Zero-Configuration Terminal Output: Write Once, Works Everywhere

October 26, 2025 · 7 min read

Founder @ Cloud Posse

Atmos now features intelligent terminal output that adapts to any environment automatically. Developers can write code assuming a full-featured terminal, and Atmos handles the rest - capability detection, color adaptation, and secret masking happen transparently. No more capability checking, manual color detection, or masking code. Just write clean, simple output code and it works everywhere.

The Problem with Traditional CLI Output

Most CLI tools force developers to make painful choices:

// Traditional approach - painful!
if isatty.IsTerminal(os.Stdout.Fd()) {
    // Using Charm Bracelet's lipgloss for styling
    successStyle := lipgloss.NewStyle().Foreground(lipgloss.Color("10"))
    fmt.Println(successStyle.Render("Success!"))
} else {
    fmt.Println("Success!")  // Plain for pipes
}

// And don't forget to mask secrets!
if containsSecret(output) {
    output = maskSecrets(output)
}
fmt.Println(output)

What Existing Solutions Don't Solve

While Charm Bracelet's Lip Gloss and similar libraries handle rendering beautifully (styled components, layouts, colors), they don't solve critical infrastructure CLI challenges:

Secret Masking: No automatic redaction of sensitive data across all output channels
Centralized I/O Control: Output scattered across stdout/stderr without unified masking
Security-First Design: Secrets can leak through unmasked channels or error messages
Atmos-Specific Requirements: Infrastructure tools handle AWS keys, API tokens, and sensitive configs that must never appear in logs

This leads to:

🚫 Duplicated capability checking throughout the codebase
🚫 Inconsistent output behavior across commands
🚫 Secrets accidentally leaked to logs (the primary driver for this work)
🚫 Broken pipelines when output assumptions change
🚫 Difficult testing (mocking TTY detection is painful)

The Atmos Solution: Write Once, Works Everywhere

Atmos's I/O system complements Charm Bracelet by adding the infrastructure-critical layer that rendering libraries don't provide: centralized I/O control with automatic secret masking. Lip Gloss handles the beautiful rendering; Atmos ensures that rendering never exposes sensitive data.

With Atmos's new I/O system, developers write code once:

// Atmos approach - simple!
ui.Success("Deployment complete!")

That's it. No capability checking, no color detection, no TTY handling. The system automatically:

🎨 Color Degradation

TrueColor terminal (iTerm2, Windows Terminal): Full 24-bit colors
256-color terminal: 256-color palette
16-color terminal (basic xterm): ANSI colors
No color (CI, NO_COLOR=1, pipes): Plain text

📏 Width Adaptation

Wide terminal (120+ cols): Uses full width with proper wrapping
Narrow terminal (80 cols): Wraps at 80 characters
Config override: Respects atmos.yaml settings.terminal.max_width
Unknown width: Sensible defaults

🔍 TTY Detection

Interactive terminal: Full styling, colors, icons, formatting
Piped (atmos deploy | tee): Plain text automatically
Redirected (atmos > file): Plain text automatically
CI environment: Detects CI and disables interactivity

🎭 Markdown Rendering

ui.Markdown("# Deployment Report\n\n**Status:** Success")

Color terminal: Styled markdown with colors, bold, headers
No-color terminal: Plain text formatting (notty style)
Render failure: Gracefully falls back to plain content

🔒 Automatic Secret Masking

data.WriteJSON(config)  // Contains AWS_SECRET_ACCESS_KEY

Output automatically masked:

{
  "aws_access_key_id": "AKIAIOSFODNN7EXAMPLE",
  "aws_secret_access_key": "***MASKED***"
}

No manual redaction needed. The system automatically detects and masks:

AWS access keys and secrets (AKIA*, ASIA*)
Sensitive environment variable patterns
Common token formats
JSON/YAML quoted variants

🎯 Channel Separation

// Data to stdout (pipeable)
data.WriteJSON(result)

// Messages to stderr (human-readable)
ui.Info("Processing components...")
ui.Success("Deployment complete!")

Users can now safely pipe data while seeing status:

atmos terraform output | jq .vpc_id
# Still sees progress on stderr:
# ℹ Loading configuration...
# ✓ Output retrieved!

📝 Logging vs Terminal Output

Important distinction: This I/O system is for terminal output (user-facing data and messages), not logging (system events and debugging).

Terminal Output (ui.*, data.*): User-facing messages, status updates, command results
- Goes to stdout/stderr
- Formatted for humans
- Respects TTY detection and color settings
- Automatically masked for secrets
Logging (log.*): System events, debugging, internal state
- Goes to log files (or /dev/stderr if configured)
- Machine-readable format
- Controlled by --logs-level flag
- Not affected by terminal capabilities

Read more in the CLI Configuration documentation (see logs section) and Global Flags for --logs-level and --logs-file options.

Real-World Examples

Before: Manual Everything

func deploy(cmd *cobra.Command, args []string) error {
    // Capability checking
    isTTY := isatty.IsTerminal(os.Stderr.Fd())

    // Using Charm Bracelet for styling
    var infoStyle, errorStyle, successStyle lipgloss.Style
    if isTTY {
        infoStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("12"))
        errorStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("9"))
        successStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("10"))
    }

    // Choose output format
    if isTTY {
        fmt.Fprintf(os.Stderr, "%s\n", infoStyle.Render("ℹ Starting deployment..."))
    } else {
        fmt.Fprintf(os.Stderr, "Starting deployment...\n")
    }

    // Do deployment
    result, err := performDeploy()
    if err != nil {
        if isTTY {
            fmt.Fprintf(os.Stderr, "%s\n", errorStyle.Render("✗ Deployment failed"))
        } else {
            fmt.Fprintf(os.Stderr, "Deployment failed\n")
        }
        return err
    }

    // Mask secrets before output
    sanitized := maskSecrets(result)

    // Output data
    json.NewEncoder(os.Stdout).Encode(sanitized)

    if isTTY {
        fmt.Fprintf(os.Stderr, "%s\n", successStyle.Render("✓ Deployment complete!"))
    } else {
        fmt.Fprintf(os.Stderr, "Deployment complete!\n")
    }

    return nil
}

After: Clean and Simple

func deploy(cmd *cobra.Command, args []string) error {
    ui.Info("Starting deployment...")

    result, err := performDeploy()
    if err != nil {
        ui.Error("Deployment failed")
        return err
    }

    data.WriteJSON(result)  // Secrets automatically masked
    ui.Success("Deployment complete!")

    return nil
}

Result: Dramatically less code, zero capability checking, automatic secret masking, perfect degradation.

Environment Support

The system automatically respects all standard conventions:

Environment Variables

NO_COLOR=1 - Disables all colors
CLICOLOR=0 - Disables colors
FORCE_COLOR=1 - Forces color even when piped
TERM=dumb - Uses plain text output
CI=true - Detects CI environment
ATMOS_FORCE_TTY=true - Forces TTY mode with sane defaults (for screenshots)
ATMOS_FORCE_COLOR=true - Forces TrueColor even for non-TTY (for screenshots)

CLI Flags

--no-color - Disables colors
--color - Enables color (only if TTY)
--force-color - Forces TrueColor even for non-TTY (for screenshots)
--force-tty - Forces TTY mode with sane defaults (for screenshots)
--redirect-stderr - Redirects UI to stdout

Terminal Detection

TTY/PTY detection via isatty
Color profile via termenv
Width via ioctl TIOCGWINSZ
CI detection via standard env vars

Testing Benefits

Testing becomes trivial:

func TestDeployCommand(t *testing.T) {
    // Setup test I/O with buffers
    stdout, stderr, cleanup := setupTestUI(t)
    defer cleanup()

    // Run command
    err := deploy(cmd, args)

    // Verify output went to correct channels
    assert.Contains(t, stderr.String(), "Deployment complete")
    assert.Contains(t, stdout.String(), `"status":"success"`)
}

No TTY mocking, no color detection stubbing, no complex test fixtures.

Migration Guide

Old Pattern (Atmos main branch before this PR)

// Old: Direct fmt.Fprintf with explicit stream access
fmt.Fprintf(os.Stderr, "Starting...\n")
fmt.Fprintf(os.Stdout, "%s\n", jsonOutput)

// Or with context retrieval
ioCtx, _ := io.NewContext()
fmt.Fprintf(ioCtx.UI(), "Starting...\n")
fmt.Fprintf(ioCtx.Data(), "%s\n", jsonOutput)

New Pattern

// New: Package-level functions with automatic I/O setup
ui.Writeln("Starting...")
data.Writeln(jsonOutput)

Available Functions

Data Output (stdout):

data.Write(text)        // Plain text
data.Writef(fmt, ...)   // Formatted
data.Writeln(text)      // With newline
data.WriteJSON(v)       // JSON
data.WriteYAML(v)       // YAML

UI Output (stderr):

ui.Write(text)             // Plain (no icon/color)
ui.Writef(fmt, ...)        // Plain formatted
ui.Writeln(text)           // Plain with newline
ui.Success(text)           // ✓ in green
ui.Error(text)             // ✗ in red
ui.Warning(text)           // ⚠ in yellow
ui.Info(text)              // ℹ in cyan
ui.Markdown(content)       // Rendered → stdout
ui.MarkdownMessage(content)// Rendered → stderr

Architecture

The magic happens through clean separation of concerns:

Developer Code
    ↓
Package Functions (data.*, ui.*)
    ↓
Formatter (color/style selection)
    ↓
Terminal (capability detection)
    ↓
I/O Layer (masking + routing)
    ↓
stdout/stderr

Each layer handles one responsibility:

Package functions - Simple API for developers
Formatter - Returns styled strings (pure, no I/O)
Terminal - Detects capabilities (TTY, color, width)
I/O Layer - Masks secrets, routes to correct stream

Performance

Zero overhead for capability detection:

Capabilities detected once at startup
Results cached for lifetime of command
No per-call TTY checks
No per-call color detection

What's Next

This foundation enables exciting future enhancements:

Progress bars - Automatic for TTY, plain for pipes
Interactive prompts - Automatic TTY detection
Spinner animations - Show in TTY, silent in CI

Try It Now

Update to the latest Atmos version and start using the new I/O system:

// Replace manual TTY checking and Lip Gloss styling
- if isatty.IsTerminal(os.Stderr.Fd()) {
-     style := lipgloss.NewStyle().Foreground(lipgloss.Color("10"))
-     fmt.Fprintf(os.Stderr, "%s\n", style.Render("✓ Done"))
- } else {
-     fmt.Fprintf(os.Stderr, "Done\n")
- }
+ ui.Success("Done")

// Replace manual JSON output
- json.NewEncoder(os.Stdout).Encode(data)
+ data.WriteJSON(data)

// Replace manual secret masking
- fmt.Println(maskSecrets(output))
+ data.Writeln(output)  // Automatic masking

Feedback

We'd love to hear your feedback on the new I/O system! Open an issue on GitHub or join the conversation in Slack.

Tags: #feature #enhancement #contributors

The Problem with Traditional CLI Output​

What Existing Solutions Don't Solve​

The Atmos Solution: Write Once, Works Everywhere​

🎨 Color Degradation​

📏 Width Adaptation​

🔍 TTY Detection​

🎭 Markdown Rendering​

🔒 Automatic Secret Masking​

🎯 Channel Separation​

📝 Logging vs Terminal Output​

Real-World Examples​

Before: Manual Everything​

After: Clean and Simple​

Environment Support​

Environment Variables​

CLI Flags​

Terminal Detection​

Testing Benefits​

Migration Guide​

Old Pattern (Atmos main branch before this PR)​

New Pattern​

Available Functions​

Architecture​

Performance​

What's Next​

Try It Now​

Feedback​