Question about run external program in Ruby

ruby-talk
1

I use this method to run a external program in ruby:

io=IO.popen("lsa 2>&1")do |f|
   while line =f.gets do
       puts line
   end
end

I can get both stdout and stderr output but how can I get the command
return value?

thanks.

···

--
Posted via http://www.ruby-forum.com/.

2

Check $?.exitstatus

···

On Mon, Jan 5, 2009 at 8:08 AM, Zhao Yi <youhaodeyi@gmail.com> wrote:

I use this method to run a external program in ruby:

io=IO.popen("lsa 2>&1")do |f|
  while line =f.gets do
      puts line
  end
end

I can get both stdout and stderr output but how can I get the command
return value?

thanks.
--
Posted via http://www.ruby-forum.com/\.

--
Andrew Timberlake
http://ramblingsonrails.com
http://www.linkedin.com/in/andrewtimberlake

"I have never let my schooling interfere with my education" - Mark Twain

3

Try the following:
io=IO.popen("ruby some_file_that_doesnt_exist")do |f|
  while line =f.gets do
      puts line
  end
end
puts $?.exitstatus
#returns - 1

···

On Mon, Jan 5, 2009 at 8:08 AM, Zhao Yi <youhaodeyi@gmail.com> wrote:

I use this method to run a external program in ruby:

io=IO.popen("lsa 2>&1")do |f|
  while line =f.gets do
      puts line
  end
end

I can get both stdout and stderr output but how can I get the command
return value?

thanks.
--
Posted via http://www.ruby-forum.com/\.

--
Andrew Timberlake
http://ramblingsonrails.com
http://www.linkedin.com/in/andrewtimberlake

"I have never let my schooling interfere with my education" - Mark Twain

4

Andrew Timberlake wrote:

Check $?.exitstatus

I found that $?.exitstatus always return 0.

···

--
Posted via http://www.ruby-forum.com/\.

5

How can I get stderr in this method?

···

--
Posted via http://www.ruby-forum.com/.

6

Zhao Yi wrote:

How can I get stderr in this method?

You are already combining stderr with stdout (2>&1)

To get them separately, see open3.rb in the standard library.

# Open3 grants you access to stdin, stdout, and stderr when running
another
# program. Example:

···

#
# require "open3"
# include Open3
#
# stdin, stdout, stderr = popen3('nroff -man')
#
# Open3.popen3 can also take a block which will receive stdin, stdout
and
# stderr as parameters. This ensures stdin, stdout and stderr are
closed
# once the block exits. Example:
#
# require "open3"
#
# Open3.popen3('nroff -man') { |stdin, stdout, stderr| ... }

However, since it forks twice, I believe you lose the exit status from
the (grand)child. You also need to be careful not to block on reading
from stdout when the child has written a large amount of data to stderr,
or vice versa. (For example, you could use select, or you could have two
separate threads reading from stdout and stderr)
--
Posted via http://www.ruby-forum.com/\.

7

Another option is the open4 gem. See
http://www.codeforpeople.com/lib/ruby/open4/open4-0.9.6/README
and scroll down to SAMPLES

···

--
Posted via http://www.ruby-forum.com/.