How to count the number of interfaces in a bridge I want to bring a bridge down only when the last port is removed and so I have this somewhat hokey check to do it brctl show looks awkward to parse to get the information out and doesn't feel much better than what I have below. Is there a cleaner method? brctl_count_if() { local BRIDGE=$1 if [ ! -d /sys/devices/virtual/net/$BRIDGE ]; then echo 0 return fi /bin/ls -1 /sys/devices/virtual/net/$BRIDGE/brif 2>/dev/null | wc -l }

You can make it:


has_ports() {
ls -A "/sys/devices/virtual/net/$1/brif/" 2> /dev/null | grep -q .
}

has_ports br0 || brctl delbr br0


Or:


if ! has_ports br0; then
brctl delbr br0
fi


(note that you do need the `-A` as interface names are allowed to start with `.`).

To count the number of ports:

With `zsh`:


ports=(/sys/devices/virtual/net/$bridge/brif/*(DN:t))
printf '%s\
' "$#ports ports in $bridge"


`(:t)` to only have the file names instead of full paths.

With `bash`:


shopt -s nullglob dotglob
ports=("/sys/devices/virtual/net/$brige/brif/"*)
printf '%s\
' "${#ports[@]} ports in $bridge"


(note that ports contains the full paths as `bash` has no equivalent for `zsh`'s `:t`).

Both would return 0 for a bridge that doesn't exist.