Re: parsing Makefiles

[Andrew Gaffney]

David le Blanc wrote:
From: Andrew Gaffney [mailto:[EMAIL PROTECTED] 
Sent: Monday, 23 February 2004 12:35 AM
To: David le Blanc
Cc: [EMAIL PROTECTED]
Subject: Re: parsing Makefiles

David le Blanc wrote:

From: Andrew Gaffney [mailto:[EMAIL PROTECTED] 
Sent: Sunday, 22 February 2004 6:09 PM
To: David le Blanc
Cc: [EMAIL PROTECTED]
Subject: Re: parsing Makefiles

David le Blanc wrote:


I've come up with some *simple* code that seems to work:

#!/usr/bin/perl

use strict;
use warnings;
$| = 1;
my $total = `make -n | wc -l`;
my ($count, $line);
open MAKE, "make |";
foreach $line (<MAKE>) {
$count++;
my $percent = int(($count / $total) * 100);
print "..$percent";
}


You may find that the 'MAKE' file handle is buffered by the make
application.
I order to ensure 'make' doesn't buffer its output, you 
need to run it


in its
own pseudo-terminal.   The Expect module may be able to 
help, since it


runs
apps in pseudo-terminals, or someone else may offer a 
better solution.

Its not the 'make' output that's being buffered. That doesn't 
get printed at all. Its my 
output that does appear until the whole run is done.
Ok,  Lets break down what is really going on here.

Your  loop construct:

foreach $line (<MAKE>) {
        .. print stuff ..
}

is looping BASED ON THE OUTPUT of the make command.  

Since the MAKE COMMAND OUTPUT is being buffered by the make command,
you will find that NOTHING arrives in the 'foreach' loop until the
entire 
make has complete and FLUSHED its output.

Hence, if you want to print output as the MAKE COMMAND 
OUTPUT arrives,

you
must make sure the COMMAND OUTPUT arrives in a timely manner.. I.e.
unbuffered.
I understand. I modified my code to verify this:

#!/usr/bin/perl

use strict;
use warnings;
#$| = 1;
my $total = `make -n | wc -l`;
print "$total\n";
my ($count, $line);
open MAKE, "make |";
foreach $line (<MAKE>) {
  $count++;
  my $percent = int(($count / $total) * 100);
#  print "..$percent";
  print $line;
}
This waited until the end to print all the output. Although, 
if I do something like 'make 
| less' on the command line, the output is not buffered. So, 
is Perl buffering the output 
from MAKE in this case?


Close, but not quite.  perl is handing the data to your script as soon
as it
arrives from the make command.  The make command on the otherhand has
realised you
are not using a TTY, but are in fact directing the output to a pipe or
file, so
it buffers the contents internally.
That doesn't make sense. When it pipes through less, as far as 'make' knows, its not 
outputting to a TTY anymore. Piping output through Perl should be the same as piping to 
less as far as 'make' is concerned.

Try the following.   

In one window, touch 'make.log', and then run 'tail -f make.log'

In another window, run 'make >> make.log'

If the output appears as it does when using less, then it is perl that
is
buffering the output, so add to your script:
The output appears just as it did with 'make | less'.

# at the top
use IO::Handle;
# after the open
MAKE->autoflush(0);
This doesn't work. Same results still. I double-checked that Perl wasn't buffering my 
output by having it print localtime() with each output. I get ~30 lines of the same time. 
Does Perl try to read the entire 'file' in before it sticks it into the array? This would 
make sense. Perl could be waiting for the 'file' to 'close' ('make' to finish running) 
before it starts chopping up the output.

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