Fork on Windows

Ruby
1

What’s the best way to see if a particular platform supports fork? I
know I could check if it’s running on Windows, but I’d like something
more direct (and presumably accurate).

A similar question: assuming a standard Ruby install (that is, no
popen4), what’s the most robust way of running a shell command and
capturing STDOUT and STDERR?
command 2>&1 seems to not always work on Windows.

2

On 1/1/07, Robert J. [email protected] wrote:

What’s the best way to see if a particular platform supports fork? I
know I could check if it’s running on Windows, but I’d like something
more direct (and presumably accurate).

You could test fork and see if you get a defined value back.

A similar question: assuming a standard Ruby install (that is, no
popen4), what’s the most robust way of running a shell command and
capturing STDOUT and STDERR?
command 2>&1 seems to not always work on Windows.

And it won’t. That’s bourne-shell syntax.

http://www.ruby-doc.org/stdlib/libdoc/open3/rdoc/index.html

Mike

3

Michael P. Soulier wrote:

You could test fork and see if you get a defined value back.

Not sure how to do this… Kernel.respond_to? :fork is true on both
platforms.

4

Not sure how to do this… Kernel.respond_to? :fork is true on both
platforms.

can you execute fork in windows and catch the exception if it fails ?

5

Uma G. wrote:

can you execute fork in windows and catch the exception if it fails ?

Nope - fork is used deep inside a lib. I’d like to exit right away if
the platform doesn’t support it, otherwise let the lib run as normal.

6

Nope - fork is used deep inside a lib. I’d like to exit right away if
the platform doesn’t support it, otherwise let the lib run as normal.

then do this exception test during the installation process

7

Uma G. wrote:

Not sure how to do this… Kernel.respond_to? :fork is true on both
platforms.

can you execute fork in windows and catch the exception if it fails ?

Is this like “stick a fork in it and see if it’s done?”

–
M. Edward (Ed) Borasky, FBG, AB, PTA, PGS, MS, MNLP, NST, ACMC(P)
http://borasky-research.blogspot.com/

If God had meant for carrots to be eaten cooked, He would have given
rabbits fire.

8

On Tue, 2 Jan 2007, Robert J. wrote:

What’s the best way to see if a particular platform supports fork? I
know I could check if it’s running on Windows, but I’d like something
more direct (and presumably accurate).

has_fork =
begin
fork{ exit }
Process.wait
true
rescue
false
end

A similar question: assuming a standard Ruby install (that is, no
popen4), what’s the most robust way of running a shell command and
capturing STDOUT and STDERR?
command 2>&1 seems to not always work on Windows.

NAME

systemu.rb

SYNOPSIS

univeral capture of stdout and stderr and handling of child process
pid for windows, *nix, etc.

URIS

http://rubyforge.org/projects/codeforpeople/
http://codeforpeople.com/lib/ruby/

INSTALL

gem install systemu

SAMPLES

<========< samples/a.rb >========>

~ > cat samples/a.rb

 #
 # systemu can be used on any platform to return status, stdout, and

stderr of
# any command. unlike other methods like open3/popen4 there is
zero danger of
# full pipes or threading issues hanging your process or
subprocess.
#
require ‘systemu’

   date = %q( ruby -e"  t = Time.now; STDOUT.puts t; STDERR.puts t

" )

   status, stdout, stderr = systemu date
   p [ status, stdout, stderr ]

~ > ruby samples/a.rb

 [#<Process::Status: pid=9960,exited(0)>, "Fri Nov 03 17:22:23 MST

2006\n", “Fri Nov 03 17:22:23 MST 2006\n”]

<========< samples/b.rb >========>

~ > cat samples/b.rb

 #
 # quite a few keys can be passed to the command to alter it's

behaviour. if
# either stdout or stderr is supplied those objects should
respond_to? ‘<<’
# and only status will be returned
#
require ‘systemu’

   date = %q( ruby -e"  t = Time.now; STDOUT.puts t; STDERR.puts t

" )

   stdout, stderr = '', ''
   status = systemu date, 'stdout' => stdout, 'stderr' => stderr
   p [ status, stdout, stderr ]

~ > ruby samples/b.rb

 [#<Process::Status: pid=9965,exited(0)>, "Fri Nov 03 17:22:23 MST

2006\n", “Fri Nov 03 17:22:23 MST 2006\n”]

<========< samples/c.rb >========>

~ > cat samples/c.rb

 #
 # of course stdin can be supplied too.  synonyms for 'stdin'

include ‘0’ and
# 0. the other stdio streams have similar shortcuts
#
require ‘systemu’

   cat = %q( ruby -e"  ARGF.each{|line| puts line}  " )

   status = systemu cat, 0=>'the stdin for cat', 1=>stdout=''
   puts stdout

~ > ruby samples/c.rb

 the stdin for cat

<========< samples/d.rb >========>

~ > cat samples/d.rb

 #
 # the cwd can be supplied
 #
   require 'systemu'
   require 'tmpdir'

   pwd = %q( ruby -e"  STDERR.puts Dir.pwd  " )

   status = systemu pwd, 2=>(stderr=''), :cwd=>Dir.tmpdir
   puts stderr

~ > ruby samples/d.rb

 /tmp

<========< samples/e.rb >========>

~ > cat samples/e.rb

 #
 # any environment vars specified are merged into the child's

environment
#
require ‘systemu’

   env = %q( ruby -r yaml -e"  puts ENV[ 'answer' ] " )

   status = systemu env, 1=>stdout='', 'env'=>{ 'answer' => 0b101010

}
puts stdout

~ > ruby samples/e.rb

 42

<========< samples/f.rb >========>

~ > cat samples/f.rb

 #
 # if a block is specified then it is passed the child pid and run

in a
# background thread. note that this thread will not be blocked
during the
# execution of the command so it may do useful work such as killing
the child
# if execution time passes a certain threshold
#
require ‘systemu’

   looper = %q( ruby -e" loop{ STDERR.puts Time.now.to_i; sleep 1 }

" )

   status, stdout, stderr =
     systemu looper do |cid|
       sleep 3
       Process.kill 9, cid
     end

   p [ status, stdout, stderr ]

~ > ruby samples/f.rb

 [#<Process::Status: pid=9985,signaled(SIGKILL=9)>, "",

“1162599744\n1162599745\n1162599746\n1162599747\n”]

-a

9

On 1/2/07, Tom P. [email protected] wrote:

And it won’t. That’s bourne-shell syntax.

It’s also cmd.exe syntax, so it /should/ work in Windows, too.

http://www.microsoft.com/technet/archive/winntas/deploy/prodspecs/
shellscr.mspx?mfr=true

I’ve found that on winblows, one must invoke cme.exe /c “command” to
get redirection to work properly.

Mike

10

On Jan 1, 2007, at 6:28 PM, Michael P. Soulier wrote:

On 1/1/07, Robert J. [email protected] wrote:

A similar question: assuming a standard Ruby install (that is, no
popen4), what’s the most robust way of running a shell command and
capturing STDOUT and STDERR?
command 2>&1 seems to not always work on Windows.

And it won’t. That’s bourne-shell syntax.

It’s also cmd.exe syntax, so it /should/ work in Windows, too.

http://www.microsoft.com/technet/archive/winntas/deploy/prodspecs/
shellscr.mspx?mfr=true

TomP