Quick temporary Wi-Fi AP for Raspberry Pi 4B

myhostapd.conf

interface=wlan0
driver=nl80211
ssid=linksys
hw_mode=a
ieee80211ac=1
channel=149
wmm_enabled=0
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=1234
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
rsn_pairwise=CCMP

wifiap.sh

#!/bin/sh
# There are plenty of guides to configuring a Raspberry Pi as a persistent Wi-Fi
# access point (AP) bridging to wired Ethernet, but I wanted a quick script that
# could set up an AP temporarily.  This way, you can have the Pi default to
# accessing Wi-Fi as a client most of the time, but you can easily set up an AP
# whenever you want without worrying that some time later you'll forget it's in
# AP mode and then have trouble accessing it.
#
# Nothing this script changes is persistent, so when you want to stop AP mode,
# just reboot the Pi.  Alternatively, you could read the man pages and undo
# everything the script does.
#
# This requires the hostapd and bridge-utils utilities, which you can install
# like so:
#   sudo apt install hostapd bridge-utils
#
# The myhostapd.conf file (example included in this gist) should be in the same
# directory as this script (or otherwise findable), and remember to change the
# SSID and password in the configuration file.
echo "Stopping Wi-Fi. . . ."
sudo wpa_cli terminate
sudo ifdown wlan0
echo "Stopping DHCP. . . ."
sudo dhcpcd --release
sudo dhcpcd --exit
echo "Starting hostapd. . . ."
sudo hostapd -B myhostapd.conf
sleep 10s
echo "Setting up bridge. . . ."
sudo brctl addbr br0
sudo brctl addif br0 eth0
sudo brctl addif br0 wlan0
echo "Enabling IP forwarding. . . ."
sudo sysctl -w net.ipv4.ip_forward=1
sudo sysctl -w net.ipv6.conf.all.forwarding=1
echo "Getting IP addresses. . . ."
sudo dhcpcd --master --denyinterfaces=eth0,wlan0 --timeout=10 br0
echo "Done."