L in u X ba sics for h acke rs g e t t I n g s t a r t e d w I t h

2
T E X T M A N I P U L AT I O N
In Linux, nearly everything you deal with 
directly is a file, and most often these will 
be text files; for instance, all configuration 
files in Linux are text files. So to reconfigure 
an application, you simply open the configuration 
file, change the text, save the file, and then restart 
the application—your reconfiguration is complete.
With so many text files, manipulating text becomes crucial in manag-
ing Linux and Linux applications. In this chapter, you’ll use several com-
mands and techniques for manipulating text in Linux.
For illustrative purposes, I’ll use files from the world’s best network 
intrusion detection system (NIDS), Snort, which was first developed by 
Marty Roesch and is now owned by Cisco. NIDSs are commonly used to 
detect intrusions by hackers, so if you want to be a successful hacker, you 
must be familiar with the ways NIDSs can deter attacks and the ways you 
can abuse them to avoid detection.

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20
Chapter 2
N O T E
 
If the version of Kali Linux you’re using doesn’t come preinstalled with Snort, you 
can download the files from the Kali repository by entering 
apt-get install snort
.
Viewing Files
As demonstrated in Chapter 1, the most basic text display command is 
probably 
cat
, but it has its limitations. Use 
cat
to display the Snort config 
file (snort.conf ) found in/etc/snort (see Listing 2-1).
kali >cat /etc/snort/snort.conf
Listing 2-1: Displaying snort.conf in the terminal window
Your screen should now display the entire snort.conf file, which will 
stream until it comes to the end of the file, and should look something like 
the following code. This isn’t the most convenient or practical way to view 
and work with this file.
#-------------------------------------------------
# VRT Rule Packages Snort.conf
#
# For more information visit us at:
# HYPERLINK “http://www.snort.org/” http://www.snort.org Snort Website
--snip--
# event thresholding or suppressions commands...
kali >
In the following two sections, I will show you the 
head
and 
tail
com-
mands, which are two methods for displaying just part of a file’s content 
in order to more easily view the key content.