$re = '/\$_\.getArrayInstance\((?:\[([^;]*)\]|)\);/';
$str = 'var pdr_manager = $_.UNINITIALIZED();
var internalWidgets = $_.getArrayInstance();
var categorySelect= $_.UNINITIALIZED();
var operatorMap = $_.getArrayInstance([
\'EQUAL\': \'=\'
]);
firstColumnCheckBox: $_.getObjectInstance({
isEnabled: true,
allowMultipleSelection: true,
field: {\'Select\':nah},
width: 65
}),';
$subst = "[$1];";
$result = preg_replace($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