Cheat sheet & self-check

Pick an answer to see if you got it, and why.

1. Q1. What's wrong with 'name = Asha' in Bash?

   1. ANothing
   2. BSpaces around = make Bash run a command called 'name' with arguments '=' and 'Asha'
   3. CVariables must be uppercase
   4. DIt needs a semicolon
   Show answer

   B. Assignments must be written name=value with no spaces. It's the most common first Bash error.

   From lesson 01 · Scripts, variables & quoting

2. Q2. file='my report.txt'; rm $file — what happens?

   1. ADeletes 'my report.txt'
   2. BTries to delete two files, 'my' and 'report.txt'
   3. CSyntax error
   4. DNothing
   Show answer

   B. Unquoted variables are split on spaces. Always quote: rm "$file".

   From lesson 01 · Scripts, variables & quoting

3. Q3. What does an exit status of 0 mean?

   1. AFailure
   2. BSuccess
   3. CThe script was empty
   4. DZero lines of output
   Show answer

   B. By convention 0 = success and anything else (1–255) = some kind of failure. if, &&, || and set -e all rely on it.

   From lesson 01 · Scripts, variables & quoting

4. Q4. Which prints the literal text $HOME?

   1. Aecho "$HOME"
   2. Becho '$HOME'
   3. Cecho $HOME
   4. Decho $(HOME)
   Show answer

   B. Single quotes stop all expansion. Double quotes still expand variables.

   From lesson 01 · Scripts, variables & quoting

5. Q5. Which test checks that a directory exists?

   1. A[[ -f /srv/app ]]
   2. B[[ -d /srv/app ]]
   3. C[[ -e -dir /srv/app ]]
   4. D[[ /srv/app ]]
   Show answer

   B. -d is true for directories, -f for regular files, -e for anything that exists.

   From lesson 02 · Conditions & loops

6. Q6. Why use 'while IFS= read -r line' instead of 'for line in $(cat file)'?

   1. AIt's shorter
   2. BThe for version splits on every space and expands wildcards; while-read handles each line exactly as written
   3. Cfor can't read files
   4. Dread is faster at math
   Show answer

   B. for over $(cat) iterates words, not lines. IFS= keeps leading spaces, and -r keeps backslashes.

   From lesson 02 · Conditions & loops

7. Q7. How do you compare numbers in Bash?

   1. A[[ $a > $b ]]
   2. B(( a > b )) or [[ $a -gt $b ]]
   3. Cif a > b
   4. D[ a -bigger b ]
   Show answer

   B. Inside [[ ]], > compares strings alphabetically. Use (( )) for arithmetic, or -gt/-lt/-eq in [[ ]].

   From lesson 02 · Conditions & loops

8. Q8. Why write "$@" instead of $* when passing arguments on?

   1. AIt's shorter
   2. B"$@" keeps each argument separate and intact, even with spaces
   3. C$* is deprecated
   4. DThey're identical
   Show answer

   B. Unquoted $* and $@ re-split arguments. "$@" preserves exactly what the caller passed.

   From lesson 03 · Functions & arguments

9. Q9. What does 'local' do inside a function?

   1. AMakes the variable read-only
   2. BLimits the variable to the function, so it doesn't overwrite a global of the same name
   3. CExports it
   4. DDeletes it
   Show answer

   B. Without local, every assignment in a function changes the global variable. That's a common source of subtle bugs.

   From lesson 03 · Functions & arguments

10. Q10. Where should a script print error messages?

    1. Astdout
    2. Bstderr (>&2), so they don't mix with data another program might read
    3. CA file only
    4. DNowhere
    Show answer

    B. stdout is for the script's output (possibly piped into another tool); stderr is for diagnostics.

    From lesson 03 · Functions & arguments

11. Q11. Which command changes 'debug' to 'info' in config.ini in place, keeping a backup?

    1. Ased 's/debug/info/g' config.ini
    2. Bsed -i.bak 's/debug/info/g' config.ini
    3. Cawk 's/debug/info/'
    4. Dgrep -r debug info
    Show answer

    B. Without -i, sed only prints the result. -i.bak edits the file and saves the original as config.ini.bak.

    From lesson 04 · Text processing

12. Q12. What does awk -F: '{print $1}' /etc/passwd print?

    1. AThe whole file
    2. BThe first colon-separated field of each line: the usernames
    3. CLine 1
    4. DThe number of users
    Show answer

    B. -F: sets the field separator to ':'. $1 is the first field.

    From lesson 04 · Text processing

13. Q13. kubectl get pods -o json | jq -r '.items[].metadata.name' prints…

    1. AThe JSON of every pod
    2. BEach pod's name on its own line, without quotes
    3. CThe number of pods
    4. DOnly running pods
    Show answer

    B. .items[] iterates the list, .metadata.name selects the field, and -r prints raw strings without JSON quotes.

    From lesson 04 · Text processing

14. Q14. What does 'set -o pipefail' change?

    1. APipes run faster
    2. BA pipeline fails if ANY command in it fails, not just the last one
    3. CPipes are disabled
    4. DOutput is buffered
    Show answer

    B. Without pipefail, 'curl … | tar x' reports tar's status only, hiding a failed download.

    From lesson 05 · Safe scripts

15. Q15. Why is 'rm -rf "$DIR"/' dangerous, and what's the fix?

    1. AIt isn't dangerous
    2. BIf DIR is empty it becomes 'rm -rf /'; use "${DIR:?}" (or set -u) so the script aborts instead
    3. Crm doesn't accept quotes
    4. D-f is too slow
    Show answer

    B. ${DIR:?} makes Bash stop with an error when DIR is unset or empty, before rm ever runs.

    From lesson 05 · Safe scripts

16. Q16. What makes a script idempotent?

    1. AIt runs quickly
    2. BRunning it twice leaves the system in the same state as running it once
    3. CIt never prints anything
    4. DIt uses functions
    Show answer

    B. Idempotent steps (check before acting, mkdir -p, 'ensure' rather than 'create') make re-runs after a partial failure safe.

    From lesson 05 · Safe scripts

17. Q17. A cron job sometimes runs longer than its interval, and two copies corrupt data. Simplest fix?

    1. ARun it less often
    2. BTake a lock with flock so a second copy exits (or waits) while the first runs
    3. CAdd sleep 60
    4. DUse nohup
    Show answer

    B. flock on a lock file serialises runs reliably, and the lock is released automatically when the process exits.

    From lesson 05 · Safe scripts

18. Q18. A script works in your terminal but fails from cron with 'command not found'. Most likely cause?

    1. Acron is broken
    2. Bcron runs with a minimal environment and PATH; use full paths or set PATH in the script
    3. CThe script needs root
    4. Dcron only supports sh
    Show answer

    B. cron doesn't load your .bashrc. PATH is minimal, and other variables are missing. Set what you need explicitly.

    From lesson 06 · Scheduling & automation

19. Q19. What does the cron line '*/10 9-17 * * 1-5' mean?

    1. AEvery 10 hours
    2. BEvery 10 minutes, between 09:00 and 17:59, Monday to Friday
    3. CAt 09:10 daily
    4. DTen times a day
    Show answer

    B. Fields are minute, hour, day-of-month, month, day-of-week. */10 = every 10 minutes; 9-17 = hours 9 to 17; 1-5 = Mon–Fri.

    From lesson 06 · Scheduling & automation

20. Q20. What does Persistent=true do in a systemd timer?

    1. AKeeps the job running forever
    2. BIf the machine was off at the scheduled time, runs the job soon after boot
    3. CStores logs permanently
    4. DPrevents the timer from being disabled
    Show answer

    B. Persistent timers catch up on missed runs, which is useful for laptops, VMs and servers that reboot during the window.

    From lesson 06 · Scheduling & automation

21. Q21. shellcheck warns SC2086 'Double quote to prevent globbing and word splitting'. What should you do?

    1. ADisable shellcheck
    2. BQuote the variable ("$var") unless splitting is intended, and then document it
    3. CRename the variable
    4. DAdd set -x
    Show answer

    B. SC2086 is the most common real bug in Bash scripts. Quoting fixes it; intentional exceptions get a '# shellcheck disable=SC2086' with a reason.

    From lesson 07 · Testing & linting

22. Q22. How do you make functions in a script testable with bats without running the whole script?

    1. ACopy them into the test
    2. BPut the main logic in a main function and only call it when the file is executed, not when it's sourced
    3. CUse global variables
    4. DIt's impossible
    Show answer

    B. A guard like [[ "${BASH_SOURCE[0]}" == "$0" ]] && main "$@" lets tests 'source' the file to load functions without side effects.

    From lesson 07 · Testing & linting

23. Q23. Why run shellcheck and tests in CI?

    1. ATo slow down merges
    2. BSo every change is checked automatically before it's merged and deployed
    3. CBecause servers can't run bash
    4. DTo format code for you
    Show answer

    B. Automated checks on every pull request catch regressions consistently, without relying on reviewers noticing quoting bugs.

    From lesson 07 · Testing & linting

24. Q24. Why does the script exit 3 when curl is missing, instead of 1?

    1. A3 is luckier
    2. BDistinct exit codes let callers tell 'a check failed' apart from 'the checker itself is broken'
    3. Ccurl requires it
    4. Dsystemd needs code 3
    Show answer

    B. A missing tool is a problem with the monitoring, not with the service. Different codes lead to different alerts and fixes.

    From lesson 08 · Capstone: a real ops script

25. Q25. Why log in 'key=value' format?

    1. AIt looks nice
    2. BIt's easy to search and parse in the journal or a log platform (check=api status=fail latency_ms=…)
    3. CBash requires it
    4. DIt's smaller
    Show answer

    B. Structured logs turn into dashboards and alerts with no extra parsing work.

    From lesson 08 · Capstone: a real ops script