Implementing netcat in bash

nc_on_bash.sh

#!/bin/bash

SERVER_ADDR=$1
SERVER_PORT=$2

_command_exists() {
        type "${1}" &> /dev/null
}

_nc() {
        (echo >/dev/tcp/${1}/${2}) >/dev/null 2>&1
}

NC_ON_BASH=0
if _command_exists nc ; then
        NC_BIN=$(which nc)
else
        if _command_exists ncat ; then
                NC_BIN=$(which ncat)
        else
                NC_ON_BASH=1
        fi
fi

if [[ ${NC_ON_BASH} -eq 1 ]]; then
        _nc "${SERVER_ADDR}" "${SERVER_PORT}"
else
        ${NC_BIN} -z "${SERVER_ADDR}" "${SERVER_PORT}" $@ >/dev/null 2>&1
fi
if [ $? -eq 0 ]; then
        echo "Connected"
else
        echo "Error: ${SERVER_ADDR}:${SERVER_PORT} not listen."
fi