China DOS Union

Today I saw a command like this in some DOS books, but I don't understand exactly how it is used, and I don't really understand what it means either. I'd like the experts to give me some guidance!!

1。 The batch file below will repeatedly display the contents of several specified files:
c:\>type demo2.bat
for %%x in (%1 %2 %3 %4) do type %%X
c:\>
What I want to ask is;
1。 %1 %2 %3 %4 are originally parameters of the batch file, so what is the purpose of putting them inside the parentheses in the command above? How do we define the values of its parameters?

And also, I often see expressions like %cdrom%. What do the % signs on both sides mean? Under what circumstances can expressions like these be used? Please give me some guidance...

The % signs on both sides of cdrom indicate that it is an environment variable. That command means to display the contents of the files corresponding to the parameters entered as %1, %2, %3, and %4 when executing the batch file. For example, when you run DEMO2 *.TXT *.DOC *.BAT, it will automatically display the contents of those files.

Actually, parameters can also be layered within parameters!
It can be done like this: for example, a batch file named
"ab.bat"
@echo off
for %%a in (%1 %2 %3 %4) do type %%a
can be run like this:
c:\>ab 1.txt 2.txt 3.txt 4.txt

It also works directly on the command line
c:\>for %a in (%1 %2 %3 %4) do type %a 1.txt 2.txt 3.txt 4.txt

Re gotomsdos:

The command-line usage in post #3 is incorrect. On the command line, %1 and the like, which are command-line parameters used specifically for batch files, will not be parsed and escaped, thus causing the Type command's multiple-parameter error. Even though type in NT CMD can already allow multiple parameters, there would still be a syntax error because %1 cannot be recognized.