What is the simple way to keep the output stream exactly as it shown out on the screen (while interactive data used) ?

Question

Hello friends,

Let's say I have the following simple script:

print "ID : ";
$ID = <>;
system (`comp program $ID`);
exec "task --shell";

When I use:

perl foo.pl | tee log.txt

The showing up problem is getting on screen a blink sign echo (waiting for the ID enter) before I even see the "ID : " (print instruction).

I need to keep on a log file all running output script (very long), notice that at the start of the run I have an interactive part that also need to be kept.

Is there a way inside PERL script or outside it, that keep the output stream exactly as it shown out on the screen, and what do you think is the simple & efficient way to conduct it?

I've noticed the IO::Tee , File::Tee moudles and Log4perl - someone can help me find the best way to use it ?

Answer 1

You could run everything inside a screen session with logging enabled.

Answer 2

The best approach I have seen is to use script program.

You run script (program) - it gives you shell. in this shell you run anything you want. When you're done, you exit this shell, and everything that was on your screen will be in typescript file. Including all control codes.

There is also "bonus" - you can replay saved session with scriptreplay.

Answer 3

It's possible that your script is asking for user input before printing the "ID: " prompt because you don't have autoflush turned on. Try adding the following:

$|++;
print "ID : ";
$ID = <>;
system (`comp program $ID`);
exec "task --shell";

If this works then you might look at the Perl documentation about output buffering. perldoc -q buffer will explain what's happening in more detail as well as show some alternate ways of turning on autoflush.

If this doesn't solve the problem then it's possible that the tee command is buffering your output. In this case I would use script or screen as suggested by depesz or Manni