Class: MCollective::Shell

Inherits:
Object
  • Object
show all
Defined in:
lib/mcollective/shell.rb

Overview

Wrapper around systemu that handles executing of system commands in a way that makes stdout, stderr and status available. Supports timeouts and sets a default sane environment.

s = Shell.new("date", opts)
s.runcommand
puts s.stdout
puts s.stderr
puts s.status.exitstatus

Options hash can have:

cwd         - the working directory the command will be run from
stdin       - a string that will be sent to stdin of the program
stdout      - a variable that will receive stdout, must support <<
stderr      - a variable that will receive stdin, must support <<
environment - the shell environment, defaults to include LC_ALL=C
              set to nil to clear the environment even of LC_ALL
timeout     - a timeout in seconds after which the subprocess is killed,
              the special value :on_thread_exit kills the subprocess
              when the invoking thread (typically the agent) has ended

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(command, options = {}) ⇒ Shell

Returns a new instance of Shell.



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# File 'lib/mcollective/shell.rb', line 27

def initialize(command, options={})
  @environment = {"LC_ALL" => "C"}
  @command = command
  @status = nil
  @stdout = ""
  @stderr = ""
  @stdin = nil
  @cwd = Dir.tmpdir
  @timeout = nil

  options.each do |opt, val|
    case opt.to_s
    when "stdout"
      raise "stdout should support <<" unless val.respond_to?("<<")

      @stdout = val

    when "stderr"
      raise "stderr should support <<" unless val.respond_to?("<<")

      @stderr = val

    when "stdin"
      raise "stdin should be a String" unless val.is_a?(String)

      @stdin = val

    when "cwd"
      raise "Directory #{val} does not exist" unless File.directory?(val)

      @cwd = val

    when "environment"
      if val.nil?
        @environment = {}
      else
        @environment.merge!(val.dup)
        @environment = @environment.delete_if { |_k, v| v.nil? }
      end

    when "timeout"
      raise "timeout should be a positive integer or the symbol :on_thread_exit symbol" unless val.eql?(:on_thread_exit) || (val.is_a?(Integer) && val > 0)

      @timeout = val
    end
  end
end

Instance Attribute Details

#command ⇒ Object (readonly)

Returns the value of attribute command.



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# File 'lib/mcollective/shell.rb', line 25

def command
  @command
end

#cwd ⇒ Object (readonly)

Returns the value of attribute cwd.



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# File 'lib/mcollective/shell.rb', line 25

def cwd
  @cwd
end

#environment ⇒ Object (readonly)

Returns the value of attribute environment.



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# File 'lib/mcollective/shell.rb', line 25

def environment
  @environment
end

#status ⇒ Object (readonly)

Returns the value of attribute status.



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# File 'lib/mcollective/shell.rb', line 25

def status
  @status
end

#stderr ⇒ Object (readonly)

Returns the value of attribute stderr.



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# File 'lib/mcollective/shell.rb', line 25

def stderr
  @stderr
end

#stdin ⇒ Object (readonly)

Returns the value of attribute stdin.



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# File 'lib/mcollective/shell.rb', line 25

def stdin
  @stdin
end

#stdout ⇒ Object (readonly)

Returns the value of attribute stdout.



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# File 'lib/mcollective/shell.rb', line 25

def stdout
  @stdout
end

#timeout ⇒ Object (readonly)

Returns the value of attribute timeout.



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# File 'lib/mcollective/shell.rb', line 25

def timeout
  @timeout
end

Instance Method Details

#runcommand ⇒ Object

Actually does the systemu call passing in the correct environment, stdout and stderr



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# File 'lib/mcollective/shell.rb', line 76

def runcommand
  opts = {"env" => @environment,
          "stdout" => @stdout,
          "stderr" => @stderr,
          "cwd" => @cwd}

  opts["stdin"] = @stdin if @stdin

  thread = Thread.current
  # Start a double fork and exec with systemu which implies a guard thread.
  # If a valid timeout is configured the guard thread will terminate the
  # executing process and reap the pid.
  # If no timeout is specified the process will run to completion with the
  # guard thread reaping the pid on completion.
  @status = systemu(@command, opts) do |cid|
    begin
      if timeout.is_a?(Integer)
        # wait for the specified timeout
        sleep timeout
      else
        # sleep while the agent thread is still alive
        sleep 0.1 while thread.alive?
      end

      # if the process is still running
      if Process.kill(0, cid)
        # and a timeout was specified
        if timeout
          if Util.windows?
            Process.kill("KILL", cid)
          else
            # Kill the process
            Process.kill("TERM", cid)
            sleep 2
            Process.kill("KILL", cid) if Process.kill(0, cid) # rubocop:disable Metrics/BlockNesting
          end
        end
        # only wait if the parent thread is dead
        Process.waitpid(cid) unless thread.alive?
      end
    rescue SystemExit # rubocop:disable Lint/SuppressedException
    rescue Errno::ESRCH # rubocop:disable Lint/SuppressedException
    rescue Errno::ECHILD
      Log.warn("Could not reap process '#{cid}'.")
    rescue Exception => e # rubocop:disable Lint/RescueException
      Log.info("Unexpected exception received while waiting for child process: #{e.class}: #{e}")
    end
  end
  @status.thread.kill
  @status
end