Shell Programming and Scripting

#!/bin/bash
# Update NETS as needed
#
NETS="00.000.000"
echo
echo "STATE   ADDRESS -------> NAME -------------------> ADDRESS"
echo '-------------------------------------------------------------------'
for NET in $NETS; do
  for n in $(seq 1 254); do
    A=${NET}.${n}                    # builds the range of the subnet
    HOST=$(dig -x $A +short)         # reverse lookup
    if test -n "$HOST"; then         # If string has nonzero length then continue

      for MULTI in `dig +short  -x $HOST`; do
      ADDR=$(dig $HOST +short)       # Now do forward lookup
 done
      if test "$A" = "$ADDR"; then   # if host = IP, then mark it as OK
        echo -e "ok\t$A -> $HOST -> $ADDR"
      elif test -n "$ADDR"; then
        echo -e "fail\t$A -> $HOST -> $ADDR"
      else
        echo -e "fail\t$A -> $HOST -> [unassigned]"
      fi
    fi
  done
done
echo DONE
exit 0

# for safety turn off globbing (wild card matching in current directory)
set -f
...
    MHOST=$(dig -x "$A" +short)      # reverse lookup
    if test -n "$MHOST"; then        # If string has nonzero length then continue

      for HOST in $MHOST; do
            MADDR=$(dig "$HOST" +short)       # Now do forward lookup
            for ADDR in $MADDR; do
...

...
    dig -x "$A" +short |               # reverse lookup
    while read HOST; do
          dig "$HOST" +short |         # Now do forward lookup
          while read ADDR; do
...