I was recently solving a CTF challenge that I found quite strange, first of all I have been given a chain of characters that no matter how hard I try to find an answer I can not find it, I am going to publish part of that chain in order to have an answer that can guide me and not sabotage the challenge:


The first thing I thought is that it can not be a type of hash, I've never seen anything like that, so after looking for clues I found a possible answer and put this string in the Command prompt, and this was the result:

root@localhost:~/Folder# (here goes the chain)

It's like when you put "python" and it allows you to continue writing sentences in the language, after that I tried to paste other blocks of the chain and I received messages like this:

bash: (chain): event not found
bash: command substitution:

Is it possible that it is a coded bash statement and if so, how can I decode it or understand it? If it is not what I think then exactly?

I hope you can guide me

1 Answer 1


I don't know what that chain of characters is, but it's clearly not a shell command. What's happening is that bash is trying to interpret and act on various shell metacharacters in the string, but they're used in ways that don't make any sense, so bash is getting errors and/or doing things that don't make any sense.

Specifically: the string you linked starts with "D" followed by a single-quote. When bash sees a single-quote, it treats it as the beginning of a quoted section of the command line. There's no second single-quote to mark the end of the quoted section, so when you press return after entering it, the shell thinks you're entering a multi-line string. The "> " prompt is bash's standard continuation prompt, which indicates that you haven't entered a complete command yet, and you need to keep going until you get to a valid stopping point (i.e. not in the middle of a quoted string).

The other messages you report have to do with other metacharacters in the blocks of your chain:

  • bash treats "!" as the start of a history substitution, i.e. reusing all or part of a previous (historic) command (a past "event"); what comes after the "!" indicates what "event" you want to reuse, but it doesn't match anything so you get an "event not found" message.

  • bash treats backquotes as indicating command substitutions, i.e. running what's in backquotes as a command, then substituting that command's output in the current command line. I don't know exactly what the relevant text or error is, but apparently there's something that doesn't make sense between a couple of backquotes, and so the shell is complaining about it.

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