check ports opened in docker container of Host mode

checkPorts.sh

#!/bin/sh
# Port Exporter
#
# Description:
#       When docker containers are running in Host mode, thus /proc/[int]/net are shared across all containers.
#       This script mimicks the "netstat -nlp".
#       Firstly it finds all fds in current container into $FDS, then traverses /proc/[int]/net/tcp and /proc/[int]/net/tcp6 to collect fds. If any fd is in $FDS, the port is presumed to be opened in current container.
#

# if SKIP_PORT_CHECK is set, skip port check
if [ "$SKIP_PORT_CHECK" ]; then
	exit 0
fi

# below new line is made deliberately
IFS=$"
"
# stores all port found
PORTS_ARRAY=""

# Finds all PID
PIDS=$(ls /proc | grep -G '^[0-9]*$')
for PID in $PIDS
do
	# Skips non-exist PID by script itself
	FDS=$(ls -al /proc/$PID/fd 2> /dev/null)
	if [ "$?" -ne "0" ]; then
		continue
	fi
	# Parse all FDs
	FDS=$(echo "$FDS" | grep socket | awk -F[ '{ print $2 }' | awk -F] '{ print $1 }')
	contains () {
	for INODE in $FDS
	do
		if [ $INODE -eq $1 ]; then
			# Parse hex port to decimal, append to PORTS_ARRAY
			PORTS_ARRAY="$PORTS_ARRAY\n$((0x$2))"
		fi
	done
	}
		TCP_LINES=$(cat /proc/$PID/net/tcp /proc/$PID/net/tcp6 | grep \ 0A\ )
	for LINE in $TCP_LINES
	do
		INODE=$(echo $LINE | awk '{ print $10 }')
		PORT=$(echo $LINE | awk '{ print $2 }' | awk -F: '{ print $2 }')
		contains $INODE $PORT
	done
done

echo -n $PORTS_ARRAY

FOUND=$(echo $PORTS_ARRAY | grep -e "^$PORT_TO_CHECK$")

# if no port provided and at least one port being found in PORTS_ARRAY
if [ ! "$PORT_TO_CHECK" ] && [ !"$PORTS_ARRAY" ]; then
	exit 0
# $PORT_TO_CHECK found in $PORTS_ARRAY
elif [ "$PORT_TO_CHECK" ] && [ "$FOUND" !=  "" ]; then
	exit 0
else
	exit 1
fi