port scanner for bash

pscan

#!/bin/bash

## helpers
dec2ip() {
    local delim ip dec=$@
    for e in {3..0}
        do ip+=${delim}$(((dec>>(8*e))&0xFF)) && delim=.
    done
    printf '%s\n' "$ip"
}

usage() {
    echo "${0} ip[/mask]:port[-port]"
    echo "use cidr notation"
    exit $@
}

## checks and init
# check: exactly one parameter
[ $# == 1 ] || usage 1
# check: parameter format
echo "$1" | egrep -q '^(\d+\.){3}\d+(\/\d+)?:\d+(-\d+)?$' || usage 2

# init: proceed to split
tgt="$1"
cidr=$(echo "${tgt}" | cut -d':' -f1)
port=$(echo "${tgt}:" | cut -d':' -f2)
plo=$(echo "${port}" | cut -d'-' -f1)
phi=$(echo "${port}" | cut -d'-' -f2)
mask=$(echo "${cidr}/" | cut -d'/' -f2)
ip=$(echo "${cidr}/" | cut -d'/' -f1)

eval dip=$(echo "\$(((((((($ip))" | sed 's/\./)<<8\)\+/g')
lower=${dip}
upper=${dip}
if [ ! -z "$mask" ]
then
    bmask=$((2**32-2**(32-mask)))
    lower=$((dip&bmask))
    upper=$(((((1<<32)-1)^bmask)+lower))
fi

for hst in $(seq -f %.0f ${lower} ${upper})
    do hip=$(dec2ip ${hst})
    for ps in $(seq -f %.0f ${plo} ${phi})
        do timeout 1 bash -c "echo >/dev/tcp/${hip}/${ps} && echo \"ip ${hip}:${ps} is open\" || echo \"ip ${hip}:${ps} is closed\"" 
    done
done

default cidr mask to /32

skip calculation when mask empty