delete_host_from_dns

#!/bin/bash

function usage {
    echo
    echo "Usage: $0 [-k keyfile] [-d] [-nr] [-f] [--dry-run] name"
    echo
    echo "Removes A, AAAA, TXT, and optionally, PTR records for a name from (dynamic) DNS"
    echo
    echo "Options:"
    echo "-k  --keyfile   DNS keyfile, default is $keyfile"
    echo "-nr --noreverse Do not remove PTR (reverse) records"
    echo "-nt --notxt     Do not remove TXT records"
    echo "-f  --force     Force removal, no warnings, no dry-run"
    echo "--dry-run       Just show me what will be done (default on)"
    echo
    exit 0
}

echo -n "Looking for nsupdate ... ";
which nsupdate || exit 1


debug=false
force=false
quiet=false
noreverse=false
dry_run=true
name='(unset)'
reverse6='(unset)'
keyfile=~/.cert/Kmykey.key

while [[ $1 =~ ^- ]]; do
    case $1 in
        "--debug"|"-d")
            debug=true
            ;;
        "--force"|"-f")
            dry_run=false
            ;;
        "--noreverse"|"-nr")
            noreverse=true
            ;;
        "--notxt"|"-nt")
            notxt=true
            ;;
        "--dry-run")
            dry_run=true
            ;;
        "--key-file"|"-k")
            shift
            keyfile=$1
            ;;
        *)
            echo "Unknown option $1"
            echo; usage
            exit 1
            ;;
    esac
    shift
done

name="$1"

if [ "$name" = "" ]; then usage; fi

# First check if name is a cname
cname="$(dig +short CNAME "$name")"
if [ "$cname" = "" ]; then true
else
  echo "$name is a CNAME for $cname"
  echo "I don't do CNAMEs"
  exit 1
fi

tempfile="$(mktemp)"
revtfile="$(mktemp)"

function inforevert {
  echo
  echo "Revert file is $revtfile"
  echo "To revert all changes, try"
  echo "nsupdate -v -k $keyfile < $revtfile"
  echo
  echo "Note: tempfiles are left behind. Clean up after yourself."
  echo "Your mother does not work here."
  echo
}

# Is there anything there?
if [ "$name" = "" ]; then usage; fi
if $debug; then echo "DEBUG: name is $name"; fi

# Find ns. We have to pick one.
ns="$(dig +noall +authority soa $name | awk '{print $5}' | sort -n | head -1)"
if [ "$ns" = "" ]; then
  echo "Unable to find SOA NS nameserver record for $name"
  exit 1
fi
if $debug; then echo "NS is $ns"; fi


# Find A and AAAA records
n=0
if $debug; then echo DEBUG: A, AAAA, and TXT records:; fi
while read rname ttl class type value; do
  if [ "$value" = "" -o "$rname" != "$name." ]; then echo "Warning: No A or AAAA record found"; fi
  if $debug; then echo "  DEBUG: $type record is $value"; fi
  if [ "$type" = "A" -o "$type" = "AAAA" ]; then
    records[$n]="$value"; ((n++));
  fi
  echo "update delete $rname $ttl $class $type $value" >> "$tempfile"
  echo "update add    $rname $ttl $class $type $value" >> "$revtfile"
  echo send   >> $tempfile
  echo send   >> $revtfile
  echo answer >> $tempfile
  echo answer >> $revtfile
done < <(
  dig +noall +answer A $name @$ns
  dig +noall +answer AAAA $name @$ns
  if $notxt; then true
  else
    dig +noall +answer TXT $name @$ns
  fi
)
r=${#records[*]}

if $noreverse; then true
else
  if $debug; then echo "DEBUG: PTR records:"; fi
  # Find PTR record
  if (( r>0 )); then
    n=0
    while read rname ttl class type value; do
        ptrrecords[$n]="$ptr"; ((n++))
        echo "update delete $rname $ttl $class $type $value" >> "$tempfile"
        echo "update add    $rname $ttl $class $type $value" >> "$revtfile"
        echo send   >> $tempfile
        echo send   >> $revtfile
        echo answer >> $tempfile
        echo answer >> $revtfile
        if [ "$value" = "$name." ]; then true
        else
          echo "  Warning: Reverse lookup for $rname $value does not match name $name., SWITCHING DRY-RUN ON" 1>&2
          dry_run=true
        fi
    done < <(
      for i in ${records[*]}; do
      if reverse="$(host $i)"; then
        reverse="$(echo $reverse | cut -d ' ' -f 1)"
        pns="$(dig +noall +authority soa $reverse | awk '{print $5}' | sort -n | head -1)" # have to pick one
        dig +noall +answer PTR $reverse @$pns
      else
        echo "  Warning: No reverse lookup for $i" 1>&2
      fi

      done
    )

  fi
  if $debug; then echo DEBUG: number of ptr records: ${#ptrrecords[*]} 1>&2; fi
fi
p=${#ptrrecords[*]}

if (( (r+p) == 0 )); then
  echo "Found no records to remove"
  exit 0
fi

if $dry_run; then
  echo 
  echo "DRY RUN MODE"
fi
  echo "Will run these commands against DNS:"
  echo
  cat $tempfile
  echo
if $dry_run; then
  echo
  echo "THIS IS DRY RUN MODE"
  echo "To apply these changes for real, do"
  echo "nsupdate -v -k $keyfile < $tempfile"
  echo
  echo "You may remove the tempfile or edit it and run the above command by hand"
else
  echo "Running commands:"
  nsupdate -v -k "$keyfile" < $tempfile

  if [ $? -eq 0 ]; then 
    rm -v "$tempfile"
  else
    echo nsupdate failed, check output
  fi
fi

inforevert