Check out the following:

--$  cat argvtest.pl 
#!/usr/bin/perl -w 
###################################################################
use strict;

print "too few$/" if scalar(@ARGV) < 3 ;
print "just right$/" if scalar(@ARGV) == 3;
print "too many$/" if scalar(@ARGV) > 3;
--$  perl argvtest.pl 1 2
too few
--$  perl argvtest.pl 1 2 3
just right
--$  perl argvtest.pl 1 2 3 4
too many
--$
[download]

scalar is your friend! ;-)
HTH