Accept IP-address on SSH port for a timeout interval

acceptsship.sh

#!/bin/sh

DEFAULT_TIMEOUT=60
ACCEPTSCRIPT=$0

if [ "$1" = "" ]; then
    echo
    echo "Usage:"
    echo "       acceptsship.sh <ip-address> [timeout=${DEFAULT_TIMEOUT}s]"
    echo
    exit 1
fi

IPADDR=$1
TIMEOUT=$2

# check validity of IP-Address
IP_REGEX='^\(\([0-9]\|[1-9][0-9]\|1[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)\.\)\{3\}\([0-9]\|[1-9][0-9]\|1[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)$'
IPADDR_CHECK=$(echo $IPADDR | sed s/$IP_REGEX//)
if [ "$IPADDR_CHECK" = "$IPADDR" ]; then
    echo "Invalid IP-Address!"
    exit 1
fi

# check validity of timeout
if [ "$TIMEOUT" = "" ]; then
    TIMEOUT=$DEFAULT_TIMEOUT
fi
if [ "$TIMEOUT" -gt "300" ]; then
    TIMEOUT=$DEFAULT_TIMEOUT
fi
if [ "$TIMEOUT" -le "0" ]; then
    TIMEOUT=$DEFAULT_TIMEOUT
fi

TIMEOUT_CHECK=$(expr $TIMEOUT + 0)
if [ $? != 0 -o "$TIMEOUT_CHECK" != "$TIMEOUT" ]; then
    echo "Timeout must be a numeric value!"
    exit 1
fi

# check if the script is already running
pidof -o %PPID -x $ACCEPTSCRIPT > /dev/null
if [ $? != 1 ]; then
    echo "Already running!"
    exit 1
fi

echo "Accepting SSH connections from $IPADDR for $TIMEOUT seconds..."

acceptaddress()
{
    iptables -I INPUT -s $IPADDR -p tcp -m tcp --dport 22 -j ACCEPT && \
    sleep $TIMEOUT && \
    iptables -D INPUT -s $IPADDR -p tcp -m tcp --dport 22 -j ACCEPT
}

acceptaddress &

# close standard output and exit
>&-
exit 0