[ruby-talk:21502] Re: Interaction system() / $stdout ?

At 02:39 PM 9/20/01, you wrote:
>This appears to work:
>
>$saved_stdout = $stdout.dup
>$stdout = File.open("log-file", "w")
>system "echo After redirect, to log-file I hope."
>$stdout = $saved_stdout.dup
>system "echo Original restored, to STDOUT I hope."
>
>I'm not sure why that second "dup" is necessary, perhaps a guru can
>elaborate or give a better solution.

I think the solution needs to be more complicated. Try closing the logfile 
before restoring stdout:

$saved_stdout = $stdout.dup
$stdout = File.open("log-file", "w")
system "echo After redirect, to log-file I hope."
$stdout.close   ###### New line
$stdout = $saved_stdout.dup          ### this is line 5
system "echo Original restored, to STDOUT I hope."

The result of the system is this:

test4.rb:5: closed stream (IOError)

Note that the line number is the second assignment to stdout, not the 
attempt to write to it.

It seems you have to stash the stream in a temp, reassign stdout, and then 
close stdout:

$saved_stdout = $stdout.dup
$stdout = File.open("log-file", "w")
puts "echo After redirect, to log-file I hope."
$saved_internal_stdout = $stdout    ###### New line
$stdout = $saved_stdout.dup
$saved_internal_stdout.close   ###### New line
puts "echo Original restored, to STDOUT I hope."

By the way, it doesn't seem to me that the second dup is needed. Seems to 
work without it. Why do you think it's needed?

This is all complicated enough that I'm going to extend my Fluid variables 
package to handle it:

     Fluid.redirect(["$stdout", File.open("logfile", 'w')]) {
       puts "this goes to the logfile"
     }
     puts "this goes back to the old $stdout"

But I'd like to know if the above sequence of steps really works, or just 
doesn't obviously fail.

--
Brian Marick, [e-mail]
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