Chapter 9: Environment Variables and Configuration Management¶

Learning Objectives¶

By the end of this chapter, you will be able to:

1. Understand the difference between user and system environment variables on macOS.
2. Configure and manage .bash_profile and .bashrc, including macOS-specific considerations.
3. Use Launch Agents and Daemons to manage environment variables and scripts.

Introduction: Why Environment Configuration Matters¶

Environment variables influence how Bash scripts run and interact with macOS. They define system-wide paths, user preferences, and credentials. Misconfigurations can lead to unexpected behavior, security issues, or broken automation. This chapter shows you how to manage these settings correctly.

9.1 User vs System Environment¶

• User Environment Variables: Defined in your user’s shell config files like .bash_profile or .bashrc. They apply only when you run a shell as your user.
• System Environment Variables: Defined in system files like /etc/profile or /etc/paths. They affect all users and sometimes system daemons.

Check your current environment:

env

Or print a single variable:

echo "$PATH"
echo "$HOME"

Modifying System Variables Safely¶

• On macOS, modify /etc/paths to add system-wide directories.
• For sensitive scripts, prefer user-level variables unless you need system scope.

9.2 .bash_profile, .bashrc, and macOS Quirks¶

Traditionally:

• .bash_profile runs for login shells.
• .bashrc runs for interactive non-login shells.

macOS Terminal launches login shells by default, so your .bash_profile is often the right place to export variables.

Example .bash_profile:

export PATH="$HOME/bin:$PATH"
export EDITOR="nano"

To ensure .bashrc runs, source it in .bash_profile:

if [ -f "$HOME/.bashrc" ]; then
  source "$HOME/.bashrc"
fi

Tip: Always test changes with a new Terminal window.

9.3 Managing Config with Launch Agents and Daemons¶

macOS uses launchd to manage user and system processes. Sometimes you need to ensure environment variables are available to GUI apps or background tasks.

• Launch Agents run as a user.
• Launch Daemons run as root.

Example: Create a user Launch Agent to set a variable and run a script.

1. Create a plist file in ~/Library/LaunchAgents/:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.example.setenv</string>
  <key>ProgramArguments</key>
  <array>
    <string>/bin/bash</string>
    <string>-c</string>
    <string>export MY_VAR=hello && echo $MY_VAR > /tmp/my_var.txt</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
</dict>
</plist>

1. Load the agent:

launchctl load ~/Library/LaunchAgents/com.example.setenv.plist

1. Verify the variable was set:

cat /tmp/my_var.txt

Tip: For system-wide daemons, use /Library/LaunchDaemons/ and ensure permissions are correct.

Chapter 9 Exercise¶

Manage your environment:

1. Add a custom PATH or variable to your .bash_profile.
2. Test with env and echo.
3. Create a Launch Agent that runs a small script and sets a variable.
4. Inspect the logs with log show or Console.

Example shell snippet:

export BACKUP_DIR="$HOME/backups"
mkdir -p "$BACKUP_DIR"
echo "Backups will go to: $BACKUP_DIR"

macOS Scripting Tips¶

• Always back up .bash_profile and .bashrc before changes.
• Use descriptive variable names.
• Test with a new shell session to confirm behavior.
• Use launchctl list to verify active agents and daemons.