Eval function: \ Application

<? PHP $ string = "beautiful"; $ time = "Winter"; $ STR = 'this is a $ string $ Time Morning! '; Echo $ Str. "<br/> ";Eval ("\ $ STR = \" $ STR \";");Echo $ STR;?>
This is a model: eval ("xxx = xxx ;");
Eval is not a simple parameter, but a value assignment expression. You can think like this:
Step 1: Perform the value assignment operation
Step 2: run the assigned result in PHP code.
Focus on the right half of = first:
If this is the case,
Xxx = "$ Str", "$ Str" is treated as a string for operations
Xxx = \ "$ STR \", \ escaped ", $ STR is assigned as an object, which is exactly what we want
Then look at the left half of =:
Because it is a value assignment operation, add \
Finally:
Eval performs an operation on the final parameter $ STR to obtain the result.