What happens during set "x=%y%" ?

[WernerGg]

I had a

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set x=%y%

somewhere in my code and the program did not work. I needed hours to find that my editor (TextPad) had left a space at the end of that line which was then appended to x.

Sometimes I saw code like

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set "x=%y%"

which I did not understand and which should be an error according to the specification of the SET statement, which is

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set [variable=[string]]

Q1: Is the reason for that kind of coding with string delimitters just to avoid the problem with trailing spaces?

Q2: What happens really during execution of that statement? Does the command interpreter just throw the apostrophes away? But take the second apostrophe as end-of-line?

Actually I can write

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set "x=any value" and then comments

Q3: Why is that legal?

Q4: Would it not be reasonable, if not compelling, to use that kind of coding always?

[aGerman]

I think jeb should answer your questions because he spends a lof of time to figure out how the command interpreter works.
Finally (as you probably found out by yourself) it is legal. It's useful to avoid trailing spaces as well as to protect you from problems caused by special characters like ^<>|&. If you want to use it it's important to know that you have to write the first double quote in front of the variable. In this case the variable value is everyting after the equal sign until the last double quote in this line.

Regards
aGerman

[jeb]

@aGerman: You have answered the question already.

The only thing left are two little tricks.

An exlamation trick while using delayed expansion
set "myVar=hel^lo" !
The appended exlamation mark forces the delayed phase to remove one more time the carets.
This can be usefull in automatic return statements
new functions: :chr, :asc, :asciiMap
Describes also return a value the perfect way.

The qutoed/unquote trick

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set ^"myVar=hello^

LF inserted"

So you can use quotes but also the caret escape for appending linefeeds

jeb