Save values batch file

Question

I wrote this script to looking for volume with enough free space:

@echo on
setlocal
set gbsize=1,073,741,824
Set gbsize=%gbsize:,=%

for %%A in (A B C D) do          


        

Answer 1

Short answer:

Use

setlocal enabledelayedexpansion

instead of just setlocal and then use !bytesfree! to refer to the variable (just replace % by !).

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Longer answer:

This is because cmd expands variables as it parses a command, not when the command is run (which, obviously happens after parsing). A command in this case could also be a complete for statement including the block after it. So all instances of %bytesfree% within the loop are replaced by their value before the loop, which happens to be an empty string.

Delayed expansion is a special form of variable expansion which expands variables when a command is run instead of when parsing it. It can be enabled with

setlocal enabledelayedexpansion

(within a batch file) or

cmd /v:on

(for a complete session, but not in a batch file, unless you don't want it to resume).

Then the syntax !bytesfree! is used to refer to variables which are then expanded just prior to running a command. So when setting and using the same variable within a block (for loop, if, etc.) you pretty much always want to use delayed expansion.