Commandline parameters are values passed to the program from commandline when calling the program. For example:
$ perl sum.pl 4 5
sum.pl has two commandline arguments, 4 and 5.
All commandline parameters in Perl get inserted into the @ARGV array in the order they are typed. To access a values in the @ARGV array (for this example), we use $ARGV[0] and $ARGV[1].
#!/usr/bin/perl print $ARGV[0] + $ARGV[1];
This program returns the sum of the two arguments passed in the commandline.