Bash Interview: echo

Interviews are funny. You have only very little time to find out whether participating sides are a good match or not. On many different levels: from personal to technical. Traditionally it is established by series of questions and answers (ideally not one sided…).

Good questions are not necessarily about correct answer but they will let you see someone’s thought process, will allow for a conversation about it, and also will enable you to estimate candidate’s experience level. (So the information gained from the interaction is not just binary.) Bonus points if the question will show the candidate that you are a cool place to be.

For example, interviewing someone for a position that involves Linux, I like to ask:

Using echo, print -e (minus e) on a line.

Candidate would be ideally provided with a terminal to play with. Actually, try it yourself before reading any further, it is quite fun (if you are into that kind of thing ;-)).

echo -e

Lol. But no. Hopefully they are just trolling. (I consider being confident enough to make a joke a good sign.)

echo -e -e

Nice try, candidate started to think, but no.

echo -- -e

Okay, candidate knows about -- convention, but no.

\echo -- -e
...

Trying some of previous variants with executable echo rather than builtin one, but no.

echo "-e"
echo '-e'
echo \-e
echo \\-e

Candidate started to panic, interviewer needs to calm them down.

echo -n -; echo e
printf -- '-e\n'
cat <<< -e
echo –e

Fair enough, it is important skill to be able to realize that one is being tricked (and try to trick in response). Interviewer needs to re-assure the candidate that it is indeed possible, with single echo. And that they meant ASCII character -.

echo $'\x2De'

Candidate realized that they need to be sneaky somehow, but still no. Somewhat impressive though as not everyone knows $''.

Hopefully from there it is not far to get to the following.

echo -e '\x2De'

If candidate on top of getting to the correct answer have a big grin on their face (signifying they had fun), I’m happy.

Alternatives/similar

You run echo * yet nothing gets printed. Can you explain?

Hint: directory is not empy. Hidden files are irrelevant.

There is a directory called ~ in current directory. Remove it and all it contains.

Hint: maybe don’t give them terminal to try this one.

Or slightly more obvious version:

There is a file called file; rm -rf ~ in current directory. Remove it.

Also fun thing to ponder:

touch '\e[31mhello'
touch '\e[33mworld'
touch ./-e
#clear
echo *

Final note

If it is not clear from the tags, this article was not meant to be serious. If you however decide to use this in a real interview, please don’t make it the first question. You can ask it once you think the candidate is good enough and want to have a bit more of a interesting conversation with them.

If anything, I hope that reader got some intuition into why defensive programming in Bash is important.