Retrieve CPU usage and memory usage of a single process on Linux?

ps command (should not use):

• CPU usage is currently expressed as the percentage of time spent running during the entire lifetime of a process.

top command (should use):

• The task's share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time.

Use top to get CPU usage in real time(current short interval):

top -b -n 2 -d 0.2 -p 6962 | tail -1 | awk '{print $9}'

will echo like: 78.6

• -b: Batch-mode
• -n 2: Number-of-iterations, use 2 because: When you first run it, it has no previous sample to compare to, so these initial values are the percentages since boot.
• -d 0.2: Delay-time(in second, here is 200ms)
• -p 6962: Monitor-PIDs
• tail -1: the last row
• awk '{print $9}': the 9-th column(the cpu usage number)

ps -p <pid> -o %cpu,%mem,cmd

(You can leave off "cmd" but that might be helpful in debugging).

Note that this gives average CPU usage of the process over the time it has been running.

A variant of caf's answer: top -p <pid>

This auto-refreshes the CPU usage so it's good for monitoring.