Environment Variables

Table of Contents

1. Introduction
2. Environment Variable Expansion
3. GUI
4. CLI Option: --envVars
5. CLI Example
6. PowerShell Option: -EnvVars
7. PowerShell Example
8. Tips

Introduction

Servy allows you to define environment variables for the service process, enabling fine-grained control over the runtime context.

Environment variable expansion is supported in multiple areas of Servy configuration:

• Service binary paths (--path / -Path)
• Startup directories (--startupDir / -StartupDir)
• Process parameters (--params / -Params)
• Environment variables (--envVars / -EnvVars)

This makes it possible to reference existing system variables, user-defined variables, or paths dynamically in your configuration.

Environment Variable Expansion

Servy uses a sophisticated expansion engine that allows variables to reference each other. The resolution follows this specific order:

1. System Environment: All current system and process environment variables are loaded first.
2. Custom Overrides: Variables defined in the Environment Variables field (or --envVars) are added next. If a custom variable has the same name as a system variable, the custom value wins.
3. Cross-Reference Expansion: Finally, all variables are scanned for %VAR% placeholders. These placeholders are resolved using the final merged set of variables.

Example of Expansion Logic: If your system has TEMP=C:\Windows\Temp and you define:

• MY_ROOT=C:\ServyApp
• MY_LOGS=%MY_ROOT%\logs
• APP_TEMP=%TEMP%

The final environment seen by your process will be:

• MY_ROOT: C:\ServyApp
• MY_LOGS: C:\ServyApp\logs
• APP_TEMP: C:\Windows\Temp

Note

Variable Ordering and Circular References: Variables are resolved using a multi-pass fixed-point algorithm, so the order in which you define them does not matter — MY_LOGS=%MY_ROOT%\logs resolves correctly even if MY_ROOT is defined later in the list. The expansion engine runs up to 5 passes; chains deeper than that will leave unresolved %VAR% placeholders and Servy logs a warning ("Environment variable expansion reached maximum pass limit").

Avoid circular references: Setting A=%B% together with B=%A% is detected, logged as a warning, and leaves the literal placeholder in the final value because the cycle cannot be resolved.

GUI

The advanced tab in Servy allows setting environment variables for the service process:

CLI Option: --envVars

The --envVars command-line option lets you specify environment variables for the service process.

• Syntax: --envVars="VAR1=value1; VAR2=value2"
• Separate multiple variables with semicolons (;)
• Special characters can be escaped:
  • \= to escape =
  • \" to escape "
  • \; to escape ;
  • \\ to escape \
• Supports environment variable expansion. Example:
  --envVars="VAR1=%ProgramData%\MyApp; VAR2=%VAR1%\bin"
• Useful for setting runtime context without changing system-wide environment variables.

CLI Example

servy-cli install `
  --name="MyNodeService" `
  --description="My NodeJS Server" `
  --path="%ProgramFiles%\nodejs\node.exe" `
  --startupDir="C:\Apps\App" `
  --params="C:\Apps\App\index.js" `
  --startupType="Automatic" `
  --envVars="NODE_ENV=production; APP_CONFIG=C:\Apps\App\config.json"

PowerShell Option: -EnvVars

The -EnvVars parameter lets you define environment variables when installing a service via PowerShell.

• Type: string (semicolon-separated list, optional)
• Apply the same escaping rules as the CLI.
• Multiple variables are separated with semicolons (;)
• Variables are applied only to the service process, not system-wide.

PowerShell Example

Import-Module "C:\Program Files\Servy\Servy.psm1" -Force

$installParams = @{
    Name         = "MyNodeService"
    Description  = "My NodeJS Server"
    Path         = "C:\Program Files\nodejs\node.exe"
    StartupDir   = "C:\Apps\App"
    Params       = "C:\Apps\App\index.js"
    StartupType  = "Automatic"

    EnvVars      = "NODE_ENV=production; APP_CONFIG=C:\Apps\App\config.json"
}

Install-ServyService @installParams

Tips

• Case Insensitivity: Environment variable names are case-insensitive. Defining node_env will correctly override an existing NODE_ENV.
• Expansion Order: You can reference both existing system variables (like %ProgramData%) and other custom variables defined in the same list.
• Safe Escaping: If your variable value must contain a literal %, ensure it is not wrapped in another % or it may be treated as a failed expansion.
• Verification: To troubleshoot, if you aren't sure if your variables are applying correctly, run this to dump the environment to a file (PowerShell Admin):

  servy-cli install --name="EnvTest" --path="C:\Windows\System32\cmd.exe" --params="/c set > %TEMP%\servy_env.txt && pause" --envVars="MY_ROOT=C:\ServyApp; MY_LOGS=%MY_ROOT%\logs"
  servy-cli restart --name="EnvTest"
  Get-Content C:\Windows\Temp\servy_env.txt | Select-String "MY_LOGS"