Check for null variable in Windows batch

Question

I m working on a Windows batch file that will bcp three text files into SQL Server  If something goes wrong in production  I want to be able to override the file names  So I m thinking of doing something like this   bcp exe MyDB  MyTable1 in  1 -SMyServer -T -c -m0 bcp exe MyDB  MyTable2 in  2 -SMyServer -T -c -m0 bcp exe MyDB  MyTable3 in  3 -SMyServer -T -c -m0   I would like to be able to enter default names for all three files  to be used if the positional parameters are not supplied  The idea would be either to execute   myjob bat   with no parameters  and have it use the defaults  or execute  myjob bat  c  myfile1   c  myfile2   c  myfile3    and have it use those files  I haven t been able to figure out how to tell if  1   2 and  3 exist and or are null  I also don t know how to set those values conditionally  Is this possible  Any suggestions would be appreciated

User · Answer

The right thing would be to use a  if defined  statement  which is used to test for the existence of a variable  For example    IF DEFINED somevariable echo Value exists   In this particular case  the negative form should be used   IF NOT DEFINED somevariable echo Value missing   PS  the variable name should be used without     caracters

User · Answer

To test for the existence of a command line paramater  use empty brackets   IF   1      echo Value Missing   or  IF   1  EQU    echo Value Missing   The SS64 page on IF will help you here  Under  Does  1 exist     You can t set a positional parameter  so what you should do is do something like  SET MYVAR  1   You can then re-set MYVAR based on its contents

User · Answer

Both answers given are correct  but I do mine a little different   You might want to consider a couple things     Start the batch with   SetLocal   and end it with  EndLocal   This will keep all your  SETs  to be only valid during the current session  and will not leave vars left around named like  FileName1  or any other variables you set during the run  that could interfere with the next run of the batch file   So  you can do something like   IF   1      SET FileName1 c  file1 txt   The other trick is if you only provide 1  or 2 parameters  use the SHIFT command to move them  so the one you are looking for is ALWAYS at  1     For example  process the first parameter  shift them  and then do it again   This way  you are not hard-coding  1   2   3  etc     The Windows batch processor is much more powerful than people give it credit for    I ve done some crazy stuff with it  including calculating yesterday s date  even across month and year boundaries including Leap Year  and localization  etc   If you really want to get creative  you can call functions in the batch processor     But that s really for a different discussion         Oh  and don t name your batch files  bat either    They are  cmd s now    heh    Hope this helps

User · Answer

Late answer  but currently the accepted one is at least suboptimal     Using quotes is ALWAYS better than using any other characters to enclose  1  Because when  1 contains spaces or special characters like  amp   the IF   1     simply stops with a syntax error     But for the case that  1 contains quotes  like in myBatch bat  my file txt   a simple IF   1        would fail     But as you can t know if quotes are used or not  there is the syntax   1  this removes enclosing quotes when necessary     Therefore  the code should look like   set  file1   1  IF    1      set  file1 default file   type   file1     --- always enclose your variables in quotes   If you have to handle stranger and nastier arguments like myBatch bat  This  amp  will    amp crash Then take a look at SO How to receive even the strangest command line parameters

User · Answer

rem set defaults  set filename1  c  file1 txt  set filename2  c  file2 txt  set filename3  c  file3 txt  rem set parameters  IF NOT  a 1    a   set filename1   1   IF NOT  a 2    a   set filename2   2   IF NOT  a 3    a   set filename1   3   echo  filename1    filename2    filename3    Be careful with quotation characters though  you may or may not need them in your variables

[windows] Check for null variable in Windows batch

Examples related to windows

Examples related to batch-file