Perl command scalar forces the argument to be evaluated in scalar context, when it normally could be evaluated in list context.
This is usually very handy because when you evaluate any @array in scalar context, you get the length of the array. (Agreeably scalar(@array) isn't the most intuitive way of getting the length of array, though. Most newbies seem to use $#array-1 to get the array length... note, of course, that length(@array) doesn't work!)