Explanation of a script

Issue

General description
I don’t understand the next script; the general idea is the script takes stdout and
writes down a file encoded(or shifted characters).

tr 'A-Za-z' 'N-ZA-Mn-za-m' <<EOF | bash -
  #!/ova/onfu
  ge '!-~' 'C-~!-B' < f-04-erfhygnqbf-rap.fu | onfu -
EOF

The first line seems to shifht characters based on two sets:

'A-Za-z'

and

'N-ZA-Mn-za-m' 

in some (random?) order. Then pipe it to bash.
Then it is defined a path

  #!/ova/onfu 

but there isnt this path in the system nor interpreter, then whats the use?
next

  ge '!-~' 'C-~!-B' < f-04-erfhygnqbf-rap.fu | onfu - 

ge ,I understand, is an option meaning greather than, but

'!-~' 'C-~!-B' 

how can be greather than a character (using the utf8 code?, I mean their
hex values?)

this is taken of

f-04-erfhygnqbf-rap.fu

(is this a temporary file?). But then this is piped to onfu.

This scripts output a file with a whole mess of characters.

Questions
The general question: is what is this script doing?

As interesting points, I’d say :

• How does it work tr here?
• How does it work <<EOF?
• What is /ova/onfu?
• How does function the ge comparation?
• This script seems to reencode a stdout output, how can it be recovered?

Thanks.

Solution

The tr command is translating every letter to the letter 13 places ahead in the alphabet, wrapping around at Z. This is the ROT13 encoding.

The output of this is then piped to bash, so it will execute it as a shell script.

<<EOF indicates that the input to tr is a here-doc. It passes all the lines until the EOF line as the input.

If you want to see the decoded script without executing it, get rid of | bash and it will be printed on the screen.

Answered By – Barmar

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