Nesh has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks I am running an application from script and then as the application progresses it keeps on displaying various things on the command prompt which I am trying to capture to a log file. For experimentation I used a batch file and opened it using pipe (I plan to do the same with exe). the code looks like 
use Log::Log4perl qw();
Log::Log4perl->init("process.conf");
my $log = Log::Log4perl->get_logger();

open APP, "Exception.bat |" or die "File not found\n";

while(<APP>){
        print;
    #log->info;
}
close APP;

print "Out of batch file\n";

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Now when I capture everything through print then it works fine...but as soon as I try to use logging it fails. Please advise. Thanks

Replies are listed 'Best First'.
Re: Running an application and capturing output
by mifflin (Curate) on Jun 02, 2005 at 02:21 UTC
    Like thunderkgnat says, you're probably missing the $ infront of log->info;
    deparsing that code 
    C:\Documents and Settings\erickn\Desktop\invexp>perl -MO=Deparse -e"lo
+g->info"
log($_)->info;
-e syntax OK

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    shows that you are executing log, a builtin function of perl. Since $_ is not set it tries to do a log of 0 which is not defined.
    Try putting use strict; and use warnings; at the top of your script to help track down bugs like these.
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[d/l]

      Why would $_ not be set in a while loop? What would either strict or warnings do in a case like this?

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[d/l]
        Strict because, well, it's just a good idea.
        Warnings because, if he had it on, would probably have seen something like 
        C:\Documents and Settings\erickn\Desktop\invexp>e.pl
line 1
Can't take log of 0 at C:\Documents and Settings\erickn\Desktop\invexp
+\e.pl line 9, <DATA> line 1.

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        Note that I am guessing what his batch file would return to stdout. My test code to produce the above output... 
        #use warnings;
use strict;
use Log::Log4perl qw();
Log::Log4perl::init("process.conf");
my $log = Log::Log4perl->get_logger();
#open APP, "Exception.bat |" or die "File not found\n";
while(<DATA>){
    print;
    log->info;
}
print "Out of batch file\n";
__DATA__
line 1
line 2

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        update: I suppose that's not alot of extra info but it is more that he had and might have made it easier for him to figure it out on his own. *shrugs*
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[d/l]
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Re: Running an application and capturing output
by moot (Chaplain) on Jun 02, 2005 at 01:33 UTC
    You don't specify what the failure is, but it looks from your commented out line that you are not actually passing any data to $log->info. Try: 
    # rest of code

 $log->info($_);

# rest of code

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[d/l]
Re: Running an application and capturing output
by thundergnat (Deacon) on Jun 02, 2005 at 01:35 UTC

    It doesn't appear that $log->info will act on $_ by default. Try explicitly passing $_ to it.

    while(<APP>){
        print;
        $log->info($_);
}

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[d/l]
      I tried that also...but that was also giving the same error. The error looks like 
      C:\Neshat\Perl-Scripts>perl captureexeoutput.pl
Can't take log of 0 at captureexeoutput.pl line 8, <APP> line 1.
FINDSTR: Write error
The process tried to write to a nonexistent pipe.
The process tried to write to a nonexistent pipe.
The process tried to write to a nonexistent pipe.
The process tried to write to a nonexistent pipe.
The process tried to write to a nonexistent pipe.
^C^C
C:\Neshat\Perl-Scripts>

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[d/l]

        Do you have the $ sigil on your variable? It isn't in your example. log is a function. $log is the name of your Logger.

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