The run function is sufficiently powerful that it may be tempting to rely exclusively on parsing output to get information about the system -- but this has the decided disadvantage that it leaves scripts parsing human-readable output that may or may not change in the future. To more robustly gather information about the system, use the built-in "get" function. In the case of the boot_time property, this will return not the string but rather the ECMAScript Date object, allowing the property value to be manipulated programmatically.
script run('configuration version'); now = new Date(); uptime = (now.valueOf() - get('boot_time').valueOf()) / 1000; printf('up %d day%s, %d hour%s, %d minute%s, %d second%s\n', d = uptime / 86400, d < 1 || d >= 2 ? 's' : '', h = (uptime / 3600) % 24, h < 1 || h >= 2 ? 's': '', m = (uptime / 60) % 60, m < 1 || m >= 2 ? 's': '', s = uptime % 60, s < 1 || s >= 2 ? 's': '');
% ssh root@dory < uptime.aksh Pseudo-terminal will not be allocated because stdin is not a terminal. Password: up 2 days, 10 hours, 47 minutes, 48 seconds
The message about pseudo-terminal allocation is due to the ssh client; the issue that this message refers to can be dealt with by specifying the "-T" option to ssh.