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# Prefilters/Postfilters

Prefilter and postfilter plugins are very similar in concept; where they differ is in the execution -- more precisely the time of their execution.

``string smarty_prefilter_`name`` (string $source, object &$smarty)`

Prefilters are used to process the source of the template immediately before compilation. The first parameter to the prefilter function is the template source, possibly modified by some other prefilters. The plugin is supposed to return the modified source. Note that this source is not saved anywhere, it is only used for compilation.

``string smarty_postfilter_`name`` (string $compiled, object &$smarty)`

Postfilters are used to process the compiled output of the template (the PHP code) immediately after the compilation is done but before the compiled template is saved to the filesystem. The first parameter to the postfilter function is the compiled template code, possibly modified by other postfilters. The plugin is supposed to return the modified version of this code.

Example 16-7. prefilter plugin
`<?php /* * Smarty plugin * ------------------------------------------------------------- * File: prefilter.pre01.php * Type: prefilter * Name: pre01 * Purpose: Convert html tags to be lowercase. * ------------------------------------------------------------- */ function smarty_prefilter_pre01($source, &$smarty) { return preg_replace('!<(\w+)[^>]+>!e', 'strtolower("$1")', $source); } ?>`

Example 16-8. postfilter plugin
`<?php /* * Smarty plugin * ------------------------------------------------------------- * File: postfilter.post01.php * Type: postfilter * Name: post01 * Purpose: Output code that lists all current template vars. * ------------------------------------------------------------- */ function smarty_postfilter_post01($compiled, &$smarty) { $compiled = "<pre>\n<?php print_r(\$this->get_template_vars()); ?>\n</pre>" . $compiled; return $compiled; } ?>`

See also `register_prefilter()`, `unregister_prefilter()` `register_postfilter()`, `unregister_postfilter()`.

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