Linux System Administration

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Appendix: bash Script Samples

Don’t try to execute this command at your terminal and view the

results on the screen. You’ll go blind for 10 minutes and your dog will

start meowing. Did you give in to the temptation to do so? You may

have to execute an stty sane command to restore the screen to a useful

state.

Authoritative DNS Lookup

This script uses the dig command introduced in Chapter 3 to do DNS lookups,

bypassing the cache of the local DNS caching server. One feature of this script is that

it uses its own name to specify what DNS record type to look up. If the script is

named a, it looks up DNS

A records. If it is named soa, it looks up DNS SOA records.

The name ptr is a special case that takes an IPv4 address and converts it to the proper

in-addr.arpa form to do the actual lookup. You should make a copy of this script

with the appropriate name for each of the common DNS record types you may need

to look up: a, aaaa, mx, and so on. You can also use hard links or symlinks to create

the aliases.

Regardless of the name, the script takes a list of hostnames to look up as arguments:

#!/bin/bash

#----------------------------------------------------------------

# Copyright © 2006 - Philip Howard - All rights reserved

#

# script a, aaaa, cname, mx, ns, ptr, soa, txt

#

# purpose Perform direct DNS lookups for authoritative DNS

# data. This lookup bypasses the local DNS cache

# server.

#

# syntax a [ ...