How to define an MS-DOS variable?

Question

Let's say I do the following in a CMD shell:

set FOO=bar 

Is there any way to define this variable other than recycling the CMD shell?

Answer 1

Yes, you can disable it with

 set FOO= 

Important Note. Make sure there are no trailing spaces / other invisible characters after the = character. set FOO= ! = set FOO=

Answer 2

A safe way to disable a variable is to use quotation marks as well, then there is no problem with trailing spaces.

 set FOO=bar echo %FOO% set "FOO=" text after the last quote is ignored echo %FOO% 

Answer 3

This works for me in my Windows 7 CMD shell:

 set FOO=bar echo %FOO% // bar set FOO= echo %FOO% // empty; calling "set" no longer lists it 

Answer 4

another method

 @Echo oFF setlocal set FOO=bar echo %FOO% endlocal echo %FOO% pause 

Note. This will not work on the interactive command line. But it works in batch mode script.

Answer 5

I would suggest the following only as a comment, but I think it is important enough to stand on my own.

Many previous answers mentioned that you need to beware of lagging spaces; and that's for sure. However, I found that sometimes trailing spaces just want to get there no matter what is especially important if you are running a single-line command line interface and need space as a command separator.

This is the solution to this problem:

 SET FOO=Bar echo %FOO% :: outputs Bar SET "FOO=" echo %FOO% :: outputs %FOO% 

By wrapping the ad in double quotation marks this way, the span issue can be completely eliminated. It can also be very useful when variables are created by concatenating to eliminate spaces between them - for example - paths, for example:

 SET A=c:\users\ && SET D=Daniel SET P="%a%%d%" ECHO %P% :: outputs "C:\Users\ Daniel" :: Notice the undesirable space there