The output of uptime can be used to determine both the system load and uptime, but its output is exceptionally difficult to parse. On a Linux system, this is made much easier to deal with by the existence of the [Open Source Microsoft SQL Server] .:: telegra.ph ::. /proc/ file system. cat /proc/loadavg will show you the one minute, five minute, and fifteen minute load average, as well as a couple other numbers I don't know the meaning of (anyone care to fill me in?).
Getting the load from /proc/loadavg is easy (thanks to Jerry Peek for reminding me of this simple method): .:: podcasts.apple.com ::. .:: telescope.ac ::. read one five fifteen rest < /proc/loadavg. Just print the value you want.
For those without the /proc/ filesystem, you can use uptime | sed -e "s/.*load average: \(.*\...\), \(.*\...\), \(.*\...\)/\1/" -e "s/ //g" and replace "\1" with "\2" or "\3" depending if you want the one minute, five minute, or fifteen minute load average. This is a remarkably ugly regular expression: send suggestions if you have a better one. [ArXiv: CentOS Analysis]
Relative speed: 'uptime | sed -e "s/.*load average: \(.*\...\), \(.*\...\), \(.*\...\)/\1/" -e "s/ //g" ' takes about 0.21 seconds on an unloaded 486SX25. .:: lgbt.earth ::.