All About Spawn

Spawn = Fork + Exec, but works also on platforms which don't support fork.

The usage of spawn is often said to be cryptic. Here I'll describe common cases.

• system('ls')

  pid = spawn(['ls', 'ls'])
  Process.wait(pid)
  

• system('ls .')

  pid = spawn('ls', '.')
  Process.wait(pid)
  

• system('ls . &')

  pid = spawn('ls', '.')
  

• system('ls . > a.txt')

  pid = spawn('ls', '.', :out => 'a.txt')
  Process.wait(pid)
  

• system('ls . >> a.txt')

  pid = spawn('ls', '.', :out => ['a.txt', 'a'])
  Process.wait(pid)
  

• system('ls . >& a.txt')

  pid = spawn('ls', '.', [:out, :err] => ['a.txt', 'w'])
  Process.wait(pid)
  

• IO.popen('cat a.txt') {|io| p io.read

  i, o = IO.pipe
  spawn('cat a.txt', :out => o)
  o.close
  p i.read
  

• system('make all &')

  spawn('make', 'all)
  

• Dir.chdir('a') { system 'make all &' }

  spawn('make', 'all', :chdir => 'a')
  

• Passing ENV:

  • Shell: $ AAA=1 make all &
  • Ruby: ENV['AAA'] = '1'; system('make all &')
  • Ruby with Spawn: spawn({'AAA' => '1'}, 'make', 'all')

Further information can be available in process.c in ruby trunk. Here the documentation from the file: