<?php
 
$input_str = 'Some text is here......[$radio_yes: He is eligible for PF. / $radio_no: He is not eligible for PF.]....Some text is here';
$control_name = 'radio_yes';
 
preg_match_all('/^(.*?)\[(.*?)\](.*?)$/si', $input_str, $matches, PREG_PATTERN_ORDER);
$before = $matches[1][0];
$controllerRaw = $matches[2][0];
$after = $matches[3][0];
 
preg_match_all("/$control_name:(.*?)\./si", $controllerRaw, $controller, PREG_PATTERN_ORDER);
$controller = $controller[1][0];
echo "$before $controller $after";
 

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