ptlis/shell-command

A basic wrapper around execution of shell commands.

1.0.0 2019-08-10 15:58 UTC

README

A developer-friendly wrapper around execution of shell commands.

There were several goals that inspired the creation of this package:

  • Use the command pattern to encapsulate the data required to execute a shell command, allowing the command to be passed around and executed later.
  • Maintain a stateless object graph allowing (for example) the spawning of multiple running processes from a single command.
  • Provide clean APIs for synchronous and asynchronous usage.
  • Running processes can be wrapped in promises to allow for easy composition.

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Install

From the terminal:

    $ composer require ptlis/shell-command

Usage

The Builder

The package ships with a command builder, providing a simple and safe method to build commands.

    use ptlis\ShellCommand\CommandBuilder;
    
    $builder = new CommandBuilder();

The builder will attempt to determine your environment when constructed, you can override this by specifying an environment as the first argument:


    use ptlis\ShellCommand\CommandBuilder;
    use ptlis\ShellCommand\UnixEnvironment;
    
    $builder = new CommandBuilder(new UnixEnvironment());

Note: this builder is immutable - method calls must be chained and terminated with a call to buildCommand like so:

    $command = $builder
        ->setCommand('foo')
        ->addArgument('--bar=baz')
        ->buildCommand()

Set Command

First we must provide the command to execute:

    $builder->setCommand('git')             // Executable in $PATH
        
    $builder->setCommand('./local/bin/git') // Relative to current working directory
        
    $builder->setCommand('/usr/bin/git')    // Fully qualified path
    
    $build->setCommand('~/.script.sh')      // Path relative to $HOME

If the command is not locatable a RuntimeException is thrown.

Set Process Timeout

The timeout (in microseconds) sets how long the library will wait on a process before termination. Defaults to -1 which never forces termination.

    $builder
        ->setTimeout(30 * 1000 * 1000)          // Wait 30 seconds

If the process execution time exceeds this value a SIGTERM will be sent; if the process then doesn't terminate after a further 1 second wait then a SIGKILL is sent.

Set Poll Timeout

Set how long to wait (in microseconds) between polling the status of processes. Defaults to 1,000,000 (1 second).

    $builder
        ->setPollTimeout(30 * 1000 * 1000)          // Wait 30 seconds

Set Working Directory

You can set the working directory for a command:

    $builder
        ->setCwd('/path/to/working/directory/')

Add Arguments

Add arguments to invoke the command with (all arguments are escaped):

    $builder
        ->addArgument('--foo=bar')

Conditionally add, depending on the result of an expression:

    $builder
        ->addArgument('--foo=bar', $myVar === 5)

Add several arguments:

    $builder
        ->addArguments([
            '--foo=bar',
            '-xzcf',
            'if=/dev/sda of=/dev/sdb'
        ])

Conditionally add, depending on the result of an expression:

    $builder
        ->addArguments([
            '--foo=bar',
            '-xzcf',
            'if=/dev/sda of=/dev/sdb'
        ], $myVar === 5)

Note: Escaped and raw arguments are added to the command in the order they're added to the builder. This accommodates commands that are sensitive to the order of arguments.

Add Raw Arguments

WARNING: Do not pass user-provided data to these methods! Malicious users could easily execute arbitrary shell commands.

Arguments can also be applied without escaping:

    $builder
        ->addRawArgument("--foo='bar'")

Conditionally, depending on the result of an expression:

    $builder
        ->addRawArgument('--foo=bar', $myVar === 5)

Add several raw arguments:

    $builder
        ->addRawArguments([
            "--foo='bar'",
            '-xzcf',
        ])

Conditionally, depending on the result of an expression:

    $builder
        ->addRawArguments([
            '--foo=bar',
            '-xzcf',
            'if=/dev/sda of=/dev/sdb'
        ], $myVar === 5)

Note: Escaped and raw arguments are added to the command in the order they're added to the builder. This accommodates commands that are sensitive to the order of arguments.

Add Environment Variables

Environment variables can be set when running a command:

    $builder
        ->addEnvironmentVariable('TEST_VARIABLE', '123')

Conditionally, depending on the result of an expression:

    $builder
        ->addEnvironmentVariable('TEST_VARIABLE', '123', $myVar === 5)

Add several environment variables:

    $builder
        ->addEnvironmentVariables([
            'TEST_VARIABLE' => '123',
            'FOO' => 'bar'
        ])

Conditionally, depending on the result of an expression:

    $builder
        ->addEnvironmentVariables([
            'TEST_VARIABLE' => '123',
            'FOO' => 'bar'
        ], $foo === 5)

Add Process Observers

Observers can be attached to spawned processes. In this case we add a simple logger:

    $builder
        ->addProcessObserver(
            new AllLogger(
                new DiskLogger(),
                LogLevel::DEBUG
            )
        )

Build the Command

One the builder has been configured, the command can be retrieved for execution:

    $command = $builder
        // ...
        ->buildCommand();

Synchronous Execution

To run a command synchronously use the runSynchronous method. This returns an object implementing CommandResultInterface, encoding the result of the command.

    $result = $command
        ->runSynchronous(); 

When you need to re-run the same command multiple times you can simply invoke runSynchronous repeatedly; each call will run the command returning the result to your application.

The exit code & output of the command are available as methods on this object:

    $result->getExitCode();     // 0 for success, anything else conventionally indicates an error
    $result->getStdOut();       // The contents of stdout (as a string)
    $result->getStdOutLines();  // The contents of stdout (as an array of lines)
    $result->getStdErr();       // The contents of stderr (as a string)
    $result->getStdErrLines();  // The contents of stderr (as an array of lines)

Asynchronous execution

Commands can also be executed asynchronously, allowing your program to continue executing while waiting for the result.

Command::runAsynchronous

The runAsynchronous method returns an object implementing the ProcessInterface which provides methods to monitor the state of a process.

    $process = $command->runAsynchronous();

As with the synchronouse API, when you need to re-run the same command multiple times you can simply invoke runAsynchronous repeatedly; each call will run the command returning the object representing the process to your application.

ProcessInterface provides the methods required to monitor the state and lifecycle of a process.

Check whether the process has completed:

    if (!$process->isRunning()) {
        echo 'done' . PHP_EOL;
    }

Force the process to stop:

    $process->stop();

Wait for the process to stop (this blocks execution of your script, effectively making this synchronous):

    $process->wait();

Get the process id (throws a \RuntimeException if the process has ended):

    $process->getPid();

Read output from a stream:

    $stdOut = $process->readStream(ProcessInterface::STDOUT);

Get the exit code (throws a \RuntimeException if the process is still running):

    $exitCode = $process->getExitCode();

Send a signal (SIGTERM or SIGKILL) to the process:

    $process->sendSignal(ProcessInterface::SIGTERM);

Get the string representation of the running command:

    $commandString = $process->getCommand();

Process::getPromise

Monitoring of shell command execution can be wrapped in a ReactPHP Promise. This gives us a flexible execution model, allowing chaining (with Promise::then) and aggregation using Promise::all, Promise::some, Promise::race and their friends.

Building promise to execute a command can be done by calling the getPromise method from a Process instance. This returns an instance of \React\Promise\Promise:

    $eventLoop = \React\EventLoop\Factory::create();

    $promise = $command->runAsynchonous()->getPromise($eventLoop);

The ReactPHP EventLoop component is used to periodically poll the running process to see if it has terminated yet; once it has the promise is either resolved or rejected depending on the exit code of the executed command.

The effect of this implementation is that once you've created your promises, chains and aggregates you must invoke EventLoop::run:

    $eventLoop->run();

This will block further execution until the promises are resolved/rejected.

Mocking

Mock implementations of the Command & Builder interfaces are provided to aid testing.

By type hinting against the interfaces, rather than the concrete implementations, these mocks can be injected & used to return pre-configured result objects.

Contributing

You can contribute by submitting an Issue to the issue tracker, improving the documentation or submitting a pull request. For pull requests i'd prefer that the code style and test coverage is maintained, but I am happy to work through any minor issues that may arise so that the request can be merged.

Known limitations

  • Currently supports UNIX environments only.