curl exit codes: 6, 7, 22, 28, 35, 56, 60 and the rest

curl's exit code tells a script why a transfer failed: 0 means success, and every other value maps to a libcurl error such as 6 (could not resolve the host), 7 (could not connect), 22 (HTTP status 400 or above, only with -f) or 28 (timeout). The number is also printed in the error message, curl: (7) .... With -sS, curl hides the progress meter but still prints that message to stderr.

Common exit codes

The full list, more than 90 codes, is in the libcurl error documentation. Codes that are no longer used stay reserved, so the numbers never change meaning.

Seen in practice

Each command below fails in a different way against local addresses (ports 4303 and 4304) or with a malformed URL:

node -e 'require("http").createServer((q, r) => { if (q.url === "/slow") setTimeout(() => r.end("late\n"), 2500); else { r.statusCode = 500; r.end("error\n"); } }).listen(4303, "127.0.0.1"); setTimeout(() => process.exit(0), 5000)' &
sleep 1
run() { curl -sS "$@" 2>&1 | sed -E 's/[0-9]+ (ms|milliseconds)/N \1/'; echo "  -> exit ${PIPESTATUS[0]}"; }
run htp://127.0.0.1:4303/
run 'http://exa mple.com/'
run http://127.0.0.1:4304/
run -o /dev/null -f http://127.0.0.1:4303/
run -o /dev/null --max-time 1 http://127.0.0.1:4303/slow
wait

curl: (1) Protocol "htp" not supported
  -> exit 1
curl: (3) URL rejected: Malformed input to a URL function
  -> exit 3
curl: (7) Failed to connect to 127.0.0.1:4304 after N ms: Could not connect to server
  -> exit 7
curl: (22) The requested URL returned error: 500
  -> exit 22
curl: (28) Operation timed out after N milliseconds with 0 bytes received
  -> exit 28

Using the code in a script

curl -fsS --max-time 10 -o data.json https://api.example.org/data
case $? in
  0)  echo "ok" ;;
  6)  echo "DNS problem" ;;
  7)  echo "service down" ;;
  22) echo "HTTP error" ;;
  28) echo "timed out" ;;
  *)  echo "other curl error" ;;
esac

curl -w '%{exitcode}' (curl 7.75.0 and later) prints the same number from inside the write-out format.