Request for translation (batch vertical bar)

I am requesting a translation in English words for the first line below/what it does.  I think it has something to do with an OR condition.  I would like to know exactly.

set /p d=Enter value: || set d=10000
echo %d%

Thanks.

Edited by hamluis, 21 March 2023 - 06:02 PM.
Moved from DOS to Programming - Hamluis.

I am requesting a translation in English words for the first line below/what it does.  I think it has something to do with an OR condition.  I would like to know exactly.

 

set /p d=Enter value: || set d=10000
echo %d%

Hello, it's been a while since I've written a serious batch script.

Assuming the script syntax is correct (it looks plausible to me), my English description for the script's behavior would be:

"

Display "Enter value:" to the user and allow them to provide input. 

If the user provides input, it is stored in variable "d". 

If the user doesn't provide input (presses ENTER without specifying a value), variable "d" is set to 10000.

Finally, the value stored in variable "d" is displayed

"

Explanation:

The script uses logical-OR (||) to simulate an if/else branch construct.

The first line is really two expressions separated by logical-OR:

set /p d=Enter value:

||

set d=10000

With logical-OR, only ONE sub-expression needs to be TRUE (non-zero) for the overall logical-OR expression to be TRUE.

This can lead to so-called "short circuit evaluation", where the script only executes logical-OR sub-expressions until it finds the FIRST TRUE sub-expression.

In your example, "set /p d=Enter value:" is the first sub-expression.  If the user enters a value it is stored in "d", but the sub-expression evaluates to a TRUE (non-zero) value (indicating the user entered something).  Because a TRUE value logical-ORed with anything is always TRUE, the script won't even bother evaluating the "set d=10000" sub-expression.

If, however, the script evaluates "set /p d=Enter value:" and the user doesn't enter a value, that sub-expression will evaluate to FALSE.  This FALSE sub-expression will force the logical-OR expression to evaluate subsequent sub-expression(s) (if any) until it finds one that is TRUE. In your example, the next sub-expression is set d=10000 and so "d" is set to 10000.

In this specific case the result of the logical-OR expression is not used.

In pseudo code, your script could be written as:

DISPLAY "ENTER VALUE:"

INPUT = GET_INPUT()

IF (INPUT IS NOT EMPTY)

{

 D = INPUT

}

ELSE

{

 D = 10000

}

Good luck and happy scripting

Your explanation is very detailed.  You took a lot of time to do so.  Thank-you, so much.

I knew it was something like that.  I have never come across the "||" before. 

This is what I was looking for...the "a-ha" part:  "If the user doesn't provide input (presses ENTER without specifying a value), variable "d" is set to 10000."

This is not the actual script I will be using, but a simplified example to make it easier for someone to explain.

Thanks, again.

No problem, happy to hear it was helpful.