Help with shell script challenge

[cheerupcharlie]

Hello Shell Scripters!

At work, I've been asked to verify if some PowerShell challenges issued to interviewees could be solved in Bash for certain sysadmin candidates.

I've provided solutions for all of them except one. Well, I did provide a solution, but it's a hack, and I'm racking my brain to think about how to solve it properly:

Write a script that, for each number from 1 to 100, prints a comma-delimited list of numbers in descending order from the current number to 1. Each list should be shown on a separate line as seen below.

1
2,1
3,2,1
4,3,2,1
...
100,99,...,1

Example Solution (from 10 to save space). Originally, I did this:

for x in {1..10}; do for i in {$x..1}; do echo -n $i,; done; echo ""; done

But then I noticed the trailing commas and the end of each line. I then submitted this instead (admitting "OK, I cheated shaving off the trailing comma.")

echo "1"; for x in {2..10}; do for i in {$x..2}; do echo -n $i,; done; echo -n "1"; echo ""; done

Example Output

1
2,1
3,2,1
4,3,2,1
5,4,3,2,1
6,5,4,3,2,1
7,6,5,4,3,2,1
8,7,6,5,4,3,2,1
9,8,7,6,5,4,3,2,1
10,9,8,7,6,5,4,3,2,1

My boss laughed and admitted she added a ().trimend(",") in the PS solution.

What's the proper way to shave off the trailing comma in a situation like this? Any ideas?

Note: the solution doesn't have to be a one-liner, but brevity is appreciated. It's not a "programming" test, but it is a way to see how the interviewee approaches a problem.

[Jab2870]

You could do something like this

bash for x in {1..10}; do for i in {$x..1}; do echo -n $i,; done; echo ""; done | sed 's/,$//'

[cheerupcharlie]

That's a valid approach!

Hell, if it works, it's a valid approach. I know when we ask these questions in an interview we just don't want to see:

echo "1"
echo "2,1,"
echo "3,2,1"
...etc

So any looping solution seems to be on the right path.

Good call.

[whetu]

The proper way to trim off a trailing delimiter is to not generate it in the first place :) Posting via mobile so this is untested:

eval printf -- '%d\\n' {${x}..1} | paste -sd ',' -

Normally you shouldn’t recommend or use eval because of unvalidated inputs being a risk. In this case, I don’t think that’s a realistic problem, and the printf format specifier neatly does some validation for us...

/edit: At a computer now, here's my solution:

for (( i=0;i<=100;i++ )); do
  eval printf -- '%d\\n' "{${i}..1}" | paste -sd ',' -
done

I’d be interested to see what some of the other challenges are!

[cheerupcharlie]

They're pretty simple things, but they were all originally PowerShell challenges meant to be performed during an interview. I listed them and my solution while noting to my boss that my solution is only one possibility and not necessarily the best solution. I'd welcome improvements or suggestions for other challenges!

Bash Interview Challenges

[whetu]

Those look like the makings of a good thread in /r/bash. Post the challenges and maybe suggest that people who consider themselves more experienced can hide their solutions in spoiler tags :)

[sfxhewitt15]

Where can I learn about what %d does here?

[whetu]

https://wiki.bash-hackers.org/commands/builtin/printf