问题
when I'm running this script (from a .bat file):
set var1=true
if "%var1%"=="true" (
set var2=myvalue
echo %var2%
)
I always get:
ECHO is on.
Meaning the var2
variable was not really set.
Can anyone please help me understand why?
回答1:
var2 is set, but the expansion in the line echo %var2%
occurs before the block is executed.
At this time var2
is empty.
Therefore the delayedExpansion syntax exists, it uses !
instead of %
and it is evaluated at execution time, not parse time.
Please note that in order to use !
, the additional statement setlocal EnableDelayedExpansion
is needed.
setlocal EnableDelayedExpansion
set var1=true
if "%var1%"=="true" (
set var2=myvalue
echo !var2!
)
回答2:
I am a bit late to the party but another way to deal with this condition is to continue process outside if
, like this
set var1=true
if "%var1%"=="true" (
set var2=myvalue
)
echo %var2%
Or/and use goto
syntax
set var1=true
if "%var1%"=="true" (
set var2=myvalue
goto line10
) else (
goto line20
)
. . . . .
:line10
echo %var2%
. . . . .
:line20
This way expansion occurs "in time" and you don't need setlocal EnableDelayedExpansion
. Bottom line, if you rethink design of your script you can do it like that
来源:https://stackoverflow.com/questions/9102422/windows-batch-set-inside-if-not-working