What does the percent sign (% and %%) in a batch file argument mean?

Question

I think I'm missing something because I can't seem to find what this means.

Example:

for /D %%A in (*) do "\7za.exe" u -t7z -m9=LZMA2 "%%A.7z" "%%A"

That line was supposed to use a command line version of 7zip to compress individual folders, but I'm stumped as to what %%A means in this context.

[What is the difference between % and %% in a cmd file?](http://stackoverflow.com/questions/14509652/what-is-the-difference-between-and-in-a-cmd-file) — slhck, Nov 07 '13 at 17:26
Got command line and bath file confused. Changed the sign on top. — Jim Kieger, Nov 08 '13 at 02:32

score 15 · Accepted Answer · edited Oct 27 '14 at 07:45

15

The for command needs a placeholder so you can pass along variables for use later in the query, we are telling it use the placeholder %A, the reason the code you saw uses %%A is because inside a batch file (which I assume is where you found this) the % has a special meaning, so you must do it twice %% so it gets turned in to a single % to be passed to the for command

To actually break apart what the command is doing, there is two parts to the command:

 for /D %%A in (*) do .....

What this part says is for every folder in the current folder execute the following command replacing %%A with the name of the currently processing folder.

..... "\7za.exe" u -t7z -m9=LZMA2 "%%A.7z" "%%A"

What this part says is execute the command "\7za.exe" u -t7z -m9=LZMA2 "%%A.7z" "%%A" and replace the two %%A's with the current record we are processing.

edited Oct 27 '14 at 07:45

DavidPostill

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answered Nov 07 '13 at 17:27

Scott Chamberlain

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Just to nitpick - the /D on the for loop will limit the * wildcard to directories, not "every file in this folder and every subfolder" (assuming Command Extensions are enabled). – ernie Nov 07 '13 at 17:35
@ernie you are correct, I was looking at the /R switch on the help page, I have corrected my answer. – Scott Chamberlain Nov 07 '13 at 17:36
Thank you for that, it shows how noobish this seems, but it's pretty archaic stuff that I have to dig through a couple online manuals for. – Jim Kieger Nov 07 '13 at 17:48

score 0 · Answer 2 · answered Nov 07 '13 at 17:26

It's a variable.

That particular example uses the directory option of a FOR loop, iterating through the directories and assigning them to %%A.

That's also not a command-line example, but a batch file example. In batch files, you need to use %%A, while on the command-line, you'd just use %A.

score 0 · Answer 3 · answered Nov 07 '13 at 18:09

In your scenario, the %%A is a placeholder for what the "for" loop is iterating over (which the /D indicates directories). So each iteration of the loop, %%A is one of the directories.

You'll see %% instead of % in batch code. You'll see % instead of %% used in your command prompt.

So know that if you copy over a batch file code into a command prompt and run it with %% being used, it will error, and vice versa.

What does the percent sign (% and %%) in a batch file argument mean?

3 Answers3

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