Problem of empty variable using set in Windows Batch

Question

set var=%1
echo var
set command=""
IF var==true ( 
    set command=dir
)

IF var==false ( 
    set command=dir /a
)
echo %command%
%command%

So, if I run this script by typing in

C:\>test true

the echo %command% always prints "". Any idea?

Answer 1

You are missing some % signs that are needed for any variable dereferencing.

You probably want it like this:

set var=%1
echo %var%
set command=""
IF %var%==true (                    <=== here
    set command=dir
)

IF %var%==false (                   <=== here
    set command=dir /a
)
echo %command%
%command%

You should also surround your string comparisons with quotes to allow for spaces, something like this:

IF "%var%"=="false"

Also, as Joey pointed out, clearing a variable is done by

set command=

without any quotes. Otherwise you will initialize the the variable with these quotes, leading to your weird output.