Sometimes, I use this notation:

my $cmd = [ cmd => ( opt => $val, opt => $val ) ];
[download]

In this case,

my $cmd = [ p4 => ( where => $savefile ) ];
[download]

It's probably overkill. Alternatives:

my $cmd = [ p4 => 'where', $savefile ];
my $cmd = [ qw( p4 where ), $savefile ];
my $cmd = [ 'p4', 'where', $savefile ];
[download]