for /f "delims=%file%" %%a in (aa1.txt) do echo del /f /s %%a%file%>>b.txt
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不应该用文件的扩展名作为分割字符
for命令的帮助里面有这样一段:
FOR /F "eol=; tokens=2,3* delims=, " %i in (myfile.txt) do @echo %i %j %k
    would parse each line in myfile.txt, ignoring lines that begin with
    a semicolon, passing the 2nd and 3rd token from each line to the for
    body, with tokens delimited by commas and/or spaces.  Notice the for
    body statements reference %i to get the 2nd token, %j to get the
    3rd token, and %k to get all remaining tokens after the 3rd.  For
    file names that contain spaces, you need to quote the filenames with
    double quotes.  In order to use double quotes in this manner, you also
    need to use the usebackq option, otherwise the double quotes will be
    interpreted as defining a literal string to parse.