SHExecutor

SHExecutor is a convenience wrapper for executing shell commands from with-in a ruby process.

It supports:

• blocking indefinitely, on exit you can get status, stdout and stderr
• blocking with timeout, on exit you can get status, stdout, stderr, timeout exception (then output streams are not available)
• non-blocking, then you get handles to the output streams and the status of the forked process
• replacement, then you get a replaced process and none of the above
• redirecting of stderr and stdout, separately, to file, with the option to overwrite or append

It does not support:

• streaming input to stdin
• being nested in an outer Timeout (see 'complications' below)

For any executor:

• you can ask status, which will tell you "not executed", current status (e.g. run or sleep) and "no longer executing"
• you can ask result, which gives you nil unless the process is no longer executing, in which case you get status (e.g. pid, exit code, sigints.)

For a full description of status, please see Process::Status

This gem is sponsored by Hetzner (Pty) Ltd - http://hetzner.co.za

Initialization options:

Required / optional:

  {
    :application_path                     # Path of the command to run
    :params                               # Parameters to pass the command
  }

  @@default_options = {
    :timeout => -1,                     # Seconds after which to raise Timeout::Error if not completed
    :protect_against_injection => true, # look for spaces in and tainted application path
    :stdout_path => nil,                # file to append stdout to
    :stderr_path => nil,                # file to append stderr to
    :append_stdout_path => true,        # if true, will append, otherwise will overwrite
    :append_stderr_path => true,        # if true, will append, otherwise will overwrite
    :replace => false,                  # replace the running process with the command
    :wait_for_completion => false,      # block until the command completes
    :timeout_sig_kill_retry => 500      # if timeout occurs, send TERM, and send signal 9 if still present after X ms
  }

Installation

Add this line to your application's Gemfile:

gem 'shexecutor'

And then execute:

$ bundle

Or install it yourself as:

$ gem install shexecutor

Module helpers

Blocking

result, stdout, stderr = ::SHExecutor::execute_blocking("/bin/ls", "/tmp/")

Blocking with timeout

result, stdout, stderr = ::SHExecutor::execute_and_timeout_after("/bin/sleep", "10", 2)

Non-blocking

thr, stdout_io, stderr_io = ::SHExecutor::execute_non_blocking("/bin/sleep", "20")

Executor API

Blocking

iut = SHExecutor::Executor.new({:wait_for_completion => true, :application_path => "/bin/echo", :params => ["hello world"]})
result = iut.execute
iut.flush
puts "After execution status is: #{iut.status}"
# "no longer executing"
puts "out: #{iut.stdout} err: #{iut.stderr}"
puts "#{result.pid} success? #{result.success?} with code #{result.exitstatus}"
puts "For more see: #{iut.result.methods}"

Blocking with timeout

iut = SHExecutor::Executor.new({:timeout => 1, :wait_for_completion => true, :application_path => "/bin/sleep", :params => ["2"]})
result = iut.execute
# Timeout::Error gets raised. The spawned process is killed with TERM, and then with signal 9 if it does not close in timeout_sig_kill_retry ms

Non-blocking

iut = SHExecutor::Executor.new({:wait_for_completion => false, :application_path => "/bin/sleep", :params => ["1"]})
stdout, stderr, thr = iut.execute
puts "Status: #{iut.status}"
puts "PID: #{thr.pid}"
# "run" or "sleep"
sleep 2
puts "Status: #{iut.status}"
# "no longer executing"

Replacing

iut = SHExecutor::Executor.new({:replace => true, :application_path => "/bin/echo", :params => ["Your process has been assimilated"]})
iut.execute

stdout and stderr

iut.flush
puts iut.stdout
puts iut.stderr

redirecting stdout and stderr

iut = SHExecutor::Executor.new({:wait_for_completion => true, :application_path => "/bin/echo", :params => ["this is stdoutin a file"], :stdout_path => "/tmp/mystdout", :stderr_path => "/tmp/mystderr", :append_stdout_path => false, :append_stderr_path => true})
iut.execute
iut.flush
puts iut.stdout
puts iut.stderr

Complications

Remember to call iut.flush in order to access stdout and stderr in the Executor object.

Nested timeouts can result in complications. Because Executor drains stdout and stderr to avoid dead-locking, these StringIO streams will raise an IOError if they are interrupted. The backtrace of these IOErrors will not contain information of an outer Timeout or other exception that interrupted the Executor. The code below illustrates the complication:

def shexecutor_complication
  result, stdout, stderr = ::SHExecutor::execute_and_timeout_after("/bin/sleep", "30", 20)
end

Timeout::timeout(5) do
  shexecutor_complication
end

# shexecutor.rb:in 'copy_stream': stream closed (IOError)

Contributing

Please send feedback and comments to the author at:

Ernst van Graan ernstvangraan@gmail.com

Thanks to Sheldon Hearn for review and great ideas that unblocked complex challenges (https://rubygems.org/profiles/sheldonh).