Docs: Refresh docs to organize and standardize reference materials. (#18403)

docs/cli/tutorials/automation.md

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+# Automate tasks with headless mode
+
+Automate tasks with Gemini CLI. Learn how to use headless mode, pipe data into
+Gemini CLI, automate workflows with shell scripts, and generate structured JSON
+output for other applications.
+
+## Prerequisites
+
+- Gemini CLI installed and authenticated.
+- Familiarity with shell scripting (Bash/Zsh).
+
+## Why headless mode?
+
+Headless mode runs Gemini CLI once and exits. It's perfect for:
+
+- **CI/CD:** Analyzing pull requests automatically.
+- **Batch processing:** Summarizing a large number of log files.
+- **Tool building:** Creating your own "AI wrapper" scripts.
+
+## How to use headless mode
+
+Run Gemini CLI in headless mode by providing a prompt as a positional argument.
+This bypasses the interactive chat interface and prints the response to standard
+output (stdout).
+
+Run a single command:
+
+```bash
+gemini "Write a poem about TypeScript"
+```
+
+## How to pipe input to Gemini CLI
+
+Feed data into Gemini using the standard Unix pipe `|`. Gemini reads the
+standard input (stdin) as context and answers your question using standard
+output.
+
+Pipe a file:
+
+```bash
+cat error.log | gemini "Explain why this failed"
+```
+
+Pipe a command:
+
+```bash
+git diff | gemini "Write a commit message for these changes"
+```
+
+## Use Gemini CLI output in scripts
+
+Because Gemini prints to stdout, you can chain it with other tools or save the
+results to a file.
+
+### Scenario: Bulk documentation generator
+
+You have a folder of Python scripts and want to generate a `README.md` for each
+one.
+
+1.  Save the following code as `generate_docs.sh`:
+
+    ```bash
+    #!/bin/bash
+
+    # Loop through all Python files
+    for file in *.py; do
+      echo "Generating docs for $file..."
+
+      # Ask Gemini CLI to generate the documentation and print it to stdout
+      gemini "Generate a Markdown documentation summary for @$file. Print the
+      result to standard output." > "${file%.py}.md"
+    done
+    ```
+
+2.  Make the script executable and run it in your directory:
+
+    ```bash
+    chmod +x generate_docs.sh
+    ./generate_docs.sh
+    ```
+
+    This creates a corresponding Markdown file for every Python file in the
+    folder.
+
+## Extract structured JSON data
+
+When writing a script, you often need structured data (JSON) to pass to tools
+like `jq`. To get pure JSON data from the model, combine the
+`--output-format json` flag with `jq` to parse the response field.
+
+### Scenario: Extract and return structured data
+
+1.  Save the following script as `generate_json.sh`:
+
+    ```bash
+    #!/bin/bash
+
+    # Ensure we are in a project root
+    if [ ! -f "package.json" ]; then
+      echo "Error: package.json not found."
+      exit 1
+    fi
+
+    # Extract data
+    gemini --output-format json "Return a raw JSON object with keys 'version' and 'deps' from @package.json" | jq -r '.response' > data.json
+    ```
+
+2.  Run `generate_json.sh`:
+
+    ```bash
+    chmod +x generate_json.sh
+    ./generate_json.sh
+    ```
+
+3.  Check `data.json`. The file should look like this:
+
+    ```json
+    {
+      "version": "1.0.0",
+      "deps": {
+        "react": "^18.2.0"
+      }
+    }
+    ```
+
+## Build your own custom AI tools
+
+Use headless mode to perform custom, automated AI tasks.
+
+### Scenario: Create a "Smart Commit" alias
+
+You can add a function to your shell configuration (like `.zshrc` or `.bashrc`)
+to create a `git commit` wrapper that writes the message for you.
+
+1.  Open your `.zshrc` file (or `.bashrc` if you use Bash) in your preferred
+    text editor.
+
+    ```bash
+    nano ~/.zshrc
+    ```
+
+    **Note**: If you use VS Code, you can run `code ~/.zshrc`.
+
+2.  Scroll to the very bottom of the file and paste this code:
+
+    ```bash
+    function gcommit() {
+      # Get the diff of staged changes
+      diff=$(git diff --staged)
+
+      if [ -z "$diff" ]; then
+        echo "No staged changes to commit."
+        return 1
+      fi
+
+      # Ask Gemini to write the message
+      echo "Generating commit message..."
+      msg=$(echo "$diff" | gemini "Write a concise Conventional Commit message for this diff. Output ONLY the message.")
+
+      # Commit with the generated message
+      git commit -m "$msg"
+    }
+    ```
+
+    Save your file and exit.
+
+3.  Run this command to make the function available immediately:
+
+    ```bash
+    source ~/.zshrc
+    ```
+
+4.  Use your new command:
+
+    ```bash
+    gcommit
+    ```
+
+    Gemini CLI will analyze your staged changes and commit them with a generated
+    message.
+
+## Next steps
+
+- Explore the [Headless mode reference](../../cli/headless.md) for full JSON
+  schema details.
+- Learn about [Shell commands](shell-commands.md) to let the agent run scripts
+  instead of just writing them.