Perl

$r = 1; for(1           # r gets one for one
.. pop @ARGV) { $r *=   # to pop arg v r splat gets
$_; } print $r;         # the default print r

Toss this into a file named 'f.pl' (doesn't matter, just how I ran it below)

And the output:

$ perl f.pl 0
1$ perl f.pl 3
6$ perl f.pl 10
3628800$

Perl

$r = 1; for(1           # r gets one for one
.. pop @ARGV) { $r *=   # to pop arg v r splat gets
$_; } print $r;         # the default print r

Toss this into a file named f.pl

And the output:

$ perl f.pl 3
6$ perl f.pl 1-1
1$ perl f.pl 10
3628800$ 

Which is read as:

perl f p l three
perl f p l one less one
perl f p l ten

Perl

$r = 1; for(1         # r is one for one
.. $ARGV[0]) { $r *=  # to arg v zero r times equals
$_; } print $r;       # the default print r

Toss this into a file named 'f.pl' (doesn't matter, just how I ran it below)

And the output:

$ perl f.pl 0
1$ perl f.pl 3
6$ perl f.pl 10
3628800$

Perl

$r = 1; for(1           # r gets one for one
.. pop @ARGV) { $r *=   # to pop arg v r splat gets
$_; } print $r;         # the default print r

Toss this into a file named 'f.pl' (doesn't matter, just how I ran it below)

And the output:

$ perl f.pl 0
1$ perl f.pl 3
6$ perl f.pl 10
3628800$