how to find all host in network

marek ~ $ nmap -sP 10.91.15.1/24

Starting Nmap 6.46 ( http://nmap.org ) at 2015-03-30 09:20 CEST

Nmap scan report for 10.91.15.1
Host is up (0.064s latency).

Nmap scan report for 10.91.15.2
Host is up (0.24s latency).

Nmap scan report for 10.91.15.3
Host is up (0.26s latency).

Nmap scan report for 10.91.15.59
Host is up (0.041s latency).

Nmap scan report for 10.91.15.61
Host is up (0.31s latency).

Nmap scan report for 10.91.15.234
Host is up (0.00045s latency).

Nmap done: 256 IP addresses (6 hosts up) scanned in 7.67 seconds

alternative:

for i in `nmap -sP 10.91.15.1/24 | grep 10. | awk '{print $5}'`; do ping -c1 $i;done