my $argCount = $#ARGV+1;

To find the number of elements in an array, use the array in scalar context.

 my $argCount = @ARGV;

To find out how this is different (and why it is the *correct* way) read about the variable $[ by doing a perldoc perlvar

The sample code will illustrate that.

use strict;

$[ = 2;

my @num = ( 1..4 );

print "No of elements >> ", $#num+1, "\n";
print "No of elements >> ", scalar @num, "\n";
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Ouput

No of elements >> 6
No of elements >> 4

 $# is actually the last subscript of the array and the variable  $[ sets the base subscript to 2 (default is zero). To access the elements in @num you will have to use subscripts 2,3,4,5 and that is the reason you get '6' in the first case (5+1) and not '4' which is the actual number of elements.

Agree that when you dont reset $[ both the methods are same. Why use a complex last subscript+1 calculation when there is an easier way to find the number of elements that works in *all* cases ??