Greetings, esteemed monks!

I've been toying with different ways of capturing STDERR separately from STDOUT and doing a quick transformation of it, to give it "big","em",and "strong" elements to it for display of the whole output of a cron job.

You can see a node (my first question here as an Anonymous Monk) that got me started here: Prepending a string to STDERR output, and logging STDOUT & STDERR synchronously to a file

So one of my main questions is, is there any benefit to using scalars as arguments to open3()?

For example (my apologies for all the commented-out print statements),

my $cmdin=gensym;
my $cmdout=gensym;
my $cmderr=gensym;
eval{
  $pid = open3($cmdin, $cmdout, $cmderr, $cmd);
  #$val = waitpid(-1,0);
};
die "Exception raised in block using open3: $@\n" if $@;
$selector = IO::Select->new();
$selector->add($cmdout, $cmderr);
#print "After selector->add\n";
while (@ready=$selector->can_read){
    #print "In while loop\n";
    foreach $fh (@ready) {
        #print "In foreach loop; fh is $$fh.\n";
        my $byte;
    my @line;
    while ((sysread($fh, $byte, 1) == 1) && ($byte ne "\n")){push(@lin
+e,$byte);};
        #$line = scalar <$fh>;
    #print "line we just read in is $line";
    if (@line){
      my $line2=join("",@line);
      #added <strong> here JWC 5/9/06
      #print "Printing $line to log:\n";
      #print "printing $$fh output to log\n";
      if (fileno($fh) == fileno($cmderr)) {print LOG "<em><strong><big
+>STDERR: $line2</big></strong></em>\n";}
      else {print LOG "$line2\n";}
      #print "printed $$fh output to log\n";
    }
    else{
      #print "the line variable was empty--removing $$fh from selector
+.\n";
      $selector->remove($fh);
      #print "removed $$fh from selector\n";
    }
    #print "at end of foreach loop.\n";
    }
    #print "at end of while loop.\n";
}
close($cmdout)|| warn "Error:  Could not close $$cmdout: $!";
close($cmderr)|| warn "Error:  Could not close $$cmderr: $!";
print LOG "*-*-end_run-*-*\n";
close(LOG);
[download]

vs.

$pid = open3(*CMD_IN, *CMD_OUT, *CMD_ERR, $cmd);
close(CMD_IN);

$SIG{CHLD} = sub {
    print "REAPER: status $? on $pid\n" if waitpid($pid, 0) > 0
};

$selector = IO::Select->new();
$selector->add(*CMD_ERR, *CMD_OUT);

while (@ready = $selector->can_read) {
    foreach $fh (@ready) {
    $line = scalar <$fh>;
    if (fileno($fh) == fileno(CMD_ERR)) {print "STDERR: ", $line}
    else {print "STDOUT: ", $line}
    ($line) || $selector->remove($fh);
    }
}

close(CMD_OUT);
close(CMD_ERR);
[download]

Now one thing I have head is to never mix synch and asych i/o, in other words the $selector-can_read uses select(), which uses asynch IO, I believe, but $line=scalar<$fh> uses synchronous? I dunno, I came up with a kloogy solution to that so I'd like to know also what's the best practice. I've had more luck with the first variation than the second, so far.

Note that a lot of the commented out part was stuff that I tried based on doing some searches on here about the behavior of open3().

A test script I've been using follows:

#!/opt/local/bin/perl

$|++;
print "1:  I am great!\n";
print "2:  I am great!\n";
warn "3:  Warning:  I am great!\n";
print "4:  I am great!\n";
[download]

_________________________________________________________________________________

Without me, it's just aweso

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