> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/dotandev/envcheck/llms.txt
> Use this file to discover all available pages before exploring further.

# Environment Variables

> Validate environment variables and their values

## Overview

The `env_vars` section checks for the presence of environment variables and optionally validates their values against regex patterns. This ensures critical configuration values are set before running your application.

## Configuration

Each environment variable check is defined by an `EnvVarCheck` struct (src/config.rs:31) with the following fields:

<ParamField path="name" type="string" required>
  The name of the environment variable to check.
</ParamField>

<ParamField path="required" type="boolean" default="true">
  Whether the environment variable must be set. If `true`, validation fails when the variable is not defined.
</ParamField>

<ParamField path="pattern" type="string" optional>
  A regex pattern to validate the variable's value. If specified, the value must match this pattern.
</ParamField>

## Examples

### Basic Presence Check

Check that an environment variable is set:

```yaml theme={null}
env_vars:
  - name: DATABASE_URL
    required: true
```

### Optional Variables

Mark variables as optional when they have sensible defaults:

```yaml theme={null}
env_vars:
  - name: NODE_ENV
    required: false
  - name: LOG_LEVEL
    required: false
```

### Pattern Validation

Validate that environment variable values match expected formats:

```yaml theme={null}
env_vars:
  - name: RAILS_ENV
    required: false
    pattern: "^(development|test|production)$"
  
  - name: DEBUG
    required: false
    pattern: "^(True|False|1|0)$"
  
  - name: PORT
    required: true
    pattern: "^[0-9]{1,5}$"
```

## Real-World Examples

<CodeGroup>
  ```yaml Node.js Project theme={null}
  version: "1"

  env_vars:
    - name: NODE_ENV
      required: false
    - name: DATABASE_URL
      required: true
  ```

  ```yaml Django Project theme={null}
  version: "1"

  env_vars:
    - name: SECRET_KEY
      required: true
    - name: DATABASE_URL
      required: true
    - name: DEBUG
      required: false
      pattern: "^(True|False|1|0)$"
  ```

  ```yaml Rails Project theme={null}
  version: "1"

  env_vars:
    - name: DATABASE_URL
      required: true
    - name: RAILS_ENV
      required: false
      pattern: "^(development|test|production)$"
  ```

  ```yaml Rust Project theme={null}
  version: "1"

  env_vars:
    - name: RUST_LOG
      required: false
    - name: DATABASE_URL
      required: false
  ```

  ```yaml Go Project theme={null}
  version: "1"

  env_vars:
    - name: GOPATH
      required: false
    - name: GOBIN
      required: false
  ```
</CodeGroup>

## Pattern Syntax

The `pattern` field uses standard regex syntax. Here are common patterns:

### Exact Values

```yaml theme={null}
# Must be one of: development, test, production
pattern: "^(development|test|production)$"
```

### Boolean Values

```yaml theme={null}
# Common boolean representations
pattern: "^(true|false|1|0|yes|no)$"

# Python-style booleans
pattern: "^(True|False|1|0)$"
```

### Numeric Ranges

```yaml theme={null}
# Port numbers (1-65535)
pattern: "^([1-9][0-9]{0,3}|[1-5][0-9]{4}|6[0-4][0-9]{3}|65[0-4][0-9]{2}|655[0-2][0-9]|6553[0-5])$"

# Simple 1-5 digit number
pattern: "^[0-9]{1,5}$"
```

### URL Validation

```yaml theme={null}
# Simple URL pattern
pattern: "^https?://.*"

# Database URL
pattern: "^postgres(ql)?://.*"
```

### Custom Formats

```yaml theme={null}
# Alphanumeric only
pattern: "^[a-zA-Z0-9]+$"

# Semantic version
pattern: "^[0-9]+\\.[0-9]+\\.[0-9]+$"
```

<Note>
  Remember to escape backslashes in YAML strings. Use `\\` for a single backslash in regex patterns.
</Note>

## Default Behavior

From the struct definition in src/config.rs:31:

* `name`: Required field, no default
* `required`: Defaults to `true`
* `pattern`: Defaults to `None` (no pattern validation)

<Warning>
  When `required: true`, validation fails if:

  * The environment variable is not set
  * The variable is set but its value doesn't match the `pattern` (if specified)
</Warning>

<Tip>
  Use `required: false` with a `pattern` to validate optional variables only when they're set. This allows developers to omit the variable entirely while ensuring correct values when provided.
</Tip>