What is the difference between % and %% in a cmd file?
batch-file, cmd
Solution
(Explanation in more details can be found in an archived Microsoft KB article.)
Three things to know:
- The percent sign is used in batch files to represent command line parameters: `%1`, `%2`, ...
Two percent signs with any characters in between them are interpreted as a variable:
`echo %myvar%`
- Two percent signs without anything in between (in a batch file) are treated like a single percent sign in a command (not a batch file): `%%f`
Why's that?
For example, if we execute your (simplified) command line
FOR /f %f in ('dir /b .') DO somecommand %f
in a batch file, rule 2 would try to interpret
%f in ('dir /b .') DO somecommand %
as a variable. In order to prevent that, you have to apply rule 3 and escape the `%` with an second `%`:
FOR /f %%f in ('dir /b .') DO somecommand %%f
Problem
I recently included a line similar to this in a .cmd file: ``` for /f %%f in ('dir /b .\directory\*.sql') DO sqlcmd -b -o ".\directory\output\%%f.txt" -i ".\directory\%%f" ``` Originally I had only used %f, and it would work fine when run on the command line, but not when run through the file. When I switched to %%f, it worked in the file. Just wondering what the difference is.