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check out uptime. Sample output:

   11:34:56 up 9 days,  3:24,  5 users,  load average: 3.08, 4.04, 14.66

and since I'm sure you forgot: load is “processes waiting for cpu time to execute”, the 3 numbers are “in the last minute”, “in the last 5 minutes”, and “in the last 15 minutes”. (i think). theoretically, if that number is less than the number of cores that you have, you have resources to spare for more.

anyway, let's get one of those numbers. Here's the regular expression one would expect:

^.*load average: (([\d\.]){3,}).*$

Here's (uptime piped to) the sed command:

uptime | sed 's/^.*load average: \(\([0-9.]\)\{3,\}\).*$/\1/'

• escape the parenthesis.
• escape the brackets.
• there is no \d.
• don't escape the dot, to literally match .
• escape the braces.
• Now, outside of the brackets, don't escape the dot to match the wildcard character. You'll notice that not escaping the dot now does the opposite.
• capture group 1 is not $1, it's \1.