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
