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Table of contents
  1. History
  2. Diff
  3. Here Documents
  4. Named Pipes with mkfifo
  5. Scan host for open ports w/ nmap
  6. Devices /dev
    1. Mounting devices
    2. Getting information on mounted drives
    3. Permanently deleting files with shred
  7. Masking your IP for web scraping
  8. Running Scripts At System Startup

History

  • See history with history command
  • You will get a number for each history item.
  • You can replay any number n with command !n
  • History on OS X is stored in ~/.zsh_history

!n refer to command number n in history when you call history

Diff

You can difff two files, you usually want to see a unified diff b/c that is easier to read

diff -u file1.txt file2.txt

Here Documents

Instead of using echo, our script now uses cat and a here document. The string EOF (meaning end of file, a common convention) was selected as the token and marks the end of the embedded text. Note that the token must appear alone and that there must not be trailing spaces on the line.

Unlike Echo, all double quotes and single quotes are escaped. Here is an example of the same thing at the command line.

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[me@linuxbox ~]$ foo="some text"
[me@linuxbox ~]$ cat << _EOF_
> $foo
> "$foo"
> '$foo'
> \$foo
> _EOF_ 
some text 
"some text" 
'some text' 
$foo

Named Pipes with mkfifo

Named pipes are input/output buffers. You can fill up the buffer and then drain the buffer later.

  1. Setup Named Pipe using mkfifo

  2. Fill up the named pipe, this will hang until the pipe is drained

Hamel: you can run this part in a sub shell

  1. In a NEW terminal window drain the pipe

Hamel: put it all together in a script. You can drain the pipe as many times as you want.

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#!/bin/bash

mkfifo pipe1
ls -l > pipe1 &
cat < pipe1

Scan host for open ports w/ nmap

  1. Lookup ip with nslookup
  2. nmap -sT <IP address>

You can scan a range of IPs for a mysql port like so:

nmap -sT 192.168.181.0/24 -p 3306 -oG MySQLScan

This is useful if you have a public server and you want to verify that a port is open.

Devices /dev

Linux has a special directory that contains files representing attached devices. Important ones are sda1, sda2 , sda3, sdb and sdb1

You can view a tree of your disks and the partitions with the utility lsblk

Mounting devices

Sometimes you need to mount these devices. Two common mount points are /mnt and /media. If you mount the device into an existing directory it will cover the contents of that directory making them invisible and unavailable.

Ex: mount device to /mnt

mount /dev/sb1 /mnt

Ex: mount flash drive

mount /dev/sdc1 /media

You can unmount a device with unmount:

unmount /dev/sb1

Getting information on mounted drives

df -h

Permanently deleting files with shred

This utility writes over files many times in order to erase things. Helpful for sensitive data.

Masking your IP for web scraping

Look into proxy chains

Linux utility called proxychains which generally works as:

proxychains <the command you want proxied> <arguments>

proxychains defaults to using Tor if you don’t supply your own proxies.

See: https://www.technocrazed.com/how-to-use-beagle-scraper-safely-to-scrape-e-commerce-platforms

Running Scripts At System Startup

Look at rc scripts. After the kernel has initialized all its modules, it starts adaemon known as init or initd, which runs scripts found in /etc/init.d/rc

You can use the utility update-rc.d to add a script to the startup procedure:

This is useful if for example you always want to start a database on system startup.