Need to output the action of a system() command and have a progress indicator

Question

I have a nice progress indicator from Need a progress indicator for a Perl system() command using T:R:G mod

open(my $cmd, '-|', "$command $flags_args 2>/dev/null")
  or print "\nAttention: Command $command $flags_args failed $!"
  and return 1;

while (<$cmd>)
{
  $percentage = ($cntr/$lines) * 100;
  $percentage = 100 if $percentage > 100;

  printf("Progress: %3d%%\r", $percentage);
  $cntr++;

}
close($cmd);

Now my I want logging of the STDOUT and STDERR of the commands output. I'm not too familiar with pipe output so I tried adding:

print $LOG $cmd

and

print $LOG Dumper(\$cmd)

before the end of the while loop. It did not work. The first output

GLOB(0x11df7a0)GLOB(0x11df7a0)GLOB(0x11df7a0)

the second

$VAR1 = \\*{'::$cmd'};
$VAR1 = \\*{'::$cmd'};
$VAR1 = \\*{'::$cmd'};

Does anyone know how I can get the output from the piped $cmd? Example for a $command = make command

 Making all in src
 make[1]: Entering directory `/tmp' 
 Making all in include
 make[2]: Entering directory '/tmp/2'

 ...

Answer 1

Try making it

 print $LOG $_;

or maybe just

 print $LOG;

(since $_ is the default if nothing is specified)

To explain: $cmd is the file you're reading from; $_ is the line read from it. You can make it clearer by writing:

 while ($line = <$cmd>) {
    print $LOG $line;
    ...
 }

Answer 2

$cmd is the I/O handle to your command's output, an internal data type that doesn't make much sense to print. You want to use <$cmd> or readline($cmd) to get the output of it, which you already do in your while loop:

while (<$cmd>)      # same as:    while (defined($_ = readline($cmd)))
{
  # last line from command is now stored in $_
  print $LOG $_;

  $percentage = ($cntr/$lines) * 100;
  $percentage = 100 if $percentage > 100;

  printf("Progress: %3d%%\r", $percentage);
  $cntr++;


}