

To apply this filter on a Markdown file:

    pandoc --filter -t markdown <

See <> for more examples of filters.


Pandoc::Filter is a port of pandocfilters <> from Python to modern Perl. The module provide provides functions to aid writing Perl scripts that process a Pandoc <> abstract syntax tree (AST) serialized as JSON. See Pandoc::Elements for documentation of AST elements.

This module is based on Pandoc::Walker and its function "transform". Please consider using its function interface ("transform", "query", "walk") instead of this module.


new( @actions | %actions )

Create a new filter with one or more action functions, given as code reference(s). Each function is expected to return an element, an empty array reference, or "undef" to modify, remove, or keep a traversed element in the AST. The current element is passed to an action function both as first argument and in the special variable $_. Output format (if specified) and document metadata are passed as second and third argument.

If actions are given as hash, key values are used to check which elements to apply for, e.g.

        Header                 => sub { ... }, 
        'Suscript|Superscript' => sub { ... }

apply( $ast [, $format [ $metadata ] ] )

Apply all actions to a given abstract syntax tree (AST). The AST is modified in place and also returned for convenience. Additional argument format and metadata are also passed to the action function. Metadata is taken from the Document by default (if the AST is a Document root).


Return a code reference to call all actions.


Return the number of actions in this filter.


The following functions are exported by default.

pandoc_walk( @actions | %actions )

Read a single line of JSON from STDIN and walk down the AST. Implicitly sets binmode UTF-8 for STDOUT.

pandoc_filter( @actions | %actions )

Read a single line of JSON from STDIN, apply actions and print the resulting AST as single line of JSON. This function is roughly equivalent to

    my $ast = Pandoc::Elements::pandoc_json(<>);
    Pandoc::Filter->new(@actions)->apply($ast, @ARGV ? $ARGV[0] : ());
    say $ast->to_json;

stringify( $ast )

Walks the ast and returns concatenated string content, leaving out all formatting. This function is also accessible as method of Pandoc::Element since version 0.12, so it will be removed as exportable function in a later version.


Copyright 2014- Jakob Vo╬▓

GNU General Public License, Version 2

This module is heavily based on Pandoc by John MacFarlane.