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

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linuxbasicsforhackers

Common Built-in Bash Commands

A Sample Run
Now we can run our simple scanner script with the variables that determine
what IP address range and port to scan without having to edit the script
every time we want to run a scan:
kali >./MySQLscannerAdvanced.sh
Enter the starting IP address :
192.168.181.0
Enter the last octet of the last address :
255
Enter the port number you want to scan for :
3306
Host: 192.168.181.254 () Ports:3306/open/tcp//mysql//
The script prompts the user for the first IP address, the last octet of the
last IP address, and then the port to scan for. After collecting this info, the
script performs the nmap scan and produces a report of all the IP addresses
in the range that have the specified port open. As you can see, even the
simplest of scripting can create a powerful tool. You’ll learn even more
about scripting in Chapter 17.
Common Built-in Bash Commands
As promised, Table 8-1 gives you a list of some useful commands built
into bash.
Table 8-1:
Built-in Bash Commands
Command
Function
:
Returns 0 or true
.
Executes a shell script
bg
Puts a job in the background
break
Exits the current loop
cd
Changes directory
continue
Resumes the current loop
echo
Displays the command arguments
eval
Evaluates the following expression
exec
Executes the following command without creating a new process,
replacing the current process
exit
Quits the shell
export
Makes a variable or function available to other programs that are
executed from this shell

Bash Scripting
91
Command
Function
fg
Brings a job to the foreground
getopts
Parses arguments to the shell script
jobs
Lists background (bg) jobs
pwd
Displays the current directory
read
Reads a line from standard input
readonly
Declares as variable as read-only
set
Lists all variables
shift
Moves the script's input parameters to the left, dropping the first
parameter (useful for consuming all parameters one at a time)
test
Evaluates arguments
[[
Performs a conditional test
times
Prints the user and system times
trap
Traps a signal so the script can handle it (untrapped signals terminate
the script)
type
Displays how each argument would be interpreted as a command
umask
Changes the default permissions for a new file
unset
Deletes values from a variable or function
wait
Waits for a background process to complete
Summary
Scripting is an essential skill for any hacker or system administrator. It
enables you to automate tasks that would normally take hours of your time,
and once the script is saved, it can be used over and over again. Bash script-
ing is the most basic form of scripting, and you will advance to Python
scripting with even more capabilities in Chapter 17.

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