fire

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Usage

fern fire [options] [file]

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Options

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Arguments

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Examples

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Run Current Project

fern fire

Running Fern Project (linux)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Found Fern project at: /home/user/my_app
Loaded project configuration from fern.yaml
Building project for linux...
Compiling...
Build successful!

🔥 Fern Fire started!

Running /home/user/my_app/build/main...
🌿 Starting my_app...

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Run for Web Platform

fern fire -p web

Running Fern Project (web)
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Found Fern project at: /home/user/my_app
Using cached Fern web library
Compiling for web...
Build successful!

Starting local web server...
🔥 Fern Fire started (web)!

Open your browser to: http://localhost:3000/main.html
Press Ctrl+C to stop the server

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Run Single File

fern fire examples/hello.cpp

Running examples/hello.cpp (linux)
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Building single file for linux...
Compiling...
Build successful!

🔥 Fern Fire started!

Running build/hello_temp...

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Run Single File for Web

fern fire -p web main.cpp

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Platforms

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Linux (Native)

• Uses g++ compiler
• Links against system X11 libraries
• Creates executable in build/ directory
• Runs immediately after successful build

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Web (WebAssembly)

• Uses emcc compiler
• Compiles to WebAssembly (.wasm)
• Uses precompiled Fern web library for faster builds
• Starts local HTTP server on port 3000 (or configured port)
• Opens browser automatically
• Generates main.html, main.js, and main.wasm

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macOS (Experimental)

• Uses clang++ compiler
• Links against Cocoa framework
• Uses Homebrew libraries for fontconfig/freetype
• Creates native macOS executable

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Project vs Single File

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Project Mode

• Searches for fern.yaml in current directory and parents
• Builds lib/main.cpp from project root
• Uses project configuration settings
• Outputs to platform-specific directories (build/, web/build/, linux/build/)

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Single File Mode

• Compiles the specified file
• Creates temporary executable in build/ directory
• Uses minimal configuration
• Ideal for quick testing and examples

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Web Build Cache

• Precompiled Library - Fern source is compiled once to ~/.fern/cache/web/libfern_web.a
• Incremental Builds - Only your code is recompiled on subsequent builds
• Cache Invalidation - Automatically rebuilds if Fern source changes
• Manual Control - Use fern web-cache to manage the cache

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Build Output

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Linux

build/
└── main              # Executable binary

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Web

build/
├── main.html        # HTML entry point
├── main.js          # JavaScript loader
└── main.wasm        # WebAssembly binary

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Configuration

platforms:
  web:
    enabled: true
    port: 3000      # Server port (default: 8000)

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Common Workflows

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Development Loop

# Edit code
vim lib/main.cpp

# Test locally
fern fire

# Test on web
fern fire -p web

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Testing Examples

# Run an example
fern fire examples/shapes.cpp

# Run example for web
fern fire -p web examples/shapes.cpp

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Error Handling

fern fire
# Error: Not in a Fern project directory
# Run 'fern sprout <project_name>' to create a new project

fern fire
# Error: No main.cpp found in lib directory

fern fire -p web
# Error: Emscripten not found

fern fire -p web
# Port 3000 is already in use

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Web Server Features

• Auto-reload - Refresh browser to see changes after recompiling
• Graceful shutdown - Press Ctrl+C to stop server cleanly
• Port selection - Automatically finds available port if default is in use
• Browser launch - Opens browser automatically to your app
• Custom template - Uses web/template.html if present

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Performance Tips

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Web Builds

1. First build is slower (~30s) as it compiles the Fern library
2. Subsequent builds are fast (~5s) using cached library
3. Clear cache with fern web-cache clear if you update Fern source
4. Check cache with fern web-cache status to verify it’s current

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Native Builds

1. Debug builds (default) are faster to compile but slower to run
2. Production builds use fern prepare linux for optimized binaries
3. Incremental builds are automatic when supported

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Advanced Usage

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Custom Port

# Modify fern.yaml
platforms:
  web:
    port: 9000

fern fire -p web  # Uses port 9000

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Custom Web Template

<!doctype html>
<html>
<head>
    <title>My Custom App</title>
    <style>
        /* Custom styles */
    </style>
</head>
<body>
    <canvas id="canvas"></canvas>
    <script>
        var Module = { canvas: document.getElementById('canvas') };
    </script>
    {{{ SCRIPT }}}
</body>
</html>

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Related Commands

• fern prepare - Build optimized production binaries
• fern web-cache - Manage web build cache
• fern bloom - Check dependencies before building
• fern sprout - Create a new project to run