Support self-hosted runner that does not set GITHUB_OUTPUT

Fixes #17

CHANGELOG.md

@@ -10,6 +10,8 @@ Note: In this file, do not use the hard wrap in the middle of a sentence for com
 
 ## [Unreleased]
 
+- Support self-hosted runner that does not set `GITHUB_OUTPUT` environment variable. ([#17](https://github.com/taiki-e/create-gh-release-action/pull/17))
+
 ## [1.6.1] - 2022-10-14
 
 - Fix invalid version format check introduced in 1.4.0.

main.sh

@@ -113,7 +113,14 @@ fi
 # https://cli.github.com/manual/gh_release_create
 GITHUB_TOKEN="${token}" gh release create "${release_options[@]}" --title "${title}" --notes "${notes:-}"
 
-# set (computed) prefix and version outputs for future step use
+# Set (computed) prefix and version outputs for future step use.
 computed_prefix=${tag%"${version}"}
-echo "computed-prefix=${computed_prefix}" >>"${GITHUB_OUTPUT}"
-echo "version=${version}" >>"${GITHUB_OUTPUT}"
+if [[ -n "${GITHUB_OUTPUT:-}" ]]; then
+    echo "computed-prefix=${computed_prefix}" >>"${GITHUB_OUTPUT}"
+    echo "version=${version}" >>"${GITHUB_OUTPUT}"
+else
+    # Self-hosted runner may not set GITHUB_OUTPUT.
+    warn "GITHUB_OUTPUT is not set; skip setting 'computed-prefix' and 'version' outputs"
+    echo "computed-prefix: ${computed_prefix}"
+    echo "version: ${version}"
+fi