Exit codes: $?, && and ||

Cheat sheet

• ls /nope; echo $? 2 — code of the last command
• grep -q root /etc/passwd && echo found second runs after code 0
• mkdir /srv/app || echo "failed" >&2 second runs after non-zero
• if grep -q '^backup:' /etc/passwd; then echo found; fi
• rc=$? save the code before it's lost
• exit 1 leave a script with code 1
• false | true; echo "${PIPESTATUS[@]}" 1 0 — code of every stage
• set -o pipefail a failed stage fails it all