Notes:

Bash 101 Course

 

When performing security assessments, it is very import that you have a repeatable process.  As you become familiar with more tools, you will want to incorporate them into your process.  Bash scripting is an easy way in which this can be accomplished.  Learn how to read, edit and parse critical information that you need from the output of various tools.  Take user's input and leverage multiple tools to perform OSINT.  Starting with the very basics and taking you through functions and nested arrays, you will learn to build out your own pentest framework that works for you.

 

A very import thing to remember when scripting, is that there are many ways to solve a particular problem.  There is no right way.  Whatever works for you, is the best way.

 

Everything you do from the command line can be scripted.

 

Many of the examples in this class are the same types of commands, that when linked together in a script, can create very useful programs.

 

My editors of choice:

     CLI - nano

     GUI - gedit

 

Create a text file:

     touch file Creates an empty file.

     pipe the output of a command

          ifconfig > tmp

     nano file

 

nano

     ctrl v     Next page.

     ctrl y     Previous page.

     ctrl w    Where is (find).

     ctrl k     Cut that line of test.

     ctrl x     Exit editor.

 

Create a file and append text to it:

     ifconfig > tmp     

     echo >> tmp

     ping google.com -c3 >> tmp

 

How to view a file:

     cat file Show entire contents of file.

     more file Show one page at a time.  Space bar for next page and (q) to exit.

     head file Show the first 10 lines.

     head -15 file Show the first 15 lines.

     tail file Show the last 10 lines.

     tail -15 file Show the last 15 lines.

     tail -f file Useful when viewing the output of a log file.

 

pipe

     Feeds the output of one process to the input of another process.

     cat tmp | grep Bcast

 

Processes

     ps aux Show all running process for all users.

     kill -9 PID Nicely kill a PID.

 

Example

     tab 1 ping google.com

     tab 2 ps aux | grep ping

kill -9 (ping PID)

     tab 1 Verify that ping has stopped.

 

Example

     tab 1 ping google.com > tmp2

     tab 2 tail -f tmp2

     tab 1 ctrl z (pauses the process), bg to background the process.

     tab 2 You can still see the log growing.

     tab 1 fg to foreground the process.

ctrl c to kill the process.

     tab 2 Verify the log file has stopped growing.

ctrl c to kill the process.

 

Count the number of lines in a file:

     wc -l tmp2

 

cut

     -d  delimiter

     -f  fields

 

sort

     sort -u file Sort by unique.

 

Problem

     Isolate the IP address

     cat tmp2 | cut -d '(' -f2 | cut -d ')' -f1 | sort -u

 

awk

     awk '{print $1}' file Show the 1st column.

     awk '{print $1,$5}' file Show the 1st and 5th columns.

     

Problem

     Show the 5 shortest and longest response times to a domain.

     

grep

     grep -v Remove a single string. grep -v 'red' file

     egrep -v Remove multiple strings. egrep -v '(red|white|blue)' file

 

sed

     sed 's/FOO/BAR/g' file Replace FOO with BAR.

     sed 's/FOO//g' file Replace FOO with nothing.

     sed '/^FOO/d' file Remove lines that start with FOO.

 

color

     31=red 32=green 33=yellow 34=blue 35=magenta 36=cyan 

     echo -e "\e[1;34mThis is a blue text.\e[0m"

 

Your first bash script.

     #!/bin/bash

     clear

     echo

     echo

     print "Hello world."

 

Make a file executable.

     chmod +x file

     chmod 755 file

 

Variables

     name=Lee

     echo $name

 

     user=$(whoami)

     echo $user

 

     echo 'Hello' $name. 'You are running as' $user.

 

Problem

     Hello <your name>. Your IP address is <your IP>.

 

Problem

     Name  <your name>

     IP  <your IP>

     Interface  <your interface>

     

User Input

     read -p "Domain: " domain

 

Check For No User Input

     if [ -z $domain ]; then

          echo

          echo "#########################"

          echo

          echo "Invalid choice."

          echo

          exit

     fi

To see more of what you can do with bash scripting, please visit my collection of bash scripts and pentesting framework:
https://github.com/leebaird/backtrack-scripts