It's the birthday of your friend, and you want to give him a gift. It's a hard mission, because he simply have everything you can imagine...

Why not give to him something special and original?

For example, you could give to him a collection of great musics, photos/videos/slideshow of your best moments ,a private key of a wallet with money you just created for him or any file you want.

You may asking for yourself: What's the deal?

I've been thinking about easter eggs with a toy inside. But not a real easter egg. A virtual easter egg.

I mean files inside of a file like a .zip does.

But what I'll teach here is not how to "zip" files.

It's about hacking a file (in a good cause).

In this tutorial I will teach you how to deal with cat.

No! Not this cat, but a Linux command. By the way, this is my friend, mr. Espeto.

According to Linux man , cat do the following:

"Concatenate files and print on the standard output"

But he will use this in a different way. We will use to write bytes of a file in the end of another one.

What you will need:

• Linux
• Pendrive
• Creativity

^{_{[email protected] Larry Ewing and The GIMP [Attribution or CC0], via Wikimedia Commons}}

Let's go then:

1. Create a folder(directory) inside your home folder. We can name it "stuff" for example.
2. Open a terminal and cd (change directory) to this directory you just created.
   cd /home/username/stuff/
3. Copy all the files you want to give to your friend inside this directory.
4. Select all your files and create a zip file. You can use the right mouse button for this.
5. Open Libre Office Writter and create a pdf. (This pdf will be the container of the zip. The pdf is the easter egg and the zip the toy.)
6. Let's paste bytes of zip into the end of pdf file. (Don't forget to backup before doing this)
   cat files.zip >> happy_birthday.pdf
7. Now the files.zip and the pdf are one single large pdf.
8. Open the pdf to see if this works. (Don't try edit this pdf, because you can mess the already messed file. : -) )
9. Let's test the extraction of the files.zip from the pdf. The first thing you need to know is the size in bytes of files.zip
   du -b files.zip
10. Use this bytes size information (NUMBER) you got with du -b files.zip in the following command
    tail -c NUMBER files.zip > new_files.zip
11. The new_files.zip is created. Open it and test it.

Video

_{* Watch this video in fullscreen mode}

https://youtu.be/r98zGRTT7yc

Important

Don't forget to put the instructions in the pdf about how to catch a cat by the tail command! 😊

^{_{Image Source}}

FAQ

• Can I use these commands in another operating system?
  Sure! You can use it in Windows using the Mingw or Mac, the same command but the parameters may vary. I suggest you to use Linux in a Virtual Machine or boot it liveCD(you don't need to install).
• Is it dangerous to open a file like this?
  No. Since the Adobe Reader and other softwares avoid execution of binary data, this will result in nothing.

SUGGESTIONS

• You can give a high capacity pendrive with this file inside.
  
  ^{_{By Ranjithsiji (Own work) [GFDL or CC BY-SA 3.0], via Wikimedia Commons}}

• You can upload this to any serve that support the file format you are using and share the link. Ex.: Google Docs, Dropbox, etc...
  
  ^{_{Image Souce}}

• You can make a pps slideshow instead of pdf, why not?
  
  ^{_{FOTO:FORTEPAN / MHSZ [CC BY-SA 3.0], undefined}}

• You can make a game "search for the clues".
  
  ^{_{By Penarc (Own work) [GFDL or CC BY-SA 3.0], via Wikimedia Commons}}

• You can make a Geek box with pendrive and candies.
  
  ^{_{Image Source}}

• You can make a good use of a 3D printer and make a weird case for a pendrive or mini cd
  
  ^{_{Por Bradina [CC0], undefined}}

• You can make a program in basic language and save it into a rom to run in ancient computers with z-80(zilog) based architecture, that is possible with the use of a... Eh... Please forget this one.
  
  ^{_{© Nevit Dilmen [CC BY-SA 3.0 undefined GFDL], undefined}}
  

  That's it! Thank you for reading!

  
  ^{_{Image Source - Giphy}}