Simplify shell script

Author: hmac

.github/workflows/post-pr-comment.yml

@@ -42,24 +42,20 @@ jobs:
           COMMENT_AUTHOR="github-actions[bot]"
           PR_NUMBER="$(grep -o '^[0-9]\+$' pr_number.txt)"
 
-          # comment_id.txt may be empty if there is no existing comment
-          if [ -s comment_id.txt ]
-          then
-            COMMENT_ID="$(grep -o '^[0-9]\+$' comment_id.txt)"
-          fi
+          # If there is no existing comment, comment_id.txt will contain just a
+          # newline (due to jq & gh behaviour). This will cause grep to fail, so
+          # we catch that.
+          COMMENT_ID=$(grep -o '^[0-9]\+$' comment_id.txt || true)
 
-          if [ -z "$COMMENT_ID" ]
+          if [ $COMMENT_ID ]
           then
-            # Create new comment
-            jq --rawfile body comment_body.txt '{"body":$body}' -n | gh api "repos/${GITHUB_REPOSITORY}/issues/${PR_NUMBER}/comments" -X POST --input -
-          else
             # Fetch existing comment, and validate:
             # - comment belongs to the PR with number $PR_NUMBER
             # - comment starts with the expected prefix ("QHelp previews")
             # - comment author is github-actions[bot]
             FILTER="select(.issue_url | test(\"${GITHUB_REPOSITORY}/issues/${PR_NUMBER}$\")) \
                                       | select(.body | test(\"^${COMMENT_PREFIX}\"))         \
-                                      | select(.user.login == \"${COMMENT_AUTHOR}\")           \
+                                      | select(.user.login == \"${COMMENT_AUTHOR}\")         \
                                       | .id"
             COMMENT_ID=$(gh api "repos/${GITHUB_REPOSITORY}/issues/comments/${COMMENT_ID}" | jq "${FILTER}")
             if [ $COMMENT_ID ]
@@ -69,6 +65,9 @@ jobs:
             else
               echo "Comment ${COMMENT_ID} did not pass validations: not editing."
             fi
+          else
+            # Create new comment
+            jq --rawfile body comment_body.txt '{"body":$body}' -n | gh api "repos/${GITHUB_REPOSITORY}/issues/${PR_NUMBER}/comments" -X POST --input -
           fi
         env:
           GITHUB_TOKEN: ${{ github.token }}