STDOUT redirected externally and no output seen at the console

Question

Hi,

I have a program which reads the output from external application.The external app gives set of output .My program reads the output from this external app while($line=) and print it to STDOUT.But the "print $line STDOUT" prints only some lines and when the error has occurred ,print to STDOUT is not working , but my one more logging statement "push @arr,$line" has stored complete output from the external app.From this i got to know STDOUT is not working properly when error happens. Eg: if external app output is like:

---

Starting command

First command executed successfully

Error:123 :next command failed

Program terminated

---

In here the STDOUT prints only :

Starting command

First command executed successfully

But if i check the array it has complete output including error details.So i guessed STDOUT has been redirected or lost.

So i tried storing STDOUT in the beginning of the program to $old_handle using open and then try to restore it before print statement using select($old_handle) (thinking some thing redirects STDOUT when error happens )

But i was not successfull , i dont know what is wrong here.Please help me.

Thanks.

Answer 1

It's possible the output is being buffered. Try setting

$| = 1;

at the start of your program. This will cause the output to be displayed straight away, rather than being buffered for later.

Answer 2

Just guess, may be because error output doesn't go to STDOUT. Use redirect

first_program |& perl_program

or

first_program 2>&1 | perl_program