Re[2]: Testing for null positional parameters.

[Tim Gray <tgray@xxxxxxxxxxxxxxxx>]

Hello Bruce,

Thank you.  I believe I will use the first one.  I hadn't thought
about using if/then because I hadn't flipped two pages back in the
book.

Thanks again.

--- 

 Tim   
 IT Technician
 ADAC Plastics, Inc.

---

Wednesday, January 10, 2001, 10:27:25 AM, you wrote:

>> I am writing a script that I will use to sort files, sometime making
>> hard links in multiple directories.  That part that I'm stuck on is
>> the subject of this message, testing for null positional parameters.
>> 
>> if
>>   test $n "is not null" (where n is the number of the position)
>>        then
>>            command
>> fi

BS> There are a few options.

BS> You can test for the number of positional parameters with  $#
BS> So, if you pass the script three parameters,   $#  will be set to "3".
BS> If you don't pass it any parameters,  $#  will be "0".   etc.


BS> Or you can check like you are trying to do above like:

BS>     if [ -n "$3" ]; then
BS>         echo yes
BS>     else 
BS>         echo no
BS>     fi

BS> The "-n" checks for non-zero length, or "-z" checks for zero length.


BS> Or you can substitute non-set parameters to another value with:

BS> ${3:-value}

BS>   if [ ${3:-isnotset} = "isnotset" ]; then
BS>       echo parameter 3 is not set
BS>   else
BS>       echo parameter 3 is set to: $3
BS>   fi


BS> And there are a lot of other ways, but I posted my favorites.

BS> --------------------------------------------
BS> Bruce Smith                bruce@armintl.com
BS> System Administrator / Network Administrator
BS> Armstrong International, Inc.
BS> Three Rivers, Michigan  49093  USA
BS> http://www.armstrong-intl.com/
BS> --------------------------------------------