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Mystery: Carets
Posted: 08 Sep 2010 03:33
by jeb
Can someone explain this?
Code: Select all
@echo off
setlocal EnableDelayedExpansion
set "^=one"
set "^^=two"
set "^"
set "caret=^"
call echo I have %%!caret!%% carets, but why?
You got
Code: Select all
^=one
^^=two
I have two carets, but why?
make a guess ...
jeb
Re: Mystery: Carets
Posted: 08 Sep 2010 05:20
by orange_batch
Because you touch yourself at night.
Are you asking for yourself, or to see if anyone knows? Either way, the command processor seems to double up the "string" caret before execution. No way around this...
Re: Mystery: Carets
Posted: 08 Sep 2010 08:54
by jeb
I know the answer.
You are near, but as you can see the solution is not so simple.
Code: Select all
setlocal EnableDelayedExpansion
set varE=^^!varE^^!#
set varP=%%varP%%#
set "caret=^"
call echo !caret!
You got only one ^
Re: Mystery: Carets
Posted: 08 Sep 2010 14:34
by miskox
Let me try it.
I will use BASIC, maybe in this way it will be easier to understand:
10 set ^="one"
20 set ^^="two"
30 set ^="" : rem Deletes variable ^
40 set caret=^ : rem variable caret gets the value of variable ^
50 print "..."
In line 50 variable from line 20 gets processed which is single caret because it is escaped by another caret.
Am I right?
Saso
Re: Mystery: Carets
Posted: 08 Sep 2010 16:40
by aGerman
!caret! is expanded to
^. The
CALL command doubles the
^. So you have
%^^% and this is expandet to
two.
_____________________________________________________________________________
jeb wrote:You got only one ^
Hmm, I think you got
echo ^^and this results to a single caret.
Regards
aGerman
Re: Mystery: Carets
Posted: 08 Sep 2010 19:03
by ghostmachine4
that's one of the problem with DOS. Caret (or other special characters ) should not be allowed to be used as variable names.
Re: Mystery: Carets
Posted: 09 Sep 2010 00:35
by jeb
aGerman wrote:!caret! is expanded to ^. The CALL command doubles the ^. So you have %^^% and this is expandet to two.
Yes this it is, but ...
Code: Select all
echo ^ zero
echo ^^ one caret
call echo !caret! one caret
call echo ^^ one caret
call echo ^^^^ two carets "^^^^" four carets
rem BUT NOW
call echo ^^^^ two carets "^^^^" eight carets (oho)
call call echo ^^^^ two carets "^^^^" sixteen carets (oh oh)
Each call doubles all carets in a line, also in quotes.
Normally, the carets are escaping themself, so a double caret is shrinking to one, but this does not work in quotes.
And as the escape-phase is after the % expanding phase you get the result of %%!caret!%% as
%^^%
Re: Mystery: Carets
Posted: 09 Sep 2010 12:19
by orange_batch
Haha jeb, a real DOS scientist. Bravo.