[windows] Windows Batch Files: if else

I'm doing a simple batch file that requires one argument (you can provide more, but I ignore them).

For testing, this is what I have so far.

if not %1 == "" (
    dir /s/b %1
) else (
    echo no
)

Basically, I want to say if an argument is provided, recursively display all the files in the folder. Otherwise, say no.

It works when I provide an argument, but if I don't provide one it'll just tell me ( was unexpected at this time.

I mean, it works, but I wanted to at least display a user-friendly message explaining why it doesn't work. How should I change the code?

An alternative would be to set a variable, and check whether it is defined:

SET ARG=%1
IF DEFINED ARG (echo "It is defined: %1") ELSE (echo "%%1 is not defined")

Unfortunately, using %1 directly with DEFINED doesn't work.

you have to do like this...

if not "A%1" == "A"

if the input argument %1 is null, your code will have problem.

Another related tip is to use "%~1" instead of "%1". Type "CALL /?" at the command line in Windows to get more details.

Surround your %1 with something.

Eg:

if not "%1" == ""

Another one I've seen fairly often:

if not {%1} == {}

And so on...

The problem, as you can likely guess, is that the %1 is literally replaced with emptiness. It is not 'an empty string' it is actually a blank spot in your source file at that point.

Then after the replacement, the interpreter tries to parse the if statement and gets confused.

You have to do the following:

if "%1" == "" (
    echo The variable is empty
) ELSE (
    echo The variable contains %1
)