Module: ShellOut

Defined in:
lib/dolzenko/shell_out.rb

Overview

## ShellOut

Provides a convenient feature-rich way to “shell out” to external commands. Most useful features come from using ‘PTY` to execute the command. Not available on Windows, `Kernel#system` will be used instead.

## Features

### Interruption

The external command can be easily interrupted and ‘Interrupt` exception will propagate to the calling program.

For example while something like this can hang your terminal

loop { system("ls -R /") } # => lists directories indefinitely,
                           # Ctrl-C only stops ls

That won’t be the case with ShellOut:

require "shell_out"
include ShellOut
loop { shell_out("ls -R /") } # => when Ctrl-C is pressed ls is terminated
                              # and Interrupt exception is propagated

Yes it’s possible to examine the ‘$CHILD_STATUS.exitstatus` variable but that’s not nearly as robust and flexible as ‘PTY` solution.

### TTY-like Output

External command is running in pseudo TTY provided by ‘PTY` library on Unix, which means that commands like `ffmpeg`, `git` can report progress and **otherwise interact with user as usual**.

### Output Capturing

Output of the command can be captured using ‘:out` option

io = StringIO.new
shell_out("echo 42", :out => io) # doesn't print anything
io.string.chomp # => "42"

If ‘:out => :return` option is passed - the `shell_out` return the output of the command instead of exit status.

### :raise_exceptions, :verbose, :noop, and :dry_run Options

  • ‘:raise_exceptions => true` will raise `ShellOutException` for any non-zero

exit status of the command

Following options have the same semantics as ‘FileUtils` method options do

  • ‘:verbose => true` will echo command before execution

  • ‘:noop => true` will just return zero exit status without executing the command

  • ‘:dry_run => true` equivalent to `:verbose => true, :noop => true`

Defined Under Namespace

Classes: ShellOutException

Constant Summary collapse

CTRL_C_CODE = 
?\C-c
SUCCESS_EXIT_STATUS = 
0

Class Method Summary collapse

Class Method Details

.after(exitstatus, out_stream, *args) ⇒ Object 



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# File 'lib/dolzenko/shell_out.rb', line 83

def after(exitstatus, out_stream, *args)
  if args.last.is_a?(Hash) && args.last[:raise_exceptions] == true
    unless exitstatus == SUCCESS_EXIT_STATUS
      raise ShellOutException, "`#{ args[0..-2].join(" ") }' command finished with non-zero (#{ exitstatus }) exit status"
    end
  end
  if args.last.is_a?(Hash) && args.last[:out] == :return
    out_stream.rewind if out_stream.is_a?(StringIO)
    out_stream.read
  else
    exitstatus
  end
end

.before(*args) ⇒ Object 



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# File 'lib/dolzenko/shell_out.rb', line 68

def before(*args)
  if args.last.is_a?(Hash)
    options = args.last
    
    verbose, dry_run, noop = options.delete(:verbose), options.delete(:dry_run), options.delete(:noop)
    verbose = noop = true if dry_run

    puts "Executing: #{ args[0..-2].join(" ") }" if verbose

    return false if noop
  end

  true
end

.command(*args) ⇒ Object 



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# File 'lib/dolzenko/shell_out.rb', line 97

def command(*args)
  stripped_command = args.dup
  stripped_command.pop if stripped_command[-1].is_a?(Hash) # remove options
  stripped_command.shift if stripped_command[0].is_a?(Hash) # remove env
  stripped_command.join(" ")
end

.getopt(opt, default, *args) ⇒ Object 



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# File 'lib/dolzenko/shell_out.rb', line 120

def getopt(opt, default, *args)
  if args.last.is_a?(Hash)
    if opt == :out && args.last[:out] == :return
      StringIO.new
    else
      args.last.fetch(opt, default)
    end
  else
    default
  end
end

.shell_out ⇒ Object

.shell_out_with_pty(*args) ⇒ Object 



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# File 'lib/dolzenko/shell_out.rb', line 135

def shell_out_with_pty(*args)
  old_state = `stty -g`
  
  return SUCCESS_EXIT_STATUS unless ShellOut::before(*args)

  begin
    # stolen from ruby/ext/pty/script.rb
    # disable echoing and enable raw (not having to press enter)
    system "stty -echo raw lnext ^_"

    in_stream = ShellOut.getopt(:in, STDIN, *args)
    out_stream = ShellOut.getopt(:out, STDOUT, *args)
    writer = nil
    spawned_pid = nil
    ShellOut.with_env(*args) do
      PTY.spawn(ShellOut.command(*args)) do |r_pty, w_pty, pid|
        spawned_pid = pid
        reader = Thread.current
        writer = Thread.new do
          while true
            break if (ch = in_stream.getc).nil?
            ch = ch.chr
            if ch == ShellOut::CTRL_C_CODE
              reader.raise Interrupt, "Interrupted by user"
            else
              w_pty.print ch
              w_pty.flush
            end
          end
        end
        writer.abort_on_exception = true

        loop do
          c = begin
            r_pty.getc
          rescue Errno::EIO, EOFError
            nil
          end
          break if c.nil?

          out_stream.print c
          out_stream.flush
        end

        begin
          # try to invoke waitpid() before the signal handler does it
          return ShellOut::after(Process::waitpid2(pid)[1].exitstatus, out_stream, *args)
        rescue Errno::ECHILD
          # the signal handler managed to call waitpid() first;
          # PTY::ChildExited will be delivered pretty soon, so just wait for it
          sleep 1
        end
      end
    end
  rescue PTY::ChildExited => e
    return ShellOut::after(e.status.exitstatus, out_stream, *args)
  ensure
    if writer
      writer.kill rescue nil
    end

    if spawned_pid
      Process.kill(-9, spawned_pid) rescue nil
    end

    system "stty #{ old_state }"
  end
end

.shell_out_with_system(*args) ⇒ Object 



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# File 'lib/dolzenko/shell_out.rb', line 204

def shell_out_with_system(*args)
  return SUCCESS_EXIT_STATUS unless ShellOut::before(*args)

  cleaned_args = if args.last.is_a?(Hash)
    cleaned_options = args.last.dup.delete_if { |k, | [ :verbose, :raise_exceptions ].include?(k) }
    require "stringio"
    if cleaned_options[:out].is_a?(StringIO) ||
            cleaned_options[:out] == :return
      r, w = IO.pipe
      cleaned_options[:out] = w
      cleaned_options[:err] = [ :child, :out ]
    end
    if cleaned_options[:in].is_a?(StringIO)
      in_r, in_w = IO.pipe
      in_w.write cleaned_options[:in].read
      in_w.close
      cleaned_options[:in] = in_r
    end
    cleaned_options.empty? ? args[0..-2] : args[0..-2].dup << cleaned_options
  else
    args
  end

  exitstatus = if Kernel.system(*cleaned_args)
    SUCCESS_EXIT_STATUS
  else
    require "English"
    $CHILD_STATUS.exitstatus
  end

  if r
    w.close
    unless args.last[:out] == :return
      args.last[:out] << r.read
    end
  end

  ShellOut::after(exitstatus, r, *args)
end

.with_env(*args) ⇒ Object 



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# File 'lib/dolzenko/shell_out.rb', line 104

def with_env(*args)
  yield unless (env = args[0]).is_a?(Hash)
  stored_env = {}
  for name, value in env
    stored_env[name] = ENV[name]
    value == nil ? ENV.delete(name) : ENV[name] = value 
  end
  begin
    yield
  ensure
    for name, value in stored_env
      ENV[name] = value
    end
  end
end