If you want to quickly ping every address on a local network to see which are up machines:
```bash
localnet=0                                                   # e.g. 1 if your ips are 192.168.1.x
for s in $(seq 1 254); do 
  ( 
    # -w1 means 1 second deadline
    # -c1 means only one ping
    ping -w1 -c1 "192.168.$localnet.$s" 2>&1 >| "$s"
  )&    # & so pings are run in parallel
done
```
The `&` means all the pings will run in parallel. Do this in an empty directory in `/tmp`,
e.g. `/tmp/x12`, then you will have a bunch of files. Then up machines reply, so you can
```
grep from *
```
whereupon you get
```
1:64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=17.2 ms
2:64 bytes from 192.168.1.2: icmp_seq=1 ttl=64 time=257 ms
31:64 bytes from 192.168.1.31: icmp_seq=1 ttl=64 time=0.048 ms
37:64 bytes from 192.168.1.37: icmp_seq=1 ttl=64 time=942 ms
83:64 bytes from 192.168.1.83: icmp_seq=1 ttl=64 time=406 ms
```
which gives you the ip addresses of up machines on your LAN.

## My current script
```bash
#!/bin/bash
localnet="${localnet-1}" 
for s in $(seq 1 254); do 
  ( 
    # -w1 means 1 second deadline
    # -c1 means only one ping
    ping -w1 -c1 "192.168.$localnet.$s" # 2>&1 >| "$s"
  )&    # & so pings are run in parallel
done
```
so that I can do
```
massping 2>&1 | grep from
```