From: Jeremy Bopp <jeremy@...>
Date: 2010-10-08T04:21:27+09:00
Subject: Re: popen hangs out for user input

On 10/7/2010 2:07 PM, Jeremy Bopp wrote:
> On 10/7/2010 1:40 PM, felix.leg wrote:
>> Hi,
>>
>> I want to use Ruby with latex,so I wrote a simple program which waits
>> for "\typein" command called from pdflatex:
>>
>> <CODE>
>> #!/usr/bin/ruby
>>
>> file = IO.popen('pdflatex -interaction scrollmode test.tex','r+') #1
>>
>> until file.readline.include? 'typein'; end
>> file.write "a line from RUBY"
>> file.readlines #2
>> file.close
>> </CODE>
>>
>> If I run the command from #1 in a sheel it works right: scrolls
>> "standard" latex asks, and stops for my "\@typein=". After I answer it
>> continues normally.
>>
>> But when I want do the same in Ruby with above code, it hangs out
>> waiting for input. It looks like #2 causes this, but I don't know why...
> 
> It's probably because the write buffer for the pipe is not being
> flushed.  My preferred option to fix this sort of thing is to make the
> file object synchronous:
> 
> file = IO.popen(.....)
> file.sync = true
> 
> However, you might prefer to explicitly flush things instead:
> 
> file.write(.....)
> file.flush
> ...
> file.write(.....)
> file.write(.....)
> file.flush

One more thing: you may need to insert a newline at the end of the
strings you write or use #puts instead of #write.  Most interactive
programs like this expect a newline character to flag the end of data
entry for a field.

-Jeremy