Windows Batch Files if else

Question

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

User · Answer

You have to do the following   if   1              echo The variable is empty   ELSE       echo The variable contains  1

User · Answer

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

User · Answer

if not  1           must be  if not   1            If an argument isn t given  it s completely empty  not even     which represents an empty string in most programming languages   So we use the surrounding quotes to detect an empty argument

User · Answer

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

User · Answer

you have to do like this     if not  A 1      A    if the input argument  1 is null   your code will have problem

User · Answer

Another related tip is to use    1  instead of   1    Type  CALL     at the command line in Windows to get more details

[windows] Windows Batch Files: if else

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