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# Rego Basics

## 📚 Learning Materials

* [**Basics.md**](/notes/devops/open-policy-agent/rego-basics/basics.md) - Complete theoretical guide to Rego fundamentals
* [**Understanding-OPA-Eval-Results.md**](/notes/devops/open-policy-agent/rego-basics/understanding-opa-eval-results.md) - Guide to interpreting `opa eval` command results

## Getting Started

This directory contains practical examples to help you learn Rego step by step:

### 1. Basic Policy (`01-simple-policy.rego`)

* Basic allow/deny rules
* Simple conditions
* Default values
* Helper rules

**Test with:**

```bash
opa eval -d 01-simple-policy.rego -i input1.json "data.simple_policy.allow"
opa eval -d 01-simple-policy.rego -i input2.json "data.simple_policy.allow"
```

### 2. RBAC Policy (`02-rbac-policy.rego`)

* Role-based access control
* Time-based restrictions
* Violation messages
* Complex conditions

**Test with:**

```bash
opa eval -d 02-rbac-policy.rego -i rbac-input.json "data.rbac_policy"
```

### 3. Arrays and Objects (`03-arrays-objects.rego`)

* Array comprehensions
* Object comprehensions
* Set comprehensions
* Complex data structures

**Test with:**

```bash
opa eval -d 03-arrays-objects.rego "data.array_object_examples.active_users"
```

## Practice Exercises

1. **Modify the simple policy** to add a new rule for "editor" role
2. **Create a new input file** with different user roles and test the RBAC policy
3. **Experiment with array comprehensions** in the arrays-objects example
4. **Write a new policy** for file system permissions

## Useful OPA Commands

```bash
## Install OPA (if not installed)
curl -L -o opa https://github.com/open-policy-agent/opa/releases/latest/download/opa_linux_amd64
chmod +x opa
sudo mv opa /usr/local/bin/

## Format Rego files
opa fmt --diff *.rego

## Interactive REPL
opa run policy.rego

## Test policies (requires _test.rego files)
opa test .
```

## Next Steps

1. Try the [OPA Playground](https://play.openpolicyagent.org/)
2. Write test files for your policies
3. Explore OPA integration with applications
4. Learn about OPA performance optimization
5. Study real-world policy examples


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