Use special characters as variables in bash

I have often run into problems where I needed to use a special character, such as a tab with grep in bash, and was unable to pass the tab as "\t".  I had to define a variable as the tab character using the octal value of the tabcharacter.

For instance, to grep for "foo(tab)bar" I had to do the following:

tabChar=`echo -e '\011'`
grep "foo${tabChar}bar" < input

Here is a list of the octal values of a few special characters that may be handy.

OCTAL	ESC'D	CTRL	DESCRIPTION
007	\a	Ctrl-G	Alert/Beep
010	\b	Ctrl-H	Backspace
011	\t	Ctrl-I	Horizontal Tab
012	\n	Ctrl-J	Newline (line feed)
013	\v	Ctrl-K	Vertical Tab
014	\f	Ctrl-L	Form Feed (clear terminal)
015	\r	Ctrl-M	Carriage Return
033	\e	Ctrl-[	Escape
047	\'		Single Quote
134	\\		Backsplash

I hope this list helps.

Compile list of IPs & PTR Records from list of IP Addresses

Simple bash script to compile a list of IP Addresses and corresponding PTR Records from a list of IP Addresses.  Make sure to give this file executable permissions (chmod +x filename).  This script will read the input file, use dig to lookup ptr records, and will output a list of the ptr records and ip address.

#!/bin/bash

inFile="input_list"

outFile="output_list"

ht=`echo -e '\011'`   # tab character

for ip in `cat $inFile`

   do

   in_addr=`echo $ip | awk -F'.' -vOSF='.' '{ print $4"."$3"."$2"."$1".in-addr.arpa" }'`   ptr=`dig PTR $in_addr | grep "IN${ht}PTR" | grep -v ';' | awk -F"$ht" -vOSF="$ht" '{ print $3 }' | sed 's/\(.*\)./\1/'`

   echo "$ptr  $ip" >> $outFile

done