# 🛠 Script Syntax and Parameter Substitution

When defining a CCP method, you provide two shell-based scripts:

- **`deploy-script`**: sets up the environment (e.g. installs dependencies, downloads files)
- **`execute-script`**: runs your algorithm using the inputs provided

These scripts support dynamic variable injection and conditional logic.

---

## 📌 Placeholder Syntax: `{{parameter_id}}`

Any input parameter defined in your `method.json` can be referenced in scripts using double curly braces.

```bash
echo "The input URL is {{file_url}}"
```

At runtime, CCP will substitute `{{file_url}}` with the actual value passed by the user.

---

## 📥 Downloading Files with `curl`

Use `curl` to download files passed as remote URLs:

```bash
curl -L {{file_url}} -o /ccp_data/input.txt
```

Notes:
- `-L` follows redirects (important for Google Drive, Dropbox, etc.)
- Save everything in `/ccp_data/` to make outputs accessible

---

## ⚠️ Optional Parameters

Use shell logic to **check if a parameter has been set** before using it:

```bash
[ -n "{{optional_param}}" ] && echo "Optional param was provided"
```

### Example

```bash
[ -n "{{mask_url}}" ] && curl -L {{mask_url}} -o /ccp_data/mask.png
```

This prevents the script from failing when the user leaves a field empty.

---

## 🔁 Building Dynamic Commands

For complex CLI tools, build your command step-by-step:

```bash
cmd="wordcloud_cli --text /ccp_data/input.txt"
cmd="$cmd --width {{width}} --height {{height}}"
[ -n "{{max_words}}" ] && cmd="$cmd --max_words {{max_words}}"
eval $cmd
```

This allows you to include optional flags only when they are present.

---

## 📦 Output Location

Always write result files to `/ccp_data/`, like:

```bash
python tool.py --output /ccp_data/results.csv
```

CCP will include these in the downloadable archive and display them in the UI.

---

## ✅ Quick Reference

| Task                  | Example                                      |
|-----------------------|----------------------------------------------|
| Inject parameter      | `{{input}}`                                  |
| Required download     | `curl -L {{url}} -o /ccp_data/file.txt`      |
| Optional download     | `[ -n "{{url}}" ] && curl ...`               |
| Dynamic command       | `cmd="..."; eval $cmd`                       |
| Output file           | Write to `/ccp_data/`                        |


## 🔗 Related Pages

- 🔣 [Defining method.json](./07_method_json.md)

- 🐧 [Docker runtime (ccpimage)](./02_defining_ccpimage.md)

- 🐍 [Python-based methods](./03_python_method.md)

- 🔧 [Workflow overview](./01_method_development_flow.md)