Using a percent sign (%) in a batch file requires that two percent
signs (%%) be specified.
For example, the command to display "5%" from a batch file would be :
MS-DOS uses %1, %2, ... %9 as replaceable command line parameters. For
example, before executing the command ECHO %1, %1 will be replaced
with the first parameter passed to the batch file. %0 is replaced with
the command used to execute the batch file.
A single percent sign on a line is treated as a "nul" character in a
batch file. For example:
ECHO % is processed as ECHO
ECHO a%b is processed as ECHO ab
If a command contains two percent signs, MS-DOS will treat any characters
between them as an environment variable to be expanded. For example, if the
SET command shows that the current environment variables are
ECHO %PATH% is processed as ECHO C:\DOS
ECHO a%b% is processed as ECHO aC
ECHO a%b b%a is processed as ECHO aa
If there are no characters between the two percent signs, one percent
sign is stripped off and the other will remain. This is why a FOR command
that echos the name of each file with a .COM extension would be
FOR %V IN (*.COM) DO ECHO %V
but if the same command is placed in a batch file, the following is
FOR %%V IN (*.COM) DO ECHO %%V
"Microsoft MS-DOS Batch File Quick Reference," Microsoft Press.