$re = '/\{\{ *(ab|cd|ef|gh) *\}\} *\{\{ *(ab|cd|ef|gh) *\}\} *(\{\{ *(ab|cd|ef|gh) *\}\})* *(\{\{ *(ab|cd|ef|gh) *\}\})* *(\{\{ *(ab|cd|ef|gh) *\}\})* *(\{\{ *(ab|cd|ef|gh) *\}\})*/m';
$str = '{{ab}}{{ab}}{{ab}}{{ab}}{{ab}}{{ab}}
{{ab}} {{ab}} {{ab}} {{ab}} {{ab}} {{ab}}
machintruc {{ab}} {{cd}}
{{ab}} {{cd}} {{ef}} [https://truc.org truc]
{{ab}}{{ cd }}{{ ef }} {{ gh }} {{ gh }}{{lien web|url=tr.uc}}
{{mr}} Trucmuche
';
$subst = "{{mul|$1|$2|$4|$6|$8|$10}} ";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php