TTY-Exit: terminal exit codes for humans and machines

TTY::Exit

Terminal exit codes for humans and machines.

The goal of this library is to provide human friendly and standard way to use exit status codes in command line applications. Instead of saying exit(64) , you can say exit_with(:usage_error) . Both indicate a failure to the parent process but the :usage_error is so much nicer! Wouldn't you agree? That's why tty-exit gathers a list of all the most common exit codes as used by POSIX-compliant tools on different Unix systems for you to use.

The exit statuses range from 0 to 255 (inclusive). Any other exit status than 0 indicates a failure of some kind. The exit codes in the range 64-78 are adapted from the OpenBSD sysexits.h . The codes between 125 and 128 are reserved for shell statuses as defined in Advanced Bash Scripting Guide, Appendix E . The codes in the 129-154 range correspond with the fatal signals as defined in signal .

TTY::Exitprovides independent terminal exit codes component for TTY toolkit.

Installation

Add this line to your application's Gemfile:

gem 'tty-exit'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install tty-exit

Contents

1. Usage

To exit from any program use exit_with method. Instead of a number, you can use a readable name for the exit status:

TTY::Exit.exit_with(:usage_error)

The above will exit program immediately with an exit code indicating a failure:

puts $?.exitstatus
# => 64

All the reserved exit statuses have a matching exit message. To display a default message, as a second argument to exit_with you can pass :default value:

TTY::Exit.exit_with(:usage_error, :default)

That will produce the following user friendly message:

# => "ERROR(64): Command line usage error"

The preferred way is to include TTY::Exit module in your code:

class Command
  include TTY::Exit

  def execute
    exit_with(:config_error, :default)
  end
end

This will print an error message and return appropriate exit status:

cmd = Command.new
cmd.execute
# => "ERROR(78): Configuration Error"
puts $?.exitstatus
# => 78

To see the full list of reserved exit codes go tosection.

2. API

2.1 exit_code

There are many built-in exit codes that can be referenced using a name.

For example to return an exit code denoting success, you can use :ok or :success :

TTY::Exit.exit_code(:ok) # => 0
TTY::Exit.exit_code(:success) # => 0

Any other exit status than 0 indicates a failure of some kind. For example, when a command cannot be found use :not_found :

TTY::Exit.exit_code(:not_found)
# => 127

You can also use an exit code directly:

TTY::Exit.exit_code(127)
# => 127

2.2 exit_message

One of the downsides of exit codes is that they are not very communicative to the user. Why not have both? An exit code and a user friendly message. That's what exit_message is for. All the reserved exit codes have corresponding user friendly messages.

For example, when returning exit code 64 for usage error:

TTY::Exit.exit_message(:usage_error)
TTY::Exit.exit_message(64)

Will return:

# => "ERROR(64): Command line usage error"

The default messages are used by the exit_with method and can be overwritten by a custom one.

2.3 exit_with

To exit program with an exit code use exit_with . This method accepts a name or a code for the exit status.

TTY::Exit.exit_with(:usage_error)
TTY::Exit.exit_with(64)

Both will produce the same outcome.

As a second argument you can specify a user friendly message to be printed to stderr before exit. To use predefined messages use :default as a value:

TTY::Exit.exit_with(:usage_error, :default)
# => "ERROR(64): Command line usage error"

Optionally, you can provide a custom message to display to the user.

TTY::Exit.exit_with(:usge_error, "Wrong arguments")
# => "Wrong arguments"

Finally, you can redirect output to a different stream using :io option. By default, message is printed to stderr :

TTY::Exit.exit_with(:usage_error, io: $stdout)

Since TTY::Exit is a module, you can include it in your code to get access to all the methods:

class Command
  include TTY::Exit

  def execute
    exit_with(:usage_error, :default)
  end
end

2.4 register_exit

If the provided exit codes don't match your needs, you can add your own using the register_exit method.

For example, to register a custom exit with :too_long name and the status 7 that will notify user and programs about too many arguments do:

class Command
  include TTY::Exit

  register_exit(:too_long, 7, "Argument list too long")

  def execute
    exit_with(:too_long, :default)
  end
end

Then when the command gets run:

cmd = Command.new
cmd.execute
# =>
# ERROR(7): Argument list too long

2.5 exit_reserved?

To check if an exit code is already reserved by Unix system use exit_reserved? . This is useful in situations where you want to add it your command line application custom exit codes. The check accepts only integer numbers in range 0 to 255 inclusive:

TTY::Exit.exit_reserved?(126) # => true
TTY::Exit.exit_reserved?(100) # => false

2.6 exit_valid?

The exit statuses range from 0 to 255 (inclusive). The exit_valid? method helps you check if an exit status is within the range or not.

TTY::Exit.exit_valid?(11) # => true
TTY::Exit.exit_valid?(522) # => false

2.7 exit_success?

Any other exit status than 0 indicates a failure of some kind. The exit_success? is a more descriptive way to determine if a program succeeded or not.

TTY::Exit.exit_success?(0) # => true
TTY::Exit.exit_success?(7) # => false

2.8 exit_codes

You can access all the predefined exit codes and their names with exit_codes method:

TTY::Exit.exit_codes
# =>
# "{:ok=>0, :success=>0, :error=>1, :shell_misuse=>2, :usage_error=>64, :data_error=>65, ... }"

2.9 exit_messages

To see what default messages are for the predefined exit codes use exit_messages :

TTY::Exit.exit_messages
# =>
# "{0=>"Successful termination", 1=>"An error occurred", 2=>"Misuse of shell builtins", 64=>"Command line usage error", ... }"

The exit statuses range from 0 to 255 (inclusive). Any other exit status than 0 indicates a failure of some kind. The exit codes in the range 64-78 are adapted from the OpenBSD sysexits.h . The codes between 125 and 128 are reserved for shell statuses as defined in Advanced Bash Scripting Guide, Appendix E . The codes in the 129-154 range correspond with the fatal signals as defined in signal .

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.

To install this gem onto your local machine, run bundle exec rake install . To release a new version, update the version number in version.rb , and then run bundle exec rake release , which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org .

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/piotrmurach/tty-exit . This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct .

License

The gem is available as open source under the terms of the MIT License .

Code of Conduct

Everyone interacting in the TTY::Exit project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct .

Copyright

Copyright (c) 2020 Piotr Murach. See LICENSE for further details.