# Troubleshooting parameter handling issues
<a name="parameter-troubleshooting"></a>

## Common parameter handling issues
<a name="common-parameter-issues"></a>

**Environment variables not available during execution**  
**Problem:** Commands fail because environment variables (`SSM_{{parameter-name}}`) are not found.  
**Possible causes:**  
+ SSM Agent version doesn't support environment variable interpolation
+ `interpolationType` is not set to `ENV_VAR`
+ Parameter name doesn't match the expected environment variable name
**Solution:**  
+ Verify SSM Agent version is 3.3.2746.0 or later
+ Add fallback logic for older agent versions:

  ```
  if [ -z "${SSM_parameterName+x}" ]; then
      export SSM_parameterName="{{parameterName}}"
  fi
  ```

**Parameter values containing special characters**  
**Problem:** Commands fail when parameter values contain spaces, quotes, or other special characters.  
**Solution:**  
+ Use proper quoting when referencing environment variables:

  ```
  # Correct
  echo "$SSM_{{parameter-name}}"
  
  # Incorrect
  echo $SSM_{{parameter-name}}
  ```
+ Add input validation using `allowedPattern` to restrict special characters

**Inconsistent behavior across platforms**  
**Problem:** Parameter handling works differently on Linux and Windows Server systems.  
**Solution:**  
+ Use platform-specific environment variable syntax:

  ```
  # PowerShell
  $env:SSM_{{parameter-name}}
  
  # Bash
  $SSM_{{parameter-name}}
  ```
+ Use platform-specific precondition checks in your document

**Parameter values not properly escaped**  
**Problem:** Command injection vulnerabilities despite using environment variable interpolation.  
**Solution:**  
+ Always use proper escaping when including parameter values in commands:

  ```
  # Correct
  mysql_command="mysql -u \"$SSM_username\" -p\"$SSM_password\""
  
  # Incorrect
  mysql_command="mysql -u $SSM_username -p$SSM_password"
  ```

## Parameter validation tips
<a name="parameter-validation"></a>

Use these techniques to validate your parameter handling:

1. Test environment variable availability:

   ```
   #!/bin/bash
   # Print all SSM_ environment variables
   env | grep ^SSM_
   
   # Test specific parameter
   if [ -n "$SSM_parameter" ]; then
       echo "Parameter is available"
   else
       echo "Parameter is not available"
   fi
   ```

1. Verify parameter patterns:

   ```
   parameters:
     myParameter:
       type: String
       allowedPattern: "^[a-zA-Z0-9_-]+$"
       description: "Test this pattern with sample inputs"
   ```

1. Include error handling:

   ```
   if [[ ! "$SSM_parameter" =~ ^[a-zA-Z0-9_-]+$ ]]; then
       echo "Parameter validation failed"
       exit 1
   fi
   ```