For this case, we use batch mode in top. From top's manpage:
Starts top in 'Batch mode', which could be useful for sending output from top to other programs or to a file. In this mode, top will not accept input and runs until the iterations limit you've set with the '-n' command-line option or until killed.
To use it is very easy, you must provide -b for batch mode, and -n for number of iteration that you desire. You can pipe it to less, tail, head or pipe it to a file, according to your need.
foo@thorium:~$ top -b -n 1 | head top - 10:47:15 up 3 days, 23:52, 1 user, load average: 2.01, 0.99, 0.57 Tasks: 140 total, 2 running, 136 sleeping, 0 stopped, 2 zombie Cpu(s): 13.2%us, 4.9%sy, 0.0%ni, 81.6%id, 0.3%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 1025608k total, 865376k used, 160232k free, 80332k buffers Swap: 522236k total, 66468k used, 455768k free, 273996k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1192 root 20 0 122m 65m 10m R 13.8 6.6 559:31.01 Xorg 19333 foo 20 0 234m 61m 13m S 9.8 6.2 626:59.69 nxplayer.bin 19440 foo 20 0 175m 14m 9612 S 7.9 1.5 0:44.78 lxterminal
The above command will list 10 lines of top output in batch mode, and being set to iterate only once.