fix(repo): report download failures in install.sh

[Sunasuna24]

Fixes #3040.

Checklist

• Tests added / updated
• Docs added / updated

Does this PR introduce a breaking change?

• Yes
• No

Additional context

Three lines in the download block combined to swallow connection-level failures, so curl -L .../install.sh | sh exited non-zero with no explanation at all. Reasoning is in #3040.

-STATUS=$(curl -sL -w %{http_code} -o "$SRC" "$URL")
-if [ $STATUS -ge 200 ] & [ $STATUS -le 308 ]; then
+STATUS=$(curl -sL -w "%{http_code}" -o "$SRC" "$URL") || STATUS=000
+if [ "$STATUS" -ge 200 ] && [ "$STATUS" -le 308 ]; then
   mv "$SRC" "$DEST"
   chmod +x "$DEST"
   echo "Spectral was installed to: ${DEST}"
 else
-  rm "$SRC"
+  rm -f "$SRC"

• || STATUS=000 stops set -eu from terminating on the assignment, so a curl failure now falls through to the error branch that already exists instead of exiting with curl's own status.
• & → && makes the lower bound actually apply. With & the first test is backgrounded and its result discarded, leaving the condition as -le 308 alone — which would accept 000 as success once the line above stops exiting early. The two have to change together.
• rm -f lets the error branch finish when curl never created the output file; previously rm failed there and set -e killed the script before the message on the next line.

The two quoting changes sit on lines already being touched and clear the remaining shellcheck notes.

Verification

case	before	after
no network	exit 6, no output	Error requesting. Download binary from <URL>, exit 1
version that doesn't exist (404)	already correct	unchanged
normal install	works	works

Commands and output

# no network
$ docker run --rm --network none --user root -w /tmp \
    -v "$PWD/scripts/install.sh:/install.sh:ro" \
    curlimages/curl:latest sh /install.sh 6.16.3; echo "exit: $?"
Installing on Alpine Linux.
Error requesting. Download binary from https://github.com/stoplightio/spectral/releases/download/v6.16.3/spectral-alpine-arm64
exit: 1

# version that doesn't exist
$ ... sh /install.sh 99.99.99; echo "exit: $?"
Installing on Alpine Linux.
Error requesting. Download binary from https://github.com/stoplightio/spectral/releases/download/v99.99.99/spectral-alpine-arm64
exit: 1

# normal install, unchanged
$ ... sh /install.sh 6.16.3; echo "exit: $?"
Spectral was installed to: /usr/local/bin/spectral
exit: 0
$ ls -l /usr/local/bin/spectral && /usr/local/bin/spectral --version
-rwxr-xr-x 1 root root 78334324 /usr/local/bin/spectral
6.16.3

shellcheck on this file goes from 5 findings to 0, including the one it classifies as an error:

54:24: error: Use && for logical AND. Single & will background and return true. [SC2265]

No tests are included — there's no harness for the shell installer, and reproducing the failure needs a network-isolated container. Happy to add coverage if you'd like it.

[Copilot]

Pull request overview

Fixes silent installer failures by routing curl connection errors through the existing error path.

Changes:

• Handles failed downloads without premature set -e termination.
• Corrects HTTP status validation and safely removes missing files.

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