command-$tream

$treamable commands executor

A modern $ shell utility library with streaming, async iteration, and EventEmitter support, optimized for Bun runtime.

Features

• 🐚 Shell-like by Default: Commands behave exactly like running in terminal (stdout→stdout, stderr→stderr, stdin→stdin)
• 🎛️ Fully Controllable: Override default behavior with options (mirror, capture, stdin)
• 🚀 Multiple Usage Patterns: Classic await, async iteration, EventEmitter, .pipe() method, and mixed patterns
• 📡 Real-time Streaming: Process command output as it arrives, not after completion
• 🔄 Bun Optimized: Designed for Bun runtime with Node.js compatibility
• ⚡ Performance: Memory-efficient streaming prevents large buffer accumulation
• 🎯 Backward Compatible: Existing await $ syntax continues to work + Bun.$ .text() method
• 🛡️ Type Safe: Full TypeScript support (coming soon)
• 🔧 Built-in Commands: 18 essential commands work identically across platforms

Comparison with Other Libraries

Feature	command-stream	execa	cross-spawn	Bun.$	ShellJS	zx
📦 NPM Package				N/A (Built-in)
⭐ GitHub Stars	⭐ 2 (Please ⭐ us!)	⭐ 7,264	⭐ 1,149	⭐ 80,169 (Full Runtime)	⭐ 14,375	⭐ 44,569
📊 Monthly Downloads	893 (New project!)	381M	409M	N/A (Built-in)	35M	4.2M
📈 Total Downloads	Growing	6B+	5.4B	N/A (Built-in)	596M	37M
Runtime Support	✅ Bun + Node.js	✅ Node.js	✅ Node.js	🟡 Bun only	✅ Node.js	✅ Node.js
Template Literals	✅ $`cmd`	✅ $`cmd`	❌ Function calls	✅ $`cmd`	❌ Function calls	✅ $`cmd`
Real-time Streaming	✅ Live output	🟡 Limited	❌ Buffer only	❌ Buffer only	❌ Buffer only	❌ Buffer only
Synchronous Execution	✅ .sync() with events	✅ execaSync	✅ spawnSync	❌ No	✅ Sync by default	❌ No
Async Iteration	✅ for await (chunk of $.stream())	❌ No	❌ No	❌ No	❌ No	❌ No
EventEmitter Pattern	✅ .on('data', ...)	🟡 Limited events	🟡 Child process events	❌ No	❌ No	❌ No
Mixed Patterns	✅ Events + await/sync	❌ No	❌ No	❌ No	❌ No	❌ No
Bun.$ Compatibility	✅ .text() method support	❌ No	❌ No	✅ Native API	❌ No	❌ No
Shell Injection Protection	✅ Smart auto-quoting	✅ Safe by default	✅ Safe by default	✅ Built-in	🟡 Manual escaping	✅ Safe by default
Cross-platform	✅ macOS/Linux/Windows	✅ Yes	✅ Specialized cross-platform	✅ Yes	✅ Yes	✅ Yes
Performance	⚡ Fast (Bun optimized)	🐌 Moderate	⚡ Fast	⚡ Very fast	🐌 Moderate	🐌 Slow
Memory Efficiency	✅ Streaming prevents buildup	🟡 Buffers in memory	🟡 Buffers in memory	🟡 Buffers in memory	🟡 Buffers in memory	🟡 Buffers in memory
Error Handling	✅ Configurable (set -e/set +e, non-zero OK by default)	✅ Throws on error	❌ Basic (exit codes)	✅ Throws on error	✅ Configurable	✅ Throws on error
Shell Settings	✅ set -e/set +e equivalent	❌ No	❌ No	❌ No	🟡 Limited (set())	❌ No
Stdout Support	✅ Real-time streaming + events	✅ Node.js streams + interleaved	✅ Inherited/buffered	✅ Shell redirection + buffered	✅ Direct output	✅ Readable streams + .pipe.stdout
Stderr Support	✅ Real-time streaming + events	✅ Streams + interleaved output	✅ Inherited/buffered	✅ Redirection + .quiet() access	✅ Error output	✅ Readable streams + .pipe.stderr
Stdin Support	✅ string/Buffer/inherit/ignore	✅ Input/output streams	✅ Full stdio support	✅ Pipe operations	🟡 Basic	✅ Basic stdin
Built-in Commands	✅ 18 commands: cat, ls, mkdir, rm, mv, cp, touch, basename, dirname, seq, yes + all Bun.$ commands	❌ Uses system	❌ Uses system	✅ echo, cd, etc.	✅ 20+ commands: cat, ls, mkdir, rm, mv, cp, etc.	❌ Uses system
Virtual Commands Engine	✅ Revolutionary: Register JavaScript functions as shell commands with full pipeline support	❌ No custom commands	❌ No custom commands	❌ No extensibility	❌ No custom commands	❌ No custom commands
Pipeline/Piping Support	✅ Advanced: System + Built-ins + Virtual + Mixed + .pipe() method	✅ Programmatic .pipe() + multi-destination	❌ No piping	✅ Standard shell piping	✅ Shell piping + .to() method	✅ Shell piping + .pipe() method
Bundle Size	📦 ~20KB gzipped	📦 ~400KB+ (packagephobia)	📦 ~2KB gzipped	🎯 0KB (built-in)	📦 ~15KB gzipped	📦 ~50KB+ (estimated)
Signal Handling	✅ Advanced SIGINT/SIGTERM forwarding with cleanup	🟡 Basic	✅ Excellent cross-platform	🟡 Basic	🟡 Basic	🟡 Basic
Process Management	✅ Robust child process lifecycle with proper termination	✅ Good	✅ Excellent spawn wrapper	❌ Basic	🟡 Limited	🟡 Limited
Debug Tracing	✅ Comprehensive VERBOSE logging for CI/debugging	🟡 Limited	❌ No	❌ No	🟡 Basic	❌ No
Test Coverage	✅ 518+ tests, 1165+ assertions	✅ Excellent	✅ Good	🟡 Good coverage	✅ Good	🟡 Good
CI Reliability	✅ Platform-specific handling (macOS/Ubuntu)	✅ Good	✅ Excellent	🟡 Basic	✅ Good	🟡 Basic
Documentation	✅ Comprehensive examples + guides	✅ Excellent	🟡 Basic	✅ Good	✅ Good	🟡 Limited
TypeScript	🔄 Coming soon	✅ Full support	✅ Built-in	✅ Built-in	🟡 Community types	✅ Full support
License	✅ Unlicense (Public Domain)	🟡 MIT	🟡 MIT	🟡 MIT (+ LGPL dependencies)	🟡 BSD-3-Clause	🟡 Apache 2.0

📊 Popularity & Adoption:

• ⭐ GitHub Stars: Bun: 80,169 • zx: 44,569 • ShellJS: 14,375 • execa: 7,264 • cross-spawn: 1,149 • command-stream: 2 ⭐ us!
• 📈 Total Downloads: execa: 6B+ • cross-spawn: 5.4B • ShellJS: 596M • zx: 37M • command-stream: Growing
• 📊 Monthly Downloads: cross-spawn: 409M • execa: 381M • ShellJS: 35M • zx: 4.2M • command-stream: 893 (growing!)

⭐ Help Us Grow! If command-stream's revolutionary virtual commands and advanced streaming capabilities help your project, please star us on GitHub to help the project grow!

Why Choose command-stream?

• 🆓 Truly Free: Unlicense (Public Domain) - No restrictions, no attribution required, use however you want
• 🚀 Revolutionary Virtual Commands: World's first fully customizable virtual commands engine - register JavaScript functions as shell commands!
• 🔗 Advanced Pipeline System: Only library where virtual commands work seamlessly in pipelines with built-ins and system commands
• 🔧 Built-in Commands: 18 essential commands work identically across all platforms - no system dependencies!
• 📡 Real-time Processing: Only library with true streaming and async iteration
• 🔄 Flexible Patterns: Multiple usage patterns (await, events, iteration, mixed)
• 🐚 Shell Replacement: Dynamic error handling with set -e/set +e equivalents for .sh file replacement
• ⚡ Bun Optimized: Designed for Bun with Node.js fallback compatibility
• 💾 Memory Efficient: Streaming prevents large buffer accumulation
• 🛡️ Production Ready: 518+ tests, 1165+ assertions with comprehensive coverage including CI reliability
• 🎯 Advanced Signal Handling: Robust SIGINT/SIGTERM forwarding with proper child process cleanup
• 🔍 Debug-Friendly: Comprehensive VERBOSE tracing for CI debugging and troubleshooting

Built-in Commands (🚀 NEW!)

command-stream now includes 18 built-in commands that work identically to their bash/sh counterparts, providing true cross-platform shell scripting without system dependencies:

📁 File System Commands

• cat - Read and display file contents
• ls - List directory contents (supports -l, -a, -A)
• mkdir - Create directories (supports -p recursive)
• rm - Remove files/directories (supports -r, -f)
• mv - Move/rename files and directories
• cp - Copy files/directories (supports -r recursive)
• touch - Create files or update timestamps

🔧 Utility Commands

• basename - Extract filename from path
• dirname - Extract directory from path
• seq - Generate number sequences
• yes - Output string repeatedly (streaming)

⚡ System Commands

• cd - Change directory
• pwd - Print working directory
• echo - Print arguments (supports -n)
• sleep - Wait for specified time
• true/false - Success/failure commands
• which - Locate commands
• exit - Exit with code
• env - Print environment variables
• test - File condition testing

✨ Key Advantages

• 🌍 Cross-Platform: Works identically on Windows, macOS, and Linux
• 🚀 Performance: No system calls - pure JavaScript execution
• 🔄 Pipeline Support: All commands work in pipelines and virtual command chains
• ⚙️ Option Aware: Commands respect cwd, env, and other options
• 🛡️ Safe by Default: Proper error handling and safety checks (e.g., rm requires -r for directories)
• 📝 Bash Compatible: Error messages and behavior match bash/sh exactly

import { $ } from 'command-stream';

// All these work without any system dependencies!
await $`mkdir -p project/src`;
await $`touch project/src/index.js`;
await $`echo "console.log('Hello!');" > project/src/index.js`;
await $`ls -la project/src`;
await $`cat project/src/index.js`;
await $`cp -r project project-backup`;
await $`rm -r project-backup`;

// Mix built-ins with pipelines and virtual commands
await $`seq 1 5 | cat > numbers.txt`;
await $`basename /path/to/file.txt .txt`; // → "file"

Installation

# Using npm
npm install command-stream

# Using bun
bun add command-stream

Smart Quoting & Security

Command-stream provides intelligent auto-quoting to protect against shell injection while avoiding unnecessary quotes for safe strings:

Smart Quoting Behavior

import { $ } from 'command-stream';

// Safe strings are NOT quoted (performance optimization)
await $`echo ${name}`;           // name = "hello" → echo hello
await $`${cmd} --version`;       // cmd = "/usr/bin/node" → /usr/bin/node --version

// Dangerous strings are automatically quoted for safety
await $`echo ${userInput}`;      // userInput = "test; rm -rf /" → echo 'test; rm -rf /'
await $`echo ${pathWithSpaces}`; // pathWithSpaces = "/my path/file" → echo '/my path/file'

// Special characters that trigger auto-quoting:
// Spaces, $, ;, |, &, >, <, `, *, ?, [, ], {, }, (, ), !, #, and others

// User-provided quotes are preserved
const quotedPath = "'/path with spaces/file'";
await $`cat ${quotedPath}`;      // → cat '/path with spaces/file' (no double-quoting!)

const doubleQuoted = '"/path with spaces/file"';
await $`cat ${doubleQuoted}`;    // → cat '"/path with spaces/file"' (preserves intent)

Shell Injection Protection

All interpolated values are automatically secured:

// ✅ SAFE - All these injection attempts are neutralized
const dangerous = "'; rm -rf /; echo '";
await $`echo ${dangerous}`;      // → echo ''\'' rm -rf /; echo '\'''

const cmdSubstitution = "$(whoami)";
await $`echo ${cmdSubstitution}`; // → echo '$(whoami)' (literal text, not executed)

const varExpansion = "$HOME";
await $`echo ${varExpansion}`;   // → echo '$HOME' (literal text, not expanded)

// ✅ SAFE - Even complex injection attempts
const complex = "`cat /etc/passwd`";
await $`echo ${complex}`;        // → echo '`cat /etc/passwd`' (literal text)

Usage Patterns

Classic Await (Backward Compatible)

import { $ } from 'command-stream';

const result = await $`ls -la`;
console.log(result.stdout);
console.log(result.code); // exit code

Custom Options with $({ options }) Syntax (NEW!)

import { $ } from 'command-stream';

// Create a $ with custom options
const $silent = $({ mirror: false, capture: true });
const result = await $silent`echo "quiet operation"`;

// Options for stdin handling
const $withInput = $({ stdin: 'input data\n' });
await $withInput`cat`; // Pipes the input to cat

// Custom environment variables
const $withEnv = $({ env: { ...process.env, MY_VAR: 'value' } });
await $withEnv`printenv MY_VAR`; // Prints: value

// Custom working directory
const $inTmp = $({ cwd: '/tmp' });
await $inTmp`pwd`; // Prints: /tmp

// Interactive mode for TTY commands (requires TTY environment)
const $interactive = $({ interactive: true });
await $interactive`vim myfile.txt`; // Full TTY access for editor
await $interactive`less README.md`; // Proper pager interaction

// Combine multiple options
const $custom = $({
  stdin: 'test data',
  mirror: false,
  capture: true,
  cwd: '/tmp'
});
await $custom`cat > output.txt`; // Writes to /tmp/output.txt silently

// Reusable configurations
const $prod = $({ env: { NODE_ENV: 'production' }, capture: true });
await $prod`npm start`;
await $prod`npm test`;

Execution Control (NEW!)

import { $ } from 'command-stream';

// Commands don't auto-start when created
const cmd = $`echo "hello"`;

// Three ways to start execution:

// 1. Explicit start with options
cmd.start();                    // Default async mode
cmd.start({ mode: 'async' });   // Explicitly async
cmd.start({ mode: 'sync' });    // Synchronous execution

// 2. Convenience methods
cmd.async();  // Same as start({ mode: 'async' })
cmd.sync();   // Same as start({ mode: 'sync' })

// 3. Auto-start by awaiting (always async)
await cmd;    // Auto-starts in async mode

// Event handlers can be attached before starting
const process = $`long-command`
  .on('data', chunk => console.log('Received:', chunk))
  .on('end', result => console.log('Done!'));

// Start whenever you're ready
process.start();

Synchronous Execution

import { $ } from 'command-stream';

// Use .sync() for blocking execution
const result = $`echo "hello"`.sync();
console.log(result.stdout); // "hello\n"

// Events still work but are batched after completion
$`echo "world"`
  .on('end', result => console.log('Done:', result))
  .sync();

Async Iteration (Real-time Streaming)

import { $ } from 'command-stream';

for await (const chunk of $`long-running-command`.stream()) {
  if (chunk.type === 'stdout') {
    console.log('Real-time output:', chunk.data.toString());
  }
}

EventEmitter Pattern (Event-driven)

import { $ } from 'command-stream';

// Attach event handlers then start execution
$`command`
  .on('data', chunk => {
    if (chunk.type === 'stdout') {
      console.log('Stdout:', chunk.data.toString());
    }
  })
  .on('stderr', chunk => console.log('Stderr:', chunk))
  .on('end', result => console.log('Done:', result))
  .on('exit', code => console.log('Exit code:', code))
  .start(); // Explicitly start the command

// Or auto-start by awaiting
const cmd = $`another-command`
  .on('data', chunk => console.log(chunk));
await cmd; // Auto-starts in async mode

Mixed Pattern (Best of Both Worlds)

import { $ } from 'command-stream';

// Async mode - events fire in real-time
const process = $`streaming-command`;
process.on('data', chunk => {
  processRealTimeData(chunk);
});
const result = await process;
console.log('Final output:', result.stdout);

// Sync mode - events fire after completion (batched)
const syncCmd = $`another-command`;
syncCmd.on('end', result => {
  console.log('Completed with:', result.stdout);
});
const syncResult = syncCmd.sync();

Streaming Interfaces

Advanced streaming interfaces for fine-grained process control:

import { $ } from 'command-stream';

// 🎯 STDIN CONTROL: Send data to interactive commands (real-time)
const grepCmd = $`grep "important"`;
const stdin = await grepCmd.streams.stdin; // Available immediately

stdin.write('ignore this line\n');
stdin.write('important message\n');
stdin.write('skip this too\n');
stdin.end();

const result = await grepCmd;
console.log(result.stdout); // "important message\n"

// 🔧 BINARY DATA: Access raw buffers (after command finishes)
const cmd = $`echo "Hello World"`;
const buffer = await cmd.buffers.stdout; // Complete snapshot
console.log(buffer.length); // 12

// 📝 TEXT DATA: Access as strings (after command finishes)
const textCmd = $`echo "Hello World"`;
const text = await textCmd.strings.stdout; // Complete snapshot
console.log(text.trim()); // "Hello World"

// ⚡ PROCESS CONTROL: Kill commands that ignore stdin
const pingCmd = $`ping google.com`;

// Some commands ignore stdin input
const pingStdin = await pingCmd.streams.stdin;
if (pingStdin) {
  pingStdin.write('q\n'); // ping ignores this
}

// Use kill() for forceful termination
setTimeout(() => pingCmd.kill(), 2000);
const pingResult = await pingCmd;
console.log('Ping stopped with code:', pingResult.code); // 143 (SIGTERM)

// 🔄 MIXED STDOUT/STDERR: Handle both streams (complete snapshots)
const mixedCmd = $`sh -c 'echo "out" && echo "err" >&2'`;
const [stdout, stderr] = await Promise.all([
  mixedCmd.strings.stdout, // Available after finish
  mixedCmd.strings.stderr  // Available after finish
]);
console.log('Out:', stdout.trim()); // "out"  
console.log('Err:', stderr.trim()); // "err"

// 🏃‍♂️ AUTO-START: Streams auto-start processes when accessed
const cmd = $`echo "test"`;
console.log('Started?', cmd.started); // false

const output = await cmd.streams.stdout; // Auto-starts, immediate access
console.log('Started?', cmd.started); // true

// 🔙 BACKWARD COMPATIBLE: Traditional await still works
const traditional = await $`echo "still works"`;
console.log(traditional.stdout); // "still works\n"

Key Features:

• command.streams.stdin/stdout/stderr - Direct access to Node.js streams
• command.buffers.stdin/stdout/stderr - Binary data as Buffer objects
• command.strings.stdin/stdout/stderr - Text data as strings
• command.kill() - Forceful process termination
• Auto-start behavior: Process starts only when accessing stream properties
• Perfect for: Interactive commands (grep, sort, bc), data processing, real-time control
• Network commands (ping, wget) ignore stdin → Use kill() method instead

🚀 Streams vs Buffers/Strings:

• streams.* - Available immediately when command starts, for real-time interaction
• buffers.* & strings.* - Complete snapshots available only after command finishes

Shell Replacement (.sh → .mjs)

Replace bash scripts with JavaScript while keeping shell semantics:

import { $, shell, set, unset } from 'command-stream';

// set -e equivalent: exit on any error
shell.errexit(true);

await $`mkdir -p build`;
await $`npm run build`;

// set +e equivalent: allow errors (like bash)
shell.errexit(false);
const cleanup = await $`rm -rf temp`; // Won't throw if fails

// set -e again for critical operations  
shell.errexit(true);
await $`cp -r build/* deploy/`;

// Other bash-like settings
shell.verbose(true);  // set -v: print commands
shell.xtrace(true);   // set -x: trace execution

// Or use the bash-style API
set('e');    // set -e
unset('e');  // set +e
set('x');    // set -x
set('verbose'); // Long form also supported

Cross-Platform File Operations (Built-in Commands)

Replace system-dependent operations with built-in commands that work identically everywhere:

import { $ } from 'command-stream';

// File system operations work on Windows, macOS, and Linux identically
await $`mkdir -p project/src project/tests`;
await $`touch project/src/index.js project/tests/test.js`;

// List files with details
const files = await $`ls -la project/src`;
console.log(files.stdout);

// Copy and move operations
await $`cp project/src/index.js project/src/backup.js`;
await $`mv project/src/backup.js project/backup.js`;

// File content operations
await $`echo "export default 'Hello World';" > project/src/index.js`;
const content = await $`cat project/src/index.js`;
console.log(content.stdout);

// Path operations
const filename = await $`basename project/src/index.js .js`; // → "index"
const directory = await $`dirname project/src/index.js`;     // → "project/src"

// Generate sequences and process them
await $`seq 1 10 | cat > numbers.txt`;
const numbers = await $`cat numbers.txt`;

// Cleanup
await $`rm -r project numbers.txt`;

Virtual Commands (Extensible Shell)

Create custom commands that work seamlessly alongside built-ins:

import { $, register, unregister, listCommands } from 'command-stream';

// Register a custom command
register('greet', async ({ args, stdin }) => {
  const name = args[0] || 'World';
  return { stdout: `Hello, ${name}!\n`, code: 0 };
});

// Use it like any other command
await $`greet Alice`;                    // → "Hello, Alice!"
await $`echo "Bob" | greet`;             // → "Hello, Bob!"

// Streaming virtual commands with async generators
register('countdown', async function* ({ args }) {
  const start = parseInt(args[0] || 5);
  for (let i = start; i >= 0; i--) {
    yield `${i}\n`;
    await new Promise(r => setTimeout(r, 1000));
  }
});

// Use in pipelines with built-ins
await $`countdown 3 | cat > countdown.txt`;

// Virtual commands work in all patterns
for await (const chunk of $`countdown 3`.stream()) {
  console.log('Countdown:', chunk.data.toString().trim());
}

// Management functions
console.log(listCommands());  // List all registered commands
unregister('greet');          // Remove custom commands

🔥 Why Virtual Commands Are Revolutionary

No other shell library offers this level of extensibility:

• 🚫 Bun.$: Fixed set of built-in commands, no extensibility API
• 🚫 execa: Transform/pipeline system, but no custom commands
• 🚫 zx: JavaScript functions only, no shell command integration

command-stream breaks the barrier between JavaScript functions and shell commands:

// ❌ Other libraries: Choose JavaScript OR shell
await execa('node', ['script.js']);  // execa: separate processes
await $`node script.js`;             // zx: shell commands only

// ✅ command-stream: JavaScript functions AS shell commands  
register('deploy', async ({ args }) => {
  const env = args[0] || 'staging';
  await deployToEnvironment(env);
  return { stdout: `Deployed to ${env}!\n`, code: 0 };
});

await $`deploy production`;           // JavaScript function as shell command!
await $`deploy staging | tee log.txt`; // Works in pipelines!

Unique capabilities:

• Seamless Integration: Virtual commands work exactly like built-ins
• Pipeline Support: Full stdin/stdout passing between virtual and system commands
• Streaming: Async generators for real-time output
• Dynamic Registration: Add/remove commands at runtime
• Option Awareness: Virtual commands respect cwd, env, etc.

🔗 Advanced Pipeline Support

command-stream offers the most advanced piping system in the JavaScript ecosystem:

Shell-Style Piping (Traditional)

import { $, register } from 'command-stream';

// ✅ Standard shell piping (like all libraries)
await $`echo "hello world" | wc -w`;  // → "2"

// ✅ Built-in to built-in piping  
await $`seq 1 5 | cat > numbers.txt`;

// ✅ System to built-in piping
await $`git log --oneline | head -n 5`;

// 🚀 UNIQUE: Virtual command piping
register('uppercase', async ({ args, stdin }) => {
  return { stdout: stdin.toUpperCase(), code: 0 };
});

register('reverse', async ({ args, stdin }) => {
  return { stdout: stdin.split('').reverse().join(''), code: 0 };
});

// ✅ Built-in to virtual piping
await $`echo "hello" | uppercase`;  // → "HELLO"

// ✅ Virtual to virtual piping  
await $`echo "hello" | uppercase | reverse`;  // → "OLLEH"

// ✅ Mixed pipelines (system + built-in + virtual)
await $`git log --oneline | head -n 3 | uppercase | cat > LOG.txt`;

// ✅ Complex multi-stage pipelines
await $`find . -name "*.js" | head -n 10 | basename | sort | uniq`;

🚀 Programmatic .pipe() Method (NEW!)

World's first shell library with full .pipe() method support for virtual commands:

import { $, register } from 'command-stream';

// ✅ Basic programmatic piping
const result = await $`echo "hello"`.pipe($`echo "World: $(cat)"`);

// 🌟 Virtual command chaining
register('add-prefix', async ({ args, stdin }) => {
  const prefix = args[0] || 'PREFIX:';
  return { stdout: `${prefix} ${stdin.trim()}\n`, code: 0 };
});

register('add-suffix', async ({ args, stdin }) => {
  const suffix = args[0] || 'SUFFIX';
  return { stdout: `${stdin.trim()} ${suffix}\n`, code: 0 };
});

// ✅ Chain virtual commands with .pipe()
const result = await $`echo "Hello"`
  .pipe($`add-prefix "[PROCESSED]"`)
  .pipe($`add-suffix "!!!"`);
// → "[PROCESSED] Hello !!!"

// ✅ Mix with built-in commands
const fileData = await $`cat large-file.txt`
  .pipe($`head -n 100`)
  .pipe($`add-prefix "Line:"`);

// ✅ Error handling in pipelines
try {
  const result = await $`cat nonexistent.txt`.pipe($`add-prefix "Data:"`);
} catch (error) {
  // Source error propagates - destination never executes
  console.log('File not found, pipeline stopped');
}

// ✅ Complex data processing
register('json-parse', async ({ args, stdin }) => {
  try {
    const data = JSON.parse(stdin);
    return { stdout: JSON.stringify(data, null, 2), code: 0 };
  } catch (error) {
    return { stdout: '', stderr: `JSON Error: ${error.message}`, code: 1 };
  }
});

register('extract-field', async ({ args, stdin }) => {
  const field = args[0];
  try {
    const data = JSON.parse(stdin);
    const value = data[field] || 'null';
    return { stdout: `${value}\n`, code: 0 };
  } catch (error) {
    return { stdout: '', stderr: `Extract Error: ${error.message}`, code: 1 };
  }
});

// Real-world API processing pipeline
const userName = await $`curl -s https://api.github.com/users/octocat`
  .pipe($`json-parse`)
  .pipe($`extract-field name`);
// → "The Octocat"

// Cleanup
unregister('add-prefix');
unregister('add-suffix');
unregister('json-parse');
unregister('extract-field');

🆚 How We Compare

Library	Pipeline Types	Custom Commands in Pipes	.pipe() Method	Real-time Streaming
command-stream	✅ System + Built-ins + Virtual + Mixed	✅ Full support	✅ Full virtual command support	✅ Yes
Bun.$	✅ System + Built-ins	❌ No custom commands	❌ No .pipe() method	❌ No
execa	✅ Programmatic .pipe()	❌ No shell integration	✅ Basic process piping	🟡 Limited
zx	✅ Shell piping + .pipe()	❌ No custom commands	✅ Stream piping only	❌ No

🎯 Unique Advantages:

• Virtual commands work seamlessly in both shell pipes AND .pipe() method - no other library can do this
• Mixed pipeline types - combine system, built-in, and virtual commands freely in both syntaxes
• Real-time streaming through virtual command pipelines
• Full stdin/stdout passing between all command types
• Dual piping syntax - use shell | OR programmatic .pipe() interchangeably

Default Behavior: Shell-like with Programmatic Control

command-stream behaves exactly like running commands in your shell by default:

import { $ } from 'command-stream';

// This command will:
// 1. Print "Hello" to your terminal (stdout→stdout)
// 2. Print "Error!" to your terminal (stderr→stderr) 
// 3. Capture both outputs for programmatic access
const result = await $`sh -c "echo 'Hello'; echo 'Error!' >&2"`;

console.log('Captured stdout:', result.stdout); // "Hello\n"
console.log('Captured stderr:', result.stderr); // "Error!\n"
console.log('Exit code:', result.code);         // 0

Key Default Options:

• mirror: true - Live output to terminal (like shell)
• capture: true - Capture output for later use (unlike shell)
• stdin: 'inherit' - Inherit stdin from parent process

Fully Controllable:

import { $, create, sh } from 'command-stream';

// Disable terminal output but still capture
const result = await sh('echo "silent"', { mirror: false });

// Custom stdin input  
const custom = await sh('cat', { stdin: "custom input" });

// Create custom $ with different defaults
const quiet$ = create({ mirror: false });
await quiet$`echo "silent"`; // Won't print to terminal

// Disable both mirroring and capturing for performance
await sh('make build', { mirror: false, capture: false });

This gives you the best of both worlds: shell-like behavior by default, but with full programmatic control and real-time streaming capabilities.

Real-world Examples

Log File Streaming with Session ID Extraction

import { $ } from 'command-stream';
import { appendFileSync, writeFileSync } from 'fs';

let sessionId = null;
let logFile = null;

for await (const chunk of $`your-streaming-command`.stream()) {
  if (chunk.type === 'stdout') {
    const data = chunk.data.toString();
    
    // Extract session ID from output
    if (!sessionId && data.includes('session_id')) {
      try {
        const parsed = JSON.parse(data);
        sessionId = parsed.session_id;
        logFile = `${sessionId}.log`;
        console.log(`Session ID: ${sessionId}`);
      } catch (e) {
        // Handle JSON parse errors
      }
    }
    
    // Write to log file in real-time
    if (logFile) {
      appendFileSync(logFile, data);
    }
  }
}

Progress Monitoring

import { $ } from 'command-stream';

let progress = 0;

$`download-large-file`
  .on('stdout', (chunk) => {
    const output = chunk.toString();
    if (output.includes('Progress:')) {
      progress = parseProgress(output);
      updateProgressBar(progress);
    }
  })
  .on('end', (result) => {
    console.log('Download completed!');
  });

API Reference

ProcessRunner Class

The enhanced $ function returns a ProcessRunner instance that extends EventEmitter.

Events

• data: Emitted for each chunk with {type: 'stdout'|'stderr', data: Buffer}
• stdout: Emitted for stdout chunks (Buffer)
• stderr: Emitted for stderr chunks (Buffer)
• end: Emitted when process completes with final result object
• exit: Emitted with exit code

Methods

• start(options): Explicitly start command execution
  • options.mode: 'async' (default) or 'sync' - execution mode
• async(): Shortcut for start({ mode: 'async' }) - start async execution
• sync(): Shortcut for start({ mode: 'sync' }) - execute synchronously (blocks until completion)
• stream(): Returns an async iterator for real-time chunk processing
• pipe(destination): Programmatically pipe output to another command (returns new ProcessRunner)
• then(), catch(), finally(): Promise interface for await support (auto-starts in async mode)

Properties

• stdout: Direct access to child process stdout stream
• stderr: Direct access to child process stderr stream
• stdin: Direct access to child process stdin stream

Default Options

By default, command-stream behaves like running commands in the shell:

{
  mirror: true,        // Live output to terminal (stdout→stdout, stderr→stderr)
  capture: true,       // Capture output for programmatic access
  stdin: 'inherit',    // Inherit stdin from parent process
  interactive: false   // Explicitly request TTY forwarding for interactive commands
}

Option Details:

• mirror: boolean - Whether to pipe output to terminal in real-time
• capture: boolean - Whether to capture output in result object
• stdin: 'inherit' | 'ignore' | string | Buffer - How to handle stdin
• interactive: boolean - Enable TTY forwarding for interactive commands (requires stdin: 'inherit' and TTY environment)
• cwd: string - Working directory for command
• env: object - Environment variables

Override defaults:

• Use $({ options }) syntax for one-off configurations with template literals
• Use sh(command, options) for one-off overrides with string commands
• Use create(defaultOptions) to create custom $ with different defaults

Shell Settings API

Control shell behavior like bash set/unset commands:

Functions

• shell.errexit(boolean): Enable/disable exit-on-error (like set ±e)
• shell.verbose(boolean): Enable/disable command printing (like set ±v)
• shell.xtrace(boolean): Enable/disable execution tracing (like set ±x)
• set(option): Enable shell option ('e', 'v', 'x', or long names)
• unset(option): Disable shell option
• shell.settings(): Get current settings object

Error Handling Modes

import { $, shell } from 'command-stream';

// ✅ Default behavior: Commands don't throw on non-zero exit
const result = await $`ls nonexistent-file`; // Won't throw
console.log(result.code); // → 2 (non-zero, but no exception)

// ✅ Enable errexit: Commands throw on non-zero exit
shell.errexit(true);
try {
  await $`ls nonexistent-file`; // Throws error
} catch (error) {
  console.log('Command failed:', error.code); // → 2
}

// ✅ Disable errexit: Back to non-throwing behavior
shell.errexit(false);
await $`ls nonexistent-file`; // Won't throw, returns result with code 2

// ✅ One-time override without changing global settings
try {
  const result = await $`ls nonexistent-file`;
  if (result.code !== 0) {
    throw new Error(`Command failed with code ${result.code}`);
  }
} catch (error) {
  console.log('Manual error handling');
}

Virtual Commands API

Control and extend the command system with custom JavaScript functions:

Functions

• register(name, handler): Register a virtual command
  • name: Command name (string)
  • handler: Function or async generator (args, stdin, options) => result
• unregister(name): Remove a virtual command
• listCommands(): Get array of all registered command names
• enableVirtualCommands(): Enable virtual command processing
• disableVirtualCommands(): Disable virtual commands (use system commands only)

Advanced Virtual Command Features

import { $, register } from 'command-stream';

// ✅ Cancellation support with AbortController
register('cancellable', async function* ({ args, stdin, abortSignal }) {
  for (let i = 0; i < 10; i++) {
    if (abortSignal?.aborted) {
      break; // Proper cancellation handling
    }
    yield `Count: ${i}\n`;
    await new Promise(resolve => setTimeout(resolve, 1000));
  }
});

// ✅ Access to all process options
// All original options (built-in + custom) are available in the 'options' object
// Common options like cwd, env are also available at top level for convenience
// Runtime additions: isCancelled function, abortSignal
register('debug-info', async ({ args, stdin, cwd, env, options, isCancelled }) => {
  return {
    stdout: JSON.stringify({
      args,
      cwd,  // Available at top level for convenience
      env: Object.keys(env || {}),  // Available at top level for convenience
      stdinLength: stdin?.length || 0,
      allOptions: options,  // All original options (built-in + custom)
      mirror: options.mirror,  // Built-in option from options object
      capture: options.capture,  // Built-in option from options object
      customOption: options.customOption || 'not provided',  // Custom option
      isCancelledAvailable: typeof isCancelled === 'function'
    }, null, 2),
    code: 0
  };
});

// ✅ Error handling and non-zero exit codes
register('maybe-fail', async ({ args }) => {
  if (Math.random() > 0.5) {
    return {
      stdout: 'Success!\n',
      code: 0
    };
  } else {
    return {
      stdout: '',
      stderr: 'Random failure occurred\n',
      code: 1
    };
  }
});

// ✅ Example: User options flow through to virtual commands
register('show-options', async ({ args, stdin, options, cwd }) => {
  return {
    stdout: `Custom: ${options.customValue || 'none'}, CWD: ${cwd || options.cwd || 'default'}\n`,
    code: 0
  };
});

// Usage example showing options passed to virtual command:
const result = await $({ customValue: 'hello world', cwd: '/tmp' })`show-options`;
console.log(result.stdout); // Output: Custom: hello world, CWD: /tmp

Handler Function Signature

// Regular async function
async function handler({ args, stdin, abortSignal, cwd, env, options, isCancelled }) {
  // All original options available in 'options': options.mirror, options.capture, options.customValue, etc.
  // Common options like cwd, env also available at top level for convenience
  return {
    code: 0,           // Exit code (number)
    stdout: "output",  // Standard output (string)
    stderr: "",        // Standard error (string)
  };
}

// Async generator for streaming
async function streamingHandler({ args, stdin, abortSignal, cwd, env, options, isCancelled }) {
  // Access both built-in and custom options from 'options' object
  if (options.customFlag) {
    yield "custom behavior\n";
  }
  yield "chunk1\n";
  yield "chunk2\n";
}

Built-in Commands

18 cross-platform commands that work identically everywhere:

File System: cat, ls, mkdir, rm, mv, cp, touch
Utilities: basename, dirname, seq, yes
System: cd, pwd, echo, sleep, true, false, which, exit, env, test

All built-in commands support:

• Standard flags (e.g., ls -la, mkdir -p, rm -rf)
• Pipeline operations
• Option awareness (cwd, env, etc.)
• Bash-compatible error messages and exit codes

Supported Options

• 'e' / 'errexit': Exit on command failure
• 'v' / 'verbose': Print commands before execution
• 'x' / 'xtrace': Trace command execution with + prefix
• 'u' / 'nounset': Error on undefined variables (planned)
• 'pipefail': Pipe failure detection (planned)

Result Object

{
  code: number,        // Exit code
  stdout: string,      // Complete stdout output
  stderr: string,      // Complete stderr output
  stdin: string,       // Input sent to process
  child: ChildProcess, // Original child process object
  async text()         // Bun.$ compatibility method - returns stdout as string
}

.text() Method (Bun.$ Compatibility)

For compatibility with Bun.$, all result objects include an async .text() method:

import { $ } from 'command-stream';

// Both sync and async execution support .text()
const result1 = await $`echo "hello world"`;
const text1 = await result1.text(); // "hello world\n"

const result2 = $`echo "sync example"`.sync();  
const text2 = await result2.text(); // "sync example\n"

// .text() is equivalent to accessing .stdout
expect(await result.text()).toBe(result.stdout);

// Works with built-in commands
const result3 = await $`seq 1 3`;
const text3 = await result3.text(); // "1\n2\n3\n"

// Works with .pipe() method
const result4 = await $`echo "pipe test"`.pipe($`cat`);
const text4 = await result4.text(); // "pipe test\n"

Signal Handling (CTRL+C Support)

The library provides advanced CTRL+C handling that properly manages signals across different scenarios:

How It Works

1. Smart Signal Forwarding: CTRL+C is forwarded only when child processes are active
2. User Handler Preservation: When no children are running, your custom SIGINT handlers work normally
3. Process Groups: Child processes use detached spawning for proper signal isolation
4. TTY Mode Support: Raw TTY mode is properly managed and restored on interruption
5. Graceful Termination: Uses SIGTERM → SIGKILL escalation for robust process cleanup
6. Exit Code Standards: Proper signal exit codes (130 for SIGINT, 143 for SIGTERM)

Advanced Signal Behavior

// ✅ Smart signal handling - only interferes when necessary
import { $ } from 'command-stream';

// Case 1: No children active - your handlers work normally  
process.on('SIGINT', () => {
  console.log('My custom handler runs!');
  process.exit(42); // Custom exit code
});
// Press CTRL+C → Your handler runs, exits with code 42

// Case 2: Children active - automatic forwarding
await $`ping 8.8.8.8`; // Press CTRL+C → Forwards to ping, exits with code 130

// Case 3: Multiple processes - all interrupted
await Promise.all([
  $`sleep 100`,
  $`ping google.com`  
]); // Press CTRL+C → All processes terminated, exits with code 130

Examples

// Long-running command that can be interrupted with CTRL+C
try {
  await $`ping 8.8.8.8`;  // Press CTRL+C to stop
} catch (error) {
  console.log('Command interrupted:', error.code); // Exit code 130 (SIGINT)
}

// Multiple concurrent processes - CTRL+C stops all
try {
  await Promise.all([
    $`sleep 100`,
    $`ping google.com`,
    $`tail -f /var/log/system.log`
  ]);
} catch (error) {
  // All processes are terminated when you press CTRL+C
}

// Works with streaming patterns too
try {
  for await (const chunk of $`ping 8.8.8.8`.stream()) {
    console.log(chunk);
    // Press CTRL+C to break the loop and stop the process
  }
} catch (error) {
  console.log('Streaming interrupted');
}

Signal Handling Behavior

• 🎯 Smart Detection: Only forwards CTRL+C when child processes are active
• 🛡️ Non-Interference: Preserves user SIGINT handlers when no children running
• ⚡ Interactive Commands: Use interactive: true option for commands like vim, less, top to enable proper TTY forwarding and signal handling
• 🔄 Process Groups: Detached spawning ensures proper signal isolation
• 🧹 TTY Cleanup: Raw terminal mode properly restored on interruption
• 📊 Standard Exit Codes:
  • 130 - SIGINT interruption (CTRL+C)
  • 143 - SIGTERM termination (programmatic kill)
  • 137 - SIGKILL force termination

Command Resolution Priority

// Understanding how commands are resolved:

// 1. Virtual Commands (highest priority)
register('echo', () => ({ stdout: 'virtual!\n', code: 0 }));
await $`echo test`; // → "virtual!"

// 2. Built-in Commands (if no virtual match)  
unregister('echo');
await $`echo test`; // → Uses built-in echo

// 3. System Commands (if no built-in/virtual match)
await $`unknown-command`; // → Uses system PATH lookup

// 4. Virtual Bypass (special case)
await $({ stdin: 'data' })`sleep 1`; // Bypasses virtual sleep, uses system sleep

Execution Patterns Deep Dive

When to Use Different Patterns

import { $ } from 'command-stream';

// ✅ Use await for simple command execution
const result = await $`ls -la`;

// ✅ Use .sync() when you need blocking execution with events
const syncCmd = $`build-script`
  .on('stdout', chunk => updateProgress(chunk))
  .sync(); // Events fire after completion

// ✅ Use .start() for non-blocking execution with real-time events  
const asyncCmd = $`long-running-server`
  .on('stdout', chunk => logOutput(chunk))
  .start(); // Events fire in real-time

// ✅ Use .stream() for processing large outputs efficiently
for await (const chunk of $`generate-big-file`.stream()) {
  processChunkInRealTime(chunk);
} // Memory efficient - processes chunks as they arrive

// ✅ Use EventEmitter pattern for complex workflows
$`deployment-script`
  .on('stdout', chunk => {
    if (chunk.toString().includes('ERROR')) {
      handleError(chunk);
    }
  })
  .on('stderr', chunk => logError(chunk))
  .on('end', result => {
    if (result.code === 0) {
      notifySuccess();
    }
  })
  .start();

Performance Considerations

// 🚀 Memory Efficient: For large outputs, use streaming
for await (const chunk of $`cat huge-file.log`.stream()) {
  processChunk(chunk); // Processes incrementally
}

// 🐌 Memory Inefficient: Buffers entire output in memory
const result = await $`cat huge-file.log`;
processFile(result.stdout); // Loads everything into memory

// ⚡ Fastest: Sync execution for small, quick commands
const quickResult = $`pwd`.sync();

// 🔄 Best for UX: Async with events for long-running commands
$`npm install`
  .on('stdout', showProgress)
  .start();

Testing

# Run comprehensive test suite (518+ tests)
bun test

# Run tests with coverage report
bun test --coverage

# Run specific test categories
npm run test:features    # Feature comparison tests
npm run test:builtin     # Built-in commands tests  
npm run test:pipe        # .pipe() method tests
npm run test:sync        # Synchronous execution tests
npm run test:signal      # CTRL+C signal handling tests

Requirements

• Bun: >= 1.0.0 (primary runtime)
• Node.js: >= 20.0.0 (compatibility support)

Roadmap

🔄 Coming Soon

• TypeScript Support: Full .d.ts definitions and type safety
• Enhanced Shell Options: set -u (nounset) and set -o pipefail support
• More Built-in Commands: Additional cross-platform utilities

💡 Planned Features

• Performance Optimizations: Further Bun runtime optimizations
• Advanced Error Handling: Enhanced error context and debugging
• Plugin System: Extensible architecture for custom integrations

Contributing

We welcome contributions! Since command-stream is public domain software, your contributions will also be released into the public domain.

🚀 Getting Started

git clone https://github.com/link-foundation/command-stream.git
cd command-stream
bun install
bun test  # Run the full test suite

📋 Development Guidelines

• All features must have comprehensive tests
• Built-in commands should match bash/sh behavior exactly
• Maintain cross-platform compatibility (Windows, macOS, Linux)
• Follow the existing code style and patterns

🧪 Running Tests

bun test                    # All 518+ tests
bun test tests/pipe.test.mjs # Specific test file
npm run test:builtin        # Built-in commands only

License - Our Biggest Advantage

The Unlicense (Public Domain)

Unlike other shell utilities that require attribution (MIT, Apache 2.0), command-stream is released into the public domain. This means:

• ✅ No attribution required - Use it without crediting anyone
• ✅ No license files to include - Simplify your distribution
• ✅ No restrictions - Modify, sell, embed, whatever you want
• ✅ No legal concerns - It's as free as code can be
• ✅ Corporate friendly - No license compliance overhead

This makes command-stream ideal for:

• Commercial products where license attribution is inconvenient
• Embedded systems where every byte counts
• Educational materials that can be freely shared
• Internal tools without legal review requirements

> "This is free and unencumbered software released into the public domain."