How to count the number of interfaces in a bridge

Question

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
 }

Answer 1

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/$bridge/brif/*(DN:t))
printf '%s\n' "$#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/$brige/brif/"*)
printf '%s\n' "${#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.