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> Run external commands with pretty output logging and capture stdout, stderr and exit status. Redirect stdin, stdout and stderr of each command to a file or a string.

**TTY::Command** provides independent command execution component for [TTY](https://github.com/piotrmurach/tty) toolkit.

## Motivation

Complex software projects aren't just a single app. These projects usually spawn dozens or hundreds of supplementary standalone scripts which are just as important as the app itself. Examples include - data validation, deployment, monitoring, database maintenance, backup & restore, configuration management, crawling, ETL, analytics, log file processing, custom reports, etc. One of the contributors to **TTY::Command** counted 222 scripts in the `bin` directory for his startup.

Why should we be handcuffed to `sh` or `bash` for these scripts when we could be using Ruby? Ruby is easier to write and more fun, and we gain a lot by using a better language. It's nice for everyone to just use Ruby everywhere.

**TTY::Command** tries to add value in other ways. It'll halt automatically if a command fails. It's easy to get verbose or quiet output as appropriate, or even capture output and parse it with Ruby. Escaping arguments is a breeze. These are all areas where traditional shell scripts tend to fall flat.

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'tty-command'
```

And then execute:

    $ bundle

Or install it yourself as:

    $ gem install tty-command

## Contents

* [1. Usage](#1-usage)
* [2. Interface](#2-interface)
  * [2.1. Run](#21-run)
  * [2.2. Run!](#22-run)
  * [2.3. Logging](#23-logging)
    * [2.3.1. Color](#231-color)
    * [2.3.2. UUID](#232-uuid)
    * [2.3.3. Only output on error](#233-only-output-on-error)
    * [2.3.4. Verbose](#234-verbose)
  * [2.4. Dry run](#24-dry-run)
  * [2.5. Wait](#25-wait)
  * [2.6. Test](#26-test)
  * [2.7. Ruby interpreter](#27-ruby-interpreter)
* [3. Advanced Interface](#3-advanced-interface)
  * [3.1. Environment variables](#31-environment-variables)
  * [3.2. Options](#32-options)
    * [3.2.1. Redirection](#321-redirection)
    * [3.2.2. Handling input](#322-handling-input)
    * [3.2.3. Timeout](#323-timeout)
    * [3.2.4. Binary mode](#324-binary-mode)
    * [3.2.5. Signal](#325-signal)
    * [3.2.6. PTY(pseudo-terminal)](#326-ptypseudo-terminal)
    * [3.2.7. Current directory](#327-current-directory)
    * [3.2.8. User](#328-user)
    * [3.2.9. Group](#329-group)
    * [3.2.10. Umask](#3210-umask)
  * [3.3. Result](#33-result)
    * [3.3.1. success?](#331-success)
    * [3.3.2. failure?](#332-failure)
    * [3.3.3. exited?](#333-exited)
    * [3.3.4. each](#334-each)
  * [3.4. Custom printer](#34-custom-printer)
* [4. Example](#4-example)

## 1. Usage

Create a command instance and then run some commands:

```ruby
require 'tty-command'

cmd = TTY::Command.new
cmd.run('ls -la')
cmd.run('echo Hello!')
```

Note that `run` will throw an exception if the command fails. This is already an improvement over ordinary shell scripts, which just keep on going when things go bad. That usually makes things worse.

You can use the return value to capture stdout and stderr:

```ruby
out, err = cmd.run('cat ~/.bashrc | grep alias')
```

Instead of using a plain old string, you can break up the arguments and they'll get escaped if necessary:

```ruby
path = "hello world"
FileUtils.touch(path)
cmd.run("sum #{path}")  # this will fail due to bad escaping
cmd.run("sum", path)    # this gets escaped automatically
```

## 2. Interface

### 2.1 Run

Run starts the specified command and waits for it to complete.

The argument signature of `run` is as follows:

`run([env], command, [argv1, ...], [options])`

The `env`, `command` and `options` arguments are described in the following sections.

For example, to display file contents:

```ruby
cmd.run('cat file.txt')
```

If the command succeeds, a `TTY::Command::Result` is returned that records stdout and stderr:

```ruby
out, err = cmd.run('date')
puts "The date is #{out}"
# => "The date is Tue 10 May 2016 22:30:15 BST\n"
```

You can also pass a block that gets invoked anytime stdout and/or stderr receive output:

```ruby
cmd.run('long running script') do |out, err|
  output << out if out
  errors << err if err
end
```

If the command fails (with a non-zero exit code), a `TTY::Command::ExitError` is raised. The `ExitError` message will include:

  * the name of command executed
  * the exit status
  * stdout bytes
  * stderr bytes

If the error output is very long, the stderr may contain only a prefix, number of omitted bytes and suffix.

### 2.2 Run!

If you expect a command to fail occasionally, use `run!` instead. Then you can detect failures and respond appropriately. For example:

```ruby
if cmd.run!('which xyzzy').failure?
  cmd.run('brew install xyzzy')
end
```

### 2.3 Logging

By default, when a command is run, the command and the output are printed to `stdout` using the `:pretty` printer. If you wish to change printer you can do so by passing a `:printer` option:

* `:null` - no output
* `:pretty` - colorful output
* `:progress` - minimal output with green dot for success and F for failure
* `:quiet` - only output actual command stdout and stderr

like so:

```ruby
cmd = TTY::Command.new(printer: :progress)
```

By default the printers log to `stdout` but this can be changed by passing an object that responds to `<<` message:

```ruby
logger = Logger.new('dev.log')
cmd = TTY::Command.new(output: logger)
```

You can force the printer to always in print in color by passing the `:color` option:

```ruby
cmd = TTY::Command.new(color: true)
```

#### 2.3.1 Color

When using printers you can switch off coloring by using `:color` option set to `false`.

#### 2.3.2 UUID

By default, when logging is enabled and `pretty` printer is used, each log entry is prefixed by specific command run uuid number. This number can be switched off using the `:uuid` option at initialization:

```ruby
cmd = TTY::Command.new(uuid: false)
cmd.run('rm -R all_my_files')
# =>
#  Running rm -r all_my_files
#  ...
#  Finished in 6 seconds with exit status 0 (successful)
```

or individually per command run:

```rub
cmd = TTY::Command.new
cmd.run("echo hello", uuid: false)
# =>
#  Running echo hello
#      hello
#  Finished in 0.003 seconds with exit status 0 (successful)
```

#### 2.3.3 Only output on error

When using a command that can fail, setting `:only_output_on_error` option to `true` hides the output if the command succeeds:

```ruby
cmd = TTY::Command.new
cmd.run('non_failing_command', only_output_on_error: true)
```

This will only print the `Running` and `Finished` lines, while:

```ruby
cmd.run('non_failing_command')
```

will also print any output that the `non_failing_command` might generate.

Running either:

```ruby
cmd.run('failing_command', only_output_on_error: true)
```

either:

```ruby
cmd.run('failing_command')
```

will also print the output.

*Setting this option will cause the output to show at once, at the end of the command.*

#### 2.3.4 Verbose

By default commands will produce warnings when, for example `pty` option is not supported on a given platform. You can switch off such warnings with `:verbose` option set to `false`.

```ruby
cmd.run("echo '\e[32mColors!\e[0m'", pty: true, verbose: false)
```

### 2.4 Dry run

Sometimes it can be useful to put your script into a "dry run" mode that prints commands without actually running them. To simulate execution of the command use the `:dry_run` option:

```ruby
cmd = TTY::Command.new(dry_run: true)
cmd.run(:rm, 'all_my_files')
# => [123abc] (dry run) rm all_my_files
```

To check what mode the command is in use the `dry_run?` query helper:

```ruby
cmd.dry_run? # => true
```

### 2.5 Wait

If you need to wait for a long running script and stop it when a given pattern has been matched use `wait` like so:

```ruby
cmd.wait 'tail -f /var/log/production.log', /something happened/
```

### 2.6 Test

To simulate classic bash test command you case use `test` method with expression to check as a first argument:

```ruby
if cmd.test '-e /etc/passwd'
  puts "Sweet..."
else
  puts "Ohh no! Where is it?"
  exit 1
end
```

### 2.7 Ruby interpreter

In order to run a command with Ruby interpreter do:

```ruby
cmd.ruby %q{-e "puts 'Hello world'"}
```

## 3. Advanced Interface

### 3.1 Environment variables

The environment variables need to be provided as hash entries, that can be set directly as a first argument:

```ruby
cmd.run({'RAILS_ENV' => 'PRODUCTION'}, :rails, 'server')
```

or as an option with `:env` key:

```ruby
cmd.run(:rails, 'server', env: {rails_env: :production})
```

When a value in env is nil, the variable is unset in the child process:

```ruby
cmd.run(:echo, 'hello', env: {foo: 'bar', baz: nil})
```

### 3.2 Options

When a hash is given in the last argument (options), it allows to specify a current directory, umask, user, group and and zero or more fd redirects for the child process.

#### 3.2.1 Redirection

There are few ways you can redirect commands output.

You can directly use shell redirection like so:

```ruby
out, err = cmd.run("ls 1&>2")
puts err
# =>
# CHANGELOG.md
# CODE_OF_CONDUCT.md
# Gemfile
# ...
```

You can provide redirection as additional hash options where the key is one of `:in`, `:out`, `:err`, an integer (a file descriptor for the child process), an IO or array. For example, `stderr` can be merged into stdout as follows:

```ruby
cmd.run(:ls, :err => :out)
cmd.run(:ls, :stderr => :stdout)
cmd.run(:ls, 2 => 1)
cmd.run(:ls, STDERR => :out)
cmd.run(:ls, STDERR => STDOUT)
```

The hash key and value specify a file descriptor in the child process (stderr & stdout in the examples).

You can also redirect to a file:

```ruby
cmd.run(:cat, :in => 'file')
cmd.run(:cat, :in => open('/etc/passwd'))
cmd.run(:ls, :out => 'log')
cmd.run(:ls, :out => "/dev/null")
cmd.run(:ls, :out => 'out.log', :err => "err.log")
cmd.run(:ls, [:out, :err] => "log")
cmd.run("ls 1>&2", :err => 'log')
```

It is possible to specify flags and permissions of file creation explicitly by passing an array value:

```ruby
cmd.run(:ls, :out => ['log', 'w']) # 0664 assumed
cmd.run(:ls, :out => ['log', 'w', 0600])
cmd.run(:ls, :out => ['log', File::WRONLY|File::EXCL|File::CREAT, 0600])
```

You can, for example, read data from one source and output to another:

```ruby
cmd.run("cat", :in => "Gemfile", :out => 'gemfile.log')
```

#### 3.2.2 Handling Input

You can provide input to stdin stream using the `:input` key. For instance, given the following executable called `cli` that expects name from `stdin`:

```ruby
name = $stdin.gets
puts "Your name: #{name}"
```

In order to execute `cli` with name input do:

```ruby
cmd.run('cli', input: "Piotr\n")
# => Your name: Piotr
```

Alternatively, you can pass input via the :in option, by passing a `StringIO` Object. This object might have more than one line, if the executed command reads more than once from STDIN.

Assume you have run a program, that first asks for your email address and then for a password:

```ruby
in_stream = StringIO.new
in_stream.puts "username@example.com"
in_stream.puts "password"
in_stream.rewind

cmd.run("my_cli_program", "login", in: in_stream).out
```

#### 3.2.3 Timeout

You can timeout command execuation by providing the `:timeout` option in seconds:

```ruby
cmd.run("while test 1; sleep 1; done", timeout: 5)
```

And to set it for all commands do:

```ruby
cmd = TTY::Command.new(timeout: 5)
```

Please run `examples/timeout.rb` to see timeout in action.

#### 3.2.4 Binary mode

By default the standard input, output and error are non-binary. However, you can change to read and write in binary mode by using the `:binmode` option like so:

```ruby
cmd.run("echo 'hello'", binmode: true)
```

To set all commands to be run in binary mode do:

```ruby
cmd = TTY::Command.new(binmode: true)
```

#### 3.2.5 Signal

You can specify process termination signal other than the defaut `SIGTERM`:

```ruby
cmd.run("whilte test1; sleep1; done", timeout: 5, signal: :KILL)
```

#### 3.2.6 PTY(pseudo terminal)

The `:pty` configuration option causes the command to be executed in subprocess where each stream is a `pseudo terminal`. By default this options is set to `false`.

If you require to interface with interactive subprocess then setting this option to `true` will enable a `pty` terminal device. For example, a command may emit colored output only if it is running via terminal device. You may also wish to run a program that waits for user input, and simulates typing in commands and reading responses.

This option will only work on systems that support BSD pty devices such as Linux or OS X, and it will gracefully fallback to non-pty device on all the other.

In order to run command in `pseudo terminal`, either set the flag globally for all commands:

```ruby
cmd = TTY::Command.new(pty: true)
```

or individually for each executed command:

```ruby
cmd.run("echo 'hello'", pty: true)
```

Please note that setting `:pty` to `true` may change how the command behaves. It's important to understand the difference between `interactive` and `non-interactive` modes. For example, executing `git log` to view the commit history in default `non-interactive` mode:

```ruby
cmd.run("git log") # => finishes and produces full output
```

However, in `interactive` mode with `pty` flag on:

```ruby
cmd.run("git log", pty: true) # => uses pager and waits for user input (never returns)
```

In addition, when pty device is used, any input to command may be echoed to the standard output, as well as some redirets may not work.

#### 3.2.7 Current directory

To change directory in which the command is run pass the `:chdir` option:

```ruby
cmd.run(:echo, 'hello', chdir: '/var/tmp')
```

#### 3.2.8 User

To run command as a given user do:

```ruby
cmd.run(:echo, 'hello', user: 'piotr')
```

#### 3.2.9 Group

To run command as part of group do:

```ruby
cmd.run(:echo, 'hello', group: 'devs')
```

#### 3.2.10 Umask

To run command with umask do:

```ruby
cmd.run(:echo, 'hello', umask: '007')
```

### 3.3 Result

Each time you run command the stdout and stderr are captured and return as result. The result can be examined directly by casting it to tuple:

```ruby
out, err = cmd.run(:echo, 'Hello')
```

However, if you want to you can defer reading:

```ruby
result = cmd.run(:echo, 'Hello')
result.out
result.err
```

#### 3.3.1 success?

To check if command exited successfully use `success?`:

```ruby
result = cmd.run(:echo, 'Hello')
result.success? # => true
```

#### 3.3.2 failure?

To check if command exited unsuccessfully use `failure?` or `failed?`:

```ruby
result = cmd.run(:echo, 'Hello')
result.failure?  # => false
result.failed?   # => false
```

#### 3.3.3 exited?

To check if command ran to completion use `exited?` or `complete?`:

```ruby
result = cmd.run(:echo, 'Hello')
result.exited?    # => true
result.complete?  # => true
```

#### 3.3.4 each

The result itself is an enumerable and allows you to iterate over the stdout output:

```ruby
result = cmd.run(:ls, '-1')
result.each { |line| puts line }
# =>
#  CHANGELOG.md
#  CODE_OF_CONDUCT.md
#  Gemfile
#  Gemfile.lock
#  ...
#  lib
#  pkg
#  spec
#  tasks
```

By default the linefeed character `\n` is used as a delimiter but this can be changed either globally by calling `record_separator`:

```ruby
TTY::Command.record_separator = "\n\r"
```

or configured per `each` call by passing delimiter as an argument:

```ruby
cmd.run(:ls, '-1').each("\t") { ... }
```

### 3.4 Custom printer

If the built-in printers do not meet your requirements you can create your own. At the very minimum you need to specify the `write` method that will be called during the lifecycle of command execution. The `write` accepts two arguments, first the currently run command instance and second the message to be printed:

```ruby
CustomPrinter < TTY::Command::Printers::Abstract
  def write(cmd, message)
    puts message
  end
end

printer = CustomPrinter

cmd = TTY::Command.new(printer: printer)
```

Please see [lib/tty/command/printers/abstract.rb](https://github.com/piotrmurach/tty-command/blob/master/lib/tty/command/printers/abstract.rb) for a full set of methods that you can override.

## 4. Example

Here's a slightly more elaborate example to illustrate how tty-command can improve on plain old shell scripts. This example installs a new version of Ruby on an Ubuntu machine.

```ruby
cmd = TTY::Command.new

# dependencies
cmd.run "apt-get -y install build-essential checkinstall"

# fetch ruby if necessary
if !File.exists?("ruby-2.3.0.tar.gz")
  puts "Downloading..."
  cmd.run "wget http://ftp.ruby-lang.org/pub/ruby/2.3/ruby-2.3.0.tar.gz"
  cmd.run "tar xvzf ruby-2.3.0.tar.gz"
end

# now install
Dir.chdir("ruby-2.3.0") do
  puts "Building..."
  cmd.run "./configure --prefix=/usr/local"
  cmd.run "make"
end
```

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/piotrmurach/tty-command. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](http://contributor-covenant.org) code of conduct.

## License

The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).

## Copyright

Copyright (c) 2016-2018 Piotr Murach. See LICENSE for further details.