piping output and getting return value (was: parsing Makefiles)

[Andrew Gaffney]

Andrew Gaffney wrote:
zsdc wrote:

Andrew Gaffney wrote:

I tried that and it still spits out all the output at the end. Here's 
my current code:

#!/usr/bin/perl

use strict;
use warnings;
$| = 1;
my $total = `make -n | wc -l`;
print "$total\n";
my ($count, $line);
open MAKE, "make |" or die "Can't open MAKE pipe";
foreach (<MAKE>) {
  $count++;
  my $percent = int(($count / $total) * 100);
#  print "${percent}...";
  print $_;
}


First of all, using foreach will _always_ wait for all of the data 
before doing anything else, no matter what, so first change:

  foreach (<MAKE>) {

to:

  while (<MAKE>) {

and then try to find out if maybe it is indeed being buffered, though 
$| won't help you here, as it sets autoflushing on output, not input.

Another thing is that "make" is probably going to print much more 
lines than "make -n" because "make -n" only prints the commands to be 
executed while those commands themselves are likely to produce some 
output as well, unless all of them are run with >/dev/null 2>&1 at the 
end.

Try running this program:

#!/usr/bin/perl

use strict;
use warnings;
$| = 1;
my $total = `make -n | wc -l`;
my $count = 0;
open MAKE, "make 2>/dev/null |" or die "Can't open MAKE pipe";
while (<MAKE>) {
  $count++;
  my $percent = int(($count / $total) * 100);
  print "$percent%\r";
}
print "Done.\n";
__END__
Does it work? Keep in mind that unless every command in your Makefile 
ends with >/dev/null you will get values greater than 100%.


Ok, so it was the 'foreach' causing my problem the whole time. Here is 
my current code:

#!/usr/bin/perl

use strict;
use warnings;
$| = 1;
my $total = `make -n | wc -l`;
my $count = 0;
open MAKE, "make |" or die "Can't open MAKE pipe";
while (<MAKE>) {
  $count++;
  my $percent = int(($count / $total) * 100);
  print "\r${percent}% ";
}
print "\n";
This code works just fine providing that the Makefile commands don't 
output anything. Although, most Makefiles don't output anything except 
the commands being executed (which is covered by 'make -n' and compile 
errors. My next step is to add a "scrollback buffer" in order to display 
compile errors. I was thinking about something like:
<snip>
Would that work to keep the last 15 lines of output?
The following works for the scrollback buffer:

#!/usr/bin/perl

use strict;
use warnings;
$| = 1;
my $total = `make -n | wc -l`;
my $count = 0;
my (@buffer, $line);
open MAKE, "make |" or die "Can't open MAKE pipe";
while (<MAKE>) {
  $count++;
  $line = "$count - $_";
  if($#buffer < 14) {
    push @buffer, $line;
  } else {
    for(my $tmp=1;$tmp<15;$tmp++) {
      $buffer[($tmp-1)] = $buffer[$tmp];
    }
    $buffer[14] = $line;
  }
  my $percent = int(($count / $total) * 100);
  print "\r${percent}% ";
}
print "\n";
foreach $line (@buffer) {
  print $line;
}
Now, my question is how do I get the return value of 'make' once the process terminates 
with the above code? I want the program to dump the "buffer" when 'make' returns an error 
code.

--
Andrew Gaffney
Network Administrator
Skyline Aeronautics, LLC.
636-357-1548
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