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I have a perl script which performs multiple external commands and prints the outputs from STDERR and STDOUT to a logfile along with a series of my own print statements to act as documentation on the process.

My problem is that the STDERR repeats ~identical prints as example below. I'd like to capture this before it prints and replace with the final result for each of the commands i run.

blocks evaluated : 0
blocks evaluated : 10000
blocks evaluated : 20000
blocks evaluated : 30000
...
blocks evaluated : 3420000
blocks evaluated : 3428776

Here's how I'm getting STDOUT and STDERR

my $logfile = "Logfile.log";     #log file name
#--- Open log file for append if specified ---
if ( $logfile ) 
  {
    open ( OLDOUT, ">&", STDOUT )  or die "ERROR: Can't backup STDOUT location.\n";
    close STDOUT;
    open ( STDOUT, ">", $logfile ) or die "ERROR: Logfile [$logfile] cannot be opened.\n"; 
  }

if ( $logfile ) 
  { 
    open ( OLDERR, ">&", STDERR ) or die "ERROR: Can't backup STDERR location.\n";
    close STDERR;
    open ( STDERR, '>&STDOUT'   ) or die "ERROR: failed to pass STDERR to STDOUT.\n";
  }

and closing them

close STDERR;  
open ( STDERR, ">&", OLDERR ) or die "ERROR: Can't fix that first thing you broke!\n";
close STDOUT; 
open ( STDOUT, ">&", OLDOUT ) or die "ERROR: Can't fix that other thing you broke!\n";

How do I access the STDERR when each print is occurring to do the replace? Or prevent it from printing if it isn't the last of the batch.

Many Thanks in advance.

MicrobicTiger
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  • I'm thinking this might be a good place to start: http://perldoc.perl.org/perlipc.html#Bidirectional-Communication-with-Yourself . Pipe STDERR to a forked process, and filter those lines. – kjprice Jul 02 '13 at 23:52
  • This sounds like a good place for Capture::Tiny, to capture STDERR or perhaps you can run your script with IPC::Run to redirect STDERR to a function. – MkV Jul 03 '13 at 03:32

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