Flushes the DNS cache in all recent versions of OSX. I'm not a Bash guy so this is probably sloppy.

flushdns.sh

# Adapted from the following post:
# How to Flush DNS Cache in Mac OS X
# http://osxdaily.com/2008/03/21/how-to-flush-your-dns-cache-in-mac-os-x/

if [[ $EUID -ne 0 ]]; then
    echo "This script must be run as root." 1>&2
    exit 1
fi

OSVERSION=$(sw_vers -productVersion)

case "$OSVERSION" in
    10.11.*|10.9.*)
        echo "On $OSVERSION (dscacheutil -flushcache + killall -HUP mDNSResponder)"
        dscacheutil -flushcache
        killall -HUP mDNSResponder
        ;;
    10.10.*)
        echo "On $OSVERSION (discoveryutil mdnsflushcache + udnsflushcaches)"
        discoveryutil mdnsflushcache
        discoveryutil udnsflushcaches
        ;;
    10.7.*|10.8.*)
        echo "On $OSVERSION (killall -HUP mDNSResponder)"
        killall -HUP mDNSResponder
        ;;
    10.5.*|10.6.*)
        echo "On $OSVERSION (dscacheutil -flushcache)"
        dscacheutil -flushcache
        ;;
    10.4.*|10.3.*)
        echo "On $OSVERSION (lookupd -flushcache)"
        lookupd -flushcache
        ;;
esac