How to find all devices (IP Address, Hostname, MAC Address) on local network?
If using a third-party utility is not an issue for you, then I recommend giving these a try:

arp-scan (available via Homebrew)

brew install arp-scan
arp-scan --localnet


fing (download and install the "Desktop Embedded CLI" package from fing.com or via Homebrew brew cask install fing)

sudo fing -r 1 -d true -o table,text


Both utilities have a number of additional modes and features. I suggest reading the manuals fully to get the most out of them.

If you need to avoid using third-party tools then here's a way to do something similar with built-in commands. You can run these interactively, but it's probably easier to save it as a script. N.B. to keep it short, this script does no error checking, and only works on /24 subnets. Modifying it to work on subnets of other sizes is left as an exercise to the reader :)

#!/usr/bin/env bash
tab=$'\t'
pIF=$(echo "show State:/Network/Global/IPv4" | scutil | awk -F: '/PrimaryInterface/{sub(/ /,"",$2); print $2}')
sn=$(ipconfig getifaddr $pIF | sed -En 's/^([0-9]+\.[0-9]+\.[0-9]+).*/\1/p')
for i in {1..254}; do ping -i0.1 -W100 -c1 $sn.$i | grep from; done
arp -a | grep $pIF | sed -e 's/^\?/unnamed/' -e "s/\ at\ /${tab}/g" -e "s/\ on\ /${tab}/g" -e 's/\ ifscope.*$//g' | awk 'BEGIN { FS="\t"; OFS="\t"; printf "%-17s\t%-15s\t%s\n", "MAC","INTERFACE","HOSTNAME (IP)" } { if($2!="(incomplete)") {printf "%-17s\t%-15s\t%s\n",$2,$3,$1}}'


This should output something like:

MAC                 INTERFACE       HOSTNAME (IP)
0:90:b:7a:85:62     en0             r1.lan (192.168.20.1)
2c:36:f8:48:2b:47   en0             cisco-sg300-10p.lan (192.168.20.2)
84:78:ac:a6:95:a0   en0             cisco-sg300-20.lan (192.168.20.3)
b4:fb:e4:cb:93:85   en0             wap1.lan (192.168.20.10)
0:11:32:10:cd:c1    en0             nas.lan (192.168.20.20)
0:11:32:3d:99:c9    en0             nas2.lan (192.168.20.21)
0:11:32:10:cd:c1    en0             unnamed (192.168.20.23)
d4:4b:5e:fe:6a:75   en0             brwd44b5efe6a75.lan (192.168.20.90)