var_export just working for array, we need a repr equivalence for string

repr_equivalent_for_php_strings.php

<?php
/**
 * Created by PhpStorm.
 * User: Youi
 * Date: 7/25/2015
 * Time: 8:44 PM
 */

$s = "\x21\xff thing\n\t\\字";

echo str_represent($s);

function str_represent($str_var) {
    $unicode_leading_bits = array(
        '2' => "\x06",
        '3' => "\x0E",
        '4' => "\x1E",
        '5' => "\x3E",
        '6' => "\x7E"
    );

    $return_str = '';
    for ($i = 0, $len = strlen($str_var); $i < $len; $i++) {

        $char_value = ord($str_var[$i]);

        #check for the first byte of a unicode
        if (($char_value >> 7) !== 0) {
            foreach ($unicode_leading_bits as $in_sequence_bit_number => $in_sequence_bits) {

                $shift_number = 7 - $in_sequence_bit_number;

                #if current byte seems like a valid first byte, check for the following bytes.
                if (!(($char_value >> $shift_number) ^ ord($in_sequence_bits))) {

                    $byte_check  = true;
                    $temp_concat = '';

                    $largest_following_index = $i + $in_sequence_bit_number - 1;
                    if ($largest_following_index >= $len) break;

                    for ($following_byte_index = $i + 1; $following_byte_index <= $largest_following_index; $following_byte_index++) {
                        $byte_check &= (ord($str_var[$following_byte_index]) >> 6) === 2;
                        $temp_concat .= $str_var[$following_byte_index];
                    }

                    #a valid unicode character found!
                    if ($byte_check) {
                        $return_str .= $str_var[$i] . $temp_concat;
                        $i = $largest_following_index;
                        continue 2;
                    }

                }
            }

        }

        #not a unicode byte, this one should be a ascii byte
        if ($char_value < 127) {
            $return_str .= addcslashes($str_var[$i], "\0..\37\134");
        } else {
            $return_str .= sprintf('\x%02x', $char_value);
        }

    }

    return "\"$return_str\"";
}

made by this table https://en.wikipedia.org/wiki/UTF-8#Description