I'm writing a Ruby script to run Lua code for TextMate. Using:
output = `lua #{filename}`
works when the file prints happily, but when an error occurs (e.g. a
syntax error in the file) the error message is printed to stderr (I
think) and 'escapes' my capture.
How/can I catch output to stderr from another system command? (I want
to use the output later, I just don't want it spat out at that point.)
You could do:
output = `command 2>&1`
However, now $stderr is mixed in with $stdout.
-- Daniel
On Mar 1, 2006, at 6:43 PM, Phrogz wrote:
How/can I catch output to stderr from another system command? (I want
to use the output later, I just don't want it spat out at that point.)
harp:~ > gem install session >/dev/null 2>&1 && echo 'success'
success
harp:~ > cat a.rb
require 'rubygems'
require 'session'
sh = Session::new
command = %Q( ruby -e" STDERR.puts :stderr; STDOUT.puts :stdout " )
stdout, stderr = sh.execute command
require 'yaml'
y "stdout" => stdout
y "stderr" => stderr
y "sh.status" => sh.status
harp:~ > ruby a.rb
On Thu, 2 Mar 2006, Phrogz wrote:
I'm writing a Ruby script to run Lua code for TextMate. Using:
output = `lua #{filename}`
works when the file prints happily, but when an error occurs (e.g. a
syntax error in the file) the error message is printed to stderr (I
think) and 'escapes' my capture.How/can I catch output to stderr from another system command? (I want
to use the output later, I just don't want it spat out at that point.)
---
stdout: |
stdout
---
stderr: |
stderr
---
sh.status: 0
-a
--
judge your success by what you had to give up in order to get it.
- h.h. the 14th dali lama
That'll do for now, thanks! 
That's awesome, ara. Unfortunately, I need to write something that will
work on random MacOS machines witj a default Ruby install. Can I poke
about in the innards of session and steal ideas/code?
You may want to check out IO.popen and IO.popen3 (or is it popen2? I can never remembr the numbers)
On Mar 1, 2006, at 1:58 PM, Phrogz wrote:
That'll do for now, thanks!
absolutely. basically what you're after is open3 - it's in the stdlib and
will probably suffice. session is overkill if you're not running multiple
commands per session (no pun intended) anyhow.
anyhow, here's the essence:
harp:~ > cat a.rb
def spawn command, opts = {}
require 'open3'
stdin = opts.values_at(:stdin, 'stdin', 0).compact.first
stdout = opts.values_at(:stdout, 'stdout', 1).compact.first
stderr = opts.values_at(:stderr, 'stderr', 2).compact.first
Open3::popen3(command) do |i,o,e|
i << stdin if stdin
i.close # important!
o.each{|line| stdout << line} if stdout
e.each{|line| stderr << wrine} if stderr
end
$?.exitstatus
end
stdout, stderr = '', ''
exitstatus = spawn 'cat', 0=>42, 1=>stdout, 2=>stderr
require 'yaml'
y 'exitstatus' => exitstatus,
'stdout' => stdout,
'stderr' => stderr
harp:~ > ruby a.rb
On Thu, 2 Mar 2006, Phrogz wrote:
That's awesome, ara. Unfortunately, I need to write something that will
work on random MacOS machines witj a default Ruby install. Can I poke
about in the innards of session and steal ideas/code?
---
stdout: "42"
stderr: ""
exitstatus: 0
regards.
-a
--
judge your success by what you had to give up in order to get it.
- h.h. the 14th dali lama
Thanks so much, Ara. That's almost perfect, except that the exitstatus
seems to be eaten. No matter what happens, I get a clean 0 exitstatus.
For example:
require 'open3'
`lua xxx`
#=> lua: cannot open xxx: No such file or directory
p $?.exitstatus
#=> 1
output, errors = '', ''
p Open3::popen3( "lua xxx" ){ |i,o,e|
i.close
o.each { |line| output << line }
e.each { |line| errors << line }
$?.exitstatus
}
#=> 0
I can mostly infer the failure based on whether or not messages came to
stderr, but it'd be nice to know for sure.
right you are. if you check out ruby-1.8.4/lib/open3.rb you'll see :
...
pid = fork{
# child
fork{
# grandchild
...
}
exit!(0) # check this out
}
...
so you'll never see an error. my open 4 package fixes this - i actually just
made a release a few weeks ago to support throwing and exception when the exec
fails. here's an example (it's on rubyforge):
harp:~ > cat a.rb
IO::popen("gem install open4 -r -y"){|pipe| pipe.read} and puts "installed open4..."
require "rubygems"
require "open4"
def spawn cmd, opts = {}
getopt = lambda{|o,*d| opts[o] || opts[o.to_s] || opts[o.to_s.intern] || d.shift}
stdin = getopt["stdin"] || getopt[0, ""]
stdout = getopt["stdout"] || getopt[1, ""]
stderr = getopt["stderr"] || getopt[2, ""]
Open4::popen4(cmd) do |cid,i,o,e|
stdin.each{|line| i << line}
i.close
o.each{|line| stdout << line }
e.each{|line| stderr << line }
end
[$?.exitstatus, stdout, stderr]
end
bt =
lambda{|e| STDERR.puts %Q[#{ e.message } (#{ e.class })\n#{ e.backtrace.join "\n" }\n]}
argvs =
["fubar"],
["ruby does-not-exist"],
["ruby", {"stdin" => "p 42"}]
argvs.each do |argv|
cmd, opts = argv
puts
puts "--- spawn( #{ cmd.inspect }, #{ opts.inspect } ) ---"
p( spawn(*argv) ) rescue bt[$!]
puts
end
harp:~ > ruby a.rb
installed open4...
--- spawn( "fubar", nil ) ---
No such file or directory - fubar (Errno::ENOENT)
/home/ahoward//lib/ruby/site_ruby/1.8/open4.rb:75:in `exec'
/home/ahoward//lib/ruby/site_ruby/1.8/open4.rb:75:in `popen4'
/home/ahoward//lib/ruby/site_ruby/1.8/open4.rb:57:in `popen4'
a.rb:11:in `spawn'
a.rb:36
a.rb:32
--- spawn( "ruby does-not-exist", nil ) ---
[1, "", "ruby: No such file or directory -- does-not-exist (LoadError)\n"]
--- spawn( "ruby", {"stdin"=>"p 42"} ) ---
[0, "42\n", ""]
hth.
i'd sure like to get this in the stdlib...
-a
On Sat, 4 Mar 2006, Phrogz wrote:
Thanks so much, Ara. That's almost perfect, except that the exitstatus
seems to be eaten. No matter what happens, I get a clean 0 exitstatus.
For example:require 'open3'
`lua xxx`
#=> lua: cannot open xxx: No such file or directoryp $?.exitstatus
#=> 1output, errors = '', ''
p Open3::popen3( "lua xxx" ){ |i,o,e|
i.close
o.each { |line| output << line }
e.each { |line| errors << line }
$?.exitstatus
}
#=> 0I can mostly infer the failure based on whether or not messages came to
stderr, but it'd be nice to know for sure.
--
judge your success by what you had to give up in order to get it.
- h.h. the 14th dali lama
