"%systemroot%" chages to "C:\windows"

[Mohammad_Dos]

I want to save "%systemroot" in C:\copy\jay.bat with batch file

i use it:
echo "%systemroot%" C:\copy\jay.bat"

but changes to C:\WINDOWS

what should i do?

[!k]

double %%

[Mohammad_Dos]

did not work

[dbenham]

from the command line:

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echo ^%systemroot^%

from within a batch file:

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echo %%systemroot%%

Dave Benham

[phillid]

Wouldn't one have to use the '>' or the '>>' symbols as well to put into the file?

[jeb]

from the command line:
Code:
echo ^%systemroot^%

from within a batch file:
Code:
echo %%systemroot%%

Within a batch file it's correct.

But from the command line it's only a hack, it isn't bullet proof,
as the caret doesn't escape a percent.
In reallity it only avoids the expansion.
Btw. the first caret is completly useless.
The second caret builds only an undefined variable name, and undefined variables stay unchanged on the command line.
But the carets are removed in the speacial character phase later so the result is
%systemroot%

And the trick fails if there is a variable named systemroot^

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set "systemroot^=fail"
echo ^%systemroot^%

fail

I didn't see a single command solution, only with a helper variable.

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set "helper=systemroot"
echo %%helper%%

jeb

[dbenham]

Wow - I had no idea I had stumbled on a hack.

I knew double percents don't work on the command line like they do in batch mode, and I was curious how to get the result on command line. "Escaping" the percent was the 1st thing I tried and it appeared to work.

It seems like a pretty good hack. I don't recall seeing ^ in a variable name very often.

Excellent explanation of how it actually works. Thanks jeb.

Based on jeb's explanation I realize the hack works if you put the ^ anywhere between the percents (as long as no variable is named that way):

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echo %^systemroot%
echo %system^root%
etc.

Dave Benham

[jeb]

Wow - I had no idea I had stumbled on a hack.

You are not alone
Even Microsoft didn't know it ...
Even the help at reg add /? recommends the hack.

jeb

[Mohammad_Dos]

what about this?

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%%a

changes to:

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%a