open (CMD, "your command |") or die "Couldn't fork: $!";
while (my $line = <CMD>) {
  # read output from command linewise
}

# or slurp the whole output into one string
# {
#   local $/;
#   $string = <CMD>;
# }

# or read the output into an array for easy line access
# my @lines = <CMD>;

close CMD;