Preg Grep和Backslashes

Question

I've got two arrays:

$array_plugins  = array(
            array( 'captcha\/captcha.php', 'Captcha', 'http://wordpress.org/extend/plugins/captcha/', 'http://bestwebsoft.com/plugin/captcha-plugin/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Captcha+bestwebsoft&plugin-search-input=Search+Plugins', 'admin.php?page=captcha.php' ), 
            array( 'contact-form-plugin\/contact_form.php', 'Contact Form', 'http://wordpress.org/extend/plugins/contact-form-plugin/', 'http://bestwebsoft.com/plugin/contact-form/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Contact+Form+bestwebsoft&plugin-search-input=Search+Plugins', 'admin.php?page=contact_form.php' ), 
            array( 'facebook-button-plugin\/facebook-button-plugin.php', 'Facebook Like Button Plugin', 'http://wordpress.org/extend/plugins/facebook-button-plugin/', 'http://bestwebsoft.com/plugin/facebook-like-button-plugin/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Facebook+Like+Button+Plugin+bestwebsoft&plugin-search-input=Search+Plugins', 'admin.php?page=facebook-button-plugin.php' ), 
            array( 'twitter-plugin\/twitter.php', 'Twitter Plugin', 'http://wordpress.org/extend/plugins/twitter-plugin/', 'http://bestwebsoft.com/plugin/twitter-plugin/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Twitter+Plugin+bestwebsoft&plugin-search-input=Search+Plugins', 'admin.php?page=twitter.php' ), 
            array( 'portfolio\/portfolio.php', 'Portfolio', 'http://wordpress.org/extend/plugins/portfolio/', 'http://bestwebsoft.com/plugin/portfolio-plugin/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Portfolio+bestwebsoft&plugin-search-input=Search+Plugins', '' ),
            array( 'gallery-plugin\/gallery-plugin.php', 'Gallery', 'http://wordpress.org/extend/plugins/gallery-plugin/', 'http://bestwebsoft.com/plugin/gallery-plugin/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Gallery+Plugin+bestwebsoft&plugin-search-input=Search+Plugins', '' ),
            array( 'adsense-plugin\/adsense-plugin.php', 'Google AdSense Plugin', 'http://wordpress.org/extend/plugins/adsense-plugin/', 'http://bestwebsoft.com/plugin/google-adsense-plugin/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Adsense+Plugin+bestwebsoft&plugin-search-input=Search+Plugins', 'admin.php?page=adsense-plugin.php' ),
            array( 'custom-search-plugin\/custom-search-plugin.php', 'Custom Search Plugin', 'http://wordpress.org/extend/plugins/custom-search-plugin/', 'http://bestwebsoft.com/plugin/custom-search-plugin/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Custom+Search+plugin+bestwebsoft&plugin-search-input=Search+Plugins', 'admin.php?page=custom_search.php' ),
            array( 'quotes_and_tips\/quotes-and-tips.php', 'Quotes and Tips', 'http://wordpress.org/extend/plugins/quotes-and-tips/', 'http://bestwebsoft.com/plugin/quotes-and-tips/', '/wp-admin/plugin-install.php?tab=search&type=term&s=Quotes+and+Tips+bestwebsoft&plugin-search-input=Search+Plugins', 'admin.php?page=quotes-and-tips.php' )
        );

and

Array ( [0] => advanced-code-editor/advanced-code-editor.php [1] => bigarray.php [2] => jamie-social-icons/jamie-social_icons.php [3] => nowwhat.php [4] => twitter-plugin/twitter.php )

When I use the code...

foreach($array_plugins as $plugins) {
          if( 0 < count( preg_grep( "/".$plugins[0]."/", $active_plugins ) ) ) {
                echo "hit";

I get one "hit" as a result. Why does preg_grep think that "twitter-plugin/twitter.php" and "twitter-plugin\/twitter.php" are the same string?

Answer 1

It's because \ got special meaning and is used to escape meta characters (see wiki article on escaping). For example if you'd like to match [ literaly, you need to escape it like \[ (and if you'd like to match \ then you need to escape it too => \\). For non meta characters escaping does nothing so \a equals a and \/ equals \/.

To fix this in your code simply replace

preg_grep( "/".$plugins[0]."/", $active_plugins )

with

preg_grep( "/". str_replace('\\', '\\\\', $pattern[0]) ."/", $active_plugins )

(double \\ here are due to escaping as well).