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Is a parse error an EXAMPLE of an error that OCCURS BEFORE THE SCRIPT IS EXECUTED?

https://www.php.net/manual/en/errorfunc.configuration.php#ini.error-reporting

Although display_errors may be set at runtime (with ini_set()), it won't have any effect if the script has fatal errors. This is because the desired runtime action does not get executed.

https://www.php.net/manual/en/function.set-error-handler.php

If errors occur before the script is executed (e.g. on file uploads) the custom error handler cannot be called since it is not registered at that time.

My doubt is because in 2 cases PHP mentions the term "before executing".

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    The PHP interpreter has to load and parse the file before it can be executed. So for example a simple missing semi-colon will break the parser, and it will never get to the execution step. Commented Nov 1, 2022 at 14:18
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    What documentation says is that you cannot use PHP code to change settings if: 1) The script is not valid so it's unable to run. 2) The setting you want to change affects something that already finished when the script starts running. Commented Nov 1, 2022 at 14:24
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    No, because it won't get that far. The PHP interpreter doesn't read and execute the script line by line, it has to load the whole script then parse it. Once it knows it's in a functional state, only then will it attempt to execute it. A try/catch block would be part of the execution, but a parse/syntax error breaks the readability. Commented Nov 1, 2022 at 14:28
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    Correct, because you cannot recover from it. Commented Nov 1, 2022 at 14:35
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    @aynber Indeed PHP has both: a compiler looks at the source code and generates opcodes; then an interpreter runs over those opcodes. Whether that makes the language as a whole "compiled" is a matter of debate and somewhat arbitrary definitions. But it's the compiler that is going to give you Parse Errors; if it was an interpreter, it would emit them as it reached each line or statement, not for the whole file. It felt like a useful enough distinction in this case to point out. Commented Nov 1, 2022 at 14:48

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PHP is not a directly interpreted language: your source code is processed first by a compiler. Specifically, when you tell PHP to execute a file, or include it with include/require, the entire file is parsed and compiled to an intermediate representation called "OpCodes". Only once the entire file has been compiled does any code in that file get executed (by running the OpCodes through an interpreter).

For that compilation to succeed, the syntax of the entire file needs to be correct. If it is not, a Parse Error will be generated.

If you are including a file, that error can be caught by the file which is calling include or require. But if the file being compiled is the one directly invoked by the web server or command-line command, there is no code "outside" that file which could catch the error, or change the settings relating to its display or handling.

When any error is not handled, PHP's last resort is simply to end the process - this is what is referred to as a "fatal error". In this case, the error can't be handled, so is always fatal; in most other cases, there is a chance to handle the error, and it only becomes fatal if you do not.

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excellent answer @IMSoP marked as a useful answer. "That's kind of important, since an interpreter is generally defined as something which doesn't look at a whole unit of code in advance." - because PHP parses the code in advance (because it is a compiler) it doesn't give you a chance to execute LITERALLY NO CODE? If it were an interpreter it would give a chance to execute some code, because an interpreter goes line by line (without giving a quick "glance") right?
@Daniel All generalisations are false, but yes some interpreters would allow you to make a syntax error on line 100 of a file, and only find out once lines 1 to 99 had been executed. Whether you think of that as "giving you a chance to run some code", or "telling you too late after some of the code has already run" is a matter of context. Also, as I mentioned, PHP in particular executes 1 file at a time, so you can run code before an include statement that reconfigures what will happen to a syntax error in the included file.

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