Create UTF-8 code from dynamic Unicode in PHP - php

Question

I am making a dynamic Unicode icon in PHP. I want the UTF-8 code of the Unicode icon.
So far I have done:
$value = "1F600";
$emoIcon = "\u{$value}";
$emoIcon = preg_replace("/\\\\u([0-9A-F]{2,5})/i", "&#x$1;", $emoIcon);
echo $emoIcon; //output 😀
$hex=bin2hex($emoIcon);
echo $hex; // output 26237831463630303b
$hexVal=chunk_split($hex,2,"\\x");
var_dump($hexVal); // output 26\x23\x78\x31\x46\x36\x30\x30\x3b\x
$result= "\\x" . substr($hexVal,0,-2);
var_dump($result); // output \x26\x23\x78\x31\x46\x36\x30\x30\x3b
But when I put the value directly, it prints the correct data:
$emoIcon = "\u{1F600}";
$emoIcon = preg_replace("/\\\\u([0-9A-F]{2,5})/i", "&#x$1;", $emoIcon);
echo $emoIcon; //output 😀
$hex=bin2hex($emoIcon);
echo $hex; // output f09f9880
$hexVal=chunk_split($hex,2,"\\x");
var_dump($hexVal); // output f0\x9f\x98\x80\x
$result= "\\x" . substr($hexVal,0,-2);
var_dump($result); // output \xf0\x9f\x98\x80

Answer 1

\u{1F600} is a Unicode escape sequence used in double-quoted strings, it must have a literal value - trying to use "\u{$value}", as you've seen, doesn't work (for a couple reasons, but that doesn't matter so much.)
If you want to start with "1F600" and end up with 😀 use hexdec to turn it into an integer and feed that to IntlChar::chr to encode that code point as UTF-8. E.g.:
$value = "1F600";
echo IntlChar::chr(hexdec($value));
Outputs:
😀