fix(action): resolve command substitution in YAML inputs

docs/common-issues.md

@@ -1,6 +1,7 @@
 # Common issues
 
 - [Troubleshooting](#troubleshooting)
+  - [Command substitution in action inputs](#command-substitution-in-action-inputs)
   - [Create using an existing branch as the PR branch](#create-using-an-existing-branch-as-the-pr-branch)
 - [Frequently requested features](#use-case-create-a-pull-request-to-update-x-on-release)
   - [Disable force updates to existing PR branches](#disable-force-updates-to-existing-pr-branches)
@@ -8,6 +9,59 @@
 
 ## Troubleshooting
 
+### Command substitution in action inputs
+
+Shell command substitution (e.g., `$(date)`, backticks, or other shell expansions) does not work directly in GitHub Actions workflow inputs. This is a limitation of how GitHub Actions processes YAML inputs—they are treated as literal strings, not executed as shell commands.
+
+**This will NOT work:**
+```yml
+- name: Create Pull Request
+  uses: peter-evans/create-pull-request@v7
+  with:
+    commit-message: "Update Daily $(date -u +'%B %d, %Y')"
+    title: "Update Daily $(date -u +'%B %d, %Y')"
+```
+
+The `$(date -u +'%B %d, %Y')` will appear literally in your commit message and PR title instead of being replaced with the actual date.
+
+**Solution 1: Use a separate shell step with outputs (Recommended)**
+
+Execute the shell command in a separate step and pass the result to the action using GitHub Actions outputs:
+
+```yml
+- name: Set PR variables
+  id: vars
+  run: |
+    echo "date=$(date -u +'%B %d, %Y')" >> $GITHUB_OUTPUT
+    echo "commit_msg=Update Daily $(date -u +'%B %d, %Y')" >> $GITHUB_OUTPUT
+
+- name: Create Pull Request
+  uses: peter-evans/create-pull-request@v7
+  with:
+    commit-message: ${{ steps.vars.outputs.commit_msg }}
+    title: "Update Daily ${{ steps.vars.outputs.date }}"
+    body: Automated daily update.
+```
+
+**Solution 2: Use environment variables**
+
+Set environment variables in a shell step and reference them in the action:
+
+```yml
+- name: Set environment variables
+  run: |
+    echo "PR_DATE=$(date -u +'%B %d, %Y')" >> $GITHUB_ENV
+
+- name: Create Pull Request
+  uses: peter-evans/create-pull-request@v7
+  with:
+    commit-message: "Update Daily ${{ env.PR_DATE }}"
+    title: "Update Daily ${{ env.PR_DATE }}"
+    body: Automated daily update.
+```
+
+For more examples of using dynamic values in pull requests, see [Dynamic configuration using variables](examples.md#dynamic-configuration-using-variables).
+
 ### Create using an existing branch as the PR branch
 
 A common point of confusion is to try and use an existing branch containing changes to raise in a PR as the `branch` input. This will not work because the action is primarily designed to be used in workflows where the PR branch does not exist yet. The action creates and manages the PR branch itself.