Set PROTOC environment variable when installing protoc

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]
 
+- Set the `PROTOC` environment variable when installing `protoc` if it has not already been set.
+
 ## [1.9.0] - 2022-08-01
 
 - Support `protoc`.

main.sh

@@ -239,6 +239,14 @@ for tool in "${tools[@]}"; do
                 *) bail "unsupported OSTYPE '${OSTYPE}' for ${tool}" ;;
             esac
             download "${url}" /usr/local/bin "bin/protoc${exe}"
+            if [[ -z "${PROTOC:-}" ]]; then
+                info "setting PROTOC environment variable"
+                if [[ -d /usr/local/bin ]]; then
+                    echo "PROTOC=/usr/local/bin/protoc${exe}" >>"${GITHUB_ENV}"
+                else
+                    echo "PROTOC=${HOME}/.install-action/bin/protoc${exe}" >>"${GITHUB_ENV}"
+                fi
+            fi
             ;;
         shellcheck)
             # https://github.com/koalaman/shellcheck/releases