Is the echo statement in php only output to the previous layer?

{Code...} if it only requires the value of $ url, why cannot it be referenced directly instead of using the echo statement? In my opinion, echo is only output to the upper layer. If it is output to the display at the outermost layer, it is output to the outer layer at the lower layer. Is that true? Php cainiao, sorry for your ignorance...

         
        The page stays for only one second ...... 

If you only need the value of $ url, why not directly reference it, but use the echo statement? In my opinion, echo is only output to the upper layer. If it is output to the display at the outermost layer, it is output to the outer layer at the lower layer. Is that true?
Sorry for your ignorance. I have checked the php manual and the answers are vague and cannot solve the problem.

Reply content:

         
        The page stays for only one second ...... 

If you only need the value of $ url, why not directly reference it, but use the echo statement? In my opinion, echo is only output to the upper layer. If it is output to the display at the outermost layer, it is output to the outer layer at the lower layer. Is that true?
Sorry for your ignorance. I have checked the php manual and the answers are vague and cannot solve the problem.

Echo-output one or more strings
Echo converts the following variables into strings and then outputs them to the file.
If you directly reference a variable that is not a string, it will be a tragedy.

Search for the difference between flush and ob_flush on the Internet.
Below is what I wrote

If there is aaa in 10 seconds, Can I guess that echo is output to the php "end" and it is not output to apache?
I am also a cainiao, maybe not.

Echo prints things into the output stream.
If executed locally, the output stream is the standard output (console)
If it is executed by the server, the output stream is a network stream.

The text outside the angle bracket label is equivalent to the original text.