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SET ad =
SET /p ad = Do you want to [A] Allow or [D] Deny? 
ECHO "%ad%"

I type A and press Enter, and the output I get is:

Do you want to [A] Allow or [D] Deny?

Why doesn't it work?

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up vote 5 down vote accepted

You aren't setting %ad%. You are setting %ad %.

Some languages are more picky about whitespace than others. The cmd.exe script language is one of them – the syntax for setting a variable is set name=value, and if you add spaces around the =, they become part of the variable name and value.

If you're writing the script for Windows 7/8 only, I strongly recommend learning PowerShell instead. The language used by cmd.exe is awful.

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Note that PowerShell also comes with Vista. It's also available as a download for XP (and apparently as a recommended update, though I can't confirm). Note that there are different versions with varying features, though the basic syntax is the same. It's also far more powerful than the legacy command line (it supports .NET as far as any programming language, e.g. C# or VB.NET), though a bit heavier. – Bob Feb 10 '13 at 14:40
I didn't even know that variables could have spaces! This is the most ridiculous property of a language I've seen until now. I'm actually just using this to change some properties on a server, so I just want it to work as fast as possible.. – Student of Hogwarts Feb 10 '13 at 14:51
@StudentofHogwarts: You still haven't seen some interesting properties of PHP, or MUMPS, or FORTRAN... – grawity Feb 10 '13 at 16:44
@grawity Actually PHP was the first language I learned, and you are completely correct, there is a lot of (please pardon me, but this is actually right from the soul) crap in PHP. So I'm actually considering using Django instead, but I suppose it's more "okay" since that's what I've "grown up with".. – Student of Hogwarts Feb 10 '13 at 16:47
@StudentofHogwarts I've seen regular expressions that were a few pages long. – Mark Allen Feb 10 '13 at 21:17

The command processor in Windows 8 is unchanged from the one in Windows 7, as far as I know

Everything up to the equals sign is part of the variable name. So in this case, your variable name is actually "ad " without the quotes. You can view current environment variables with the command set without any parameters - this is very useful for debugging.

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