Persistent SSH tunnel helper

ssh-tunnel.sh

#!/usr/bin/env bash

# Quit on error
set -e

# Functions
msg() {
    echo -e "\x1B[1m$1\x1B[0m"
}

usage() {
	echo "Usage:"
	echo "  Setup:    $0    -u user -h host -s srcport -d dstport [-H dsthost]"
	echo "  Teardown: $0 -T -u user -h host -s srcport -d dstport [-H dsthost]"
	echo "  Help:     $0 --help"
}

help() {
	echo "Examples:"
	echo
	echo "  Tunnelling localhost:1234 to MySQL on somehost:3306"
	echo "    $0 -u arnold -h somehost -s 1234 -d 3306"
	echo "  After running the above command, you can connect to the MySQL server like so:"
	echo "    mysql -h 127.0.0.1 -P 1234"
	echo "  To close the tunnel afterwards:"
	echo "    $0 -T -u arnold -h somehost -s 1234 -d 3306"
	echo
	echo "  ---"
	echo
	echo "  Tunnelling localhost:1234 to MySQL on farawayhost:3306 THROUGH somehost"
	echo "    $0 -u arnold -h somehost -s 1234 -d 3306 -H farawayhost"
}

# Static value
CONTROL_SOCKET='~/.ssh/%h_%p_%r.multiplex'

# Default values
DSTHOST=localhost
TEARDOWN=false

# Start parsing arguments
if [ "$1" == "--help" ]; then
    usage
    echo
    help
    exit 0
fi

GIVEN=0
OPTIND=1
while getopts ':u:h:s:d:H:T' OPT; do
    case "$OPT" in
        u )  USER="$OPTARG"
             GIVEN=$((GIVEN+1))
             ;;
        h )  HOST="$OPTARG"
             GIVEN=$((GIVEN+1))
             ;;
        s )  SRCPORT="$OPTARG"
             GIVEN=$((GIVEN+1))
             ;;
        d )  DSTPORT="$OPTARG"
             GIVEN=$((GIVEN+1))
             ;;
        H )  DSTHOST="$OPTARG"
             ;;
        T )  TEARDOWN=true
             ;;
        \?)  echo "Unknown option: -$OPTARG" >&2
             usage >&2
             exit 1
             ;;
        : )  echo "Missing option argument for -$OPTARG" >&2
             usage >&2
             exit 1
             ;;
        * )  usage >&2
             exit 1
             ;;
    esac
done

if [ $GIVEN -lt 4 ]; then
    echo "Some mandatory options are missing. Make sure you have provided '-u', '-h', '-s' and '-d'" >&2
    usage >&2
    exit 1
fi

if [ "$TEARDOWN" == "true" ]; then
    echo -n "Closing SSH tunnel ... "
    ssh \
        -o "ControlPath=$CONTROL_SOCKET" \
        -TO "exit" \
        $USER@$HOST
    exit
fi

msg "Opening SSH tunnel $USER@$HOST $SRCPORT => $DSTHOST => $DSTPORT"

# Create SSH tunnel
# Errors will be caught by "set -e"
# -f: Go to background
# -q: Suppress MOTD
# -N: Don't execute any commands (forward only)
# -T: Don't allocate pseudo-terminal
# -M: Use as master process (so we can exit later)
ssh \
    -o ExitOnForwardFailure=yes \
    -o "ControlPath=$CONTROL_SOCKET" \
    -fqNTML "$SRCPORT:$DSTHOST:$DSTPORT" \
    $USER@$HOST