(`command`)

[tensaix2j]

is there any unix $() or `command` equivalent in DOS ?

for example: 

set %a% = `type b.txt`   so %a% will be assigned with stdout result of command `type b.txt` rather than taking the command `type b.txt` as string literally.   

[gpl]

From this page -> www.computerhope.com/forhlp.htm

There is this

Finally, you can use the FOR /F command to parse the output of a command. You do this by making the filenameset between the parenthesis a back quoted string. It will be treated as a command line, which is passed to a child CMD.EXE and the output is captured into memory and parsed as if it was a file. So the following example:

FOR /F "usebackq delims==" %i IN (`set`) DO @echo %i

would enumerate the environment variable names in the current environment.

I think this is what you were looking for
Graham