Perl: library to log on specific files - perl

Question

I'm creating a library for my stuffs where I want to log errors on a specific file. Unfortunately, while it works if I initiate only one single instance of the library, it doesn't if I initiate more than one instance.
The results in that case is that the output is logged all in the last file and not half and half as I was expecting.
This is the main.pl
eval 'exec /usr/bin/perl -I `pwd` -S $0 ${1+"$#"}'
if 0;
use strict;
use MyLibrary;
my ($rc, $test_2, $test_1);
# The output is not going into this file
exit $test_1 if (($test_1 = MyLibrary->new("/tmp", "test_1")) !~ "HASH");
# It is going all into this file
exit $test_2 if (($test_2 = MyLibrary->new("/tmp", "test_2")) !~ "HASH");
exit $rc if ( $rc = $test_1->test() );
exit $rc if ( $rc = $test_2->test() );
and this is MyLibrary.pm
package MyLibrary;
use strict;
use Symbol;
use vars qw($VERSION #ISA #EXPORT %default);
#EXPORT = qw(
);
$VERSION = '1.00';
require 5.000;
%default;
my $fh;
sub new
{
my $rc;
my ($proto, $log_dir, $log_file) = #_;
my $class = ref($proto) || $proto;
my $self = { %default };
bless($self, $class);
$fh = gensym;
($self->{'log_dir'}, $self->{'log_file'}) = ($log_dir, $log_file);
return $rc if ( $rc = $self->open_log_file() );
return $self;
}
sub destroy
{
my $rc;
my $self = shift;
return $rc if ( $rc = $self->close_log_file() );
}
sub open_log_file
{
my $self = shift;
open $fh, ">>$self->{'log_dir'}/$self->{'log_file'}" or die "cannot open file $self->{'log_dir'}/$self->{'log_file'}";
return 0;
}
sub close_log_file
{
my $self = shift;
close($fh) or die "cannot close $self->{'log_dir'}/$self->{'log_file'}";
return 0;
}
sub test
{
my $self = shift;
print $fh "[$self->{'log_file'}]\n";
return 0;
}
1;
One more thing ... In this example, I'm using $fh as a global variable, while I would like to have this variable part of the %default hash. However, if I try to make it part of the hash replacing all the $fh occurences with $self->{'fh'}, I get the following error:
String found where operator expected at MyLibrary.pm line 75, near "} "[$self->{'log_file'}]\n""
(Missing operator before "[$self->{'log_file'}]\n"?)
syntax error at MyLibrary.pm line 75, near "} "[$self->{'log_file'}]\n""
Row 75 in this case will be the following:
sub test
{
my $self = shift;
Row 75 =>>> print $self->{'fh'} "[$self->{'log_file'}]\n";
return 0;
}
While the full library reviewed accordingly is:
package MyLibrary;
use strict;
use Symbol;
use vars qw($VERSION #ISA #EXPORT %default);
#EXPORT = qw(
);
$VERSION = '1.00';
require 5.000;
%default;
sub new
{
my $rc;
my ($proto, $log_dir, $log_file) = #_;
my $class = ref($proto) || $proto;
my $self = { %default };
bless($self, $class);
$self->{'fh'} = gensym;
($self->{'log_dir'}, $self->{'log_file'}) = ($log_dir, $log_file);
return $rc if ( $rc = $self->open_log_file() );
return $self;
}
sub destroy
{
my $rc;
my $self = shift;
return $rc if ( $rc = $self->close_log_file() );
}
sub open_log_file
{
my $self = shift;
open $self->{'fh'}, ">>$self->{'log_dir'}/$self->{'log_file'}" or die "cannot open file $self->{'log_dir'}/$self->{'log_file'}";
return 0;
}
sub close_log_file
{
my $self = shift;
close($self->{'fh'}) or die "cannot close $self->{'log_dir'}/$self->{'log_file'}";
return 0;
}
sub test
{
my $self = shift;
print $self->{'fh'} "[$self->{'log_file'}]\n";
return 0;
}
1;

Answer 1

Empirically, it seems that the file handle in a print statement cannot be an arbitrary expression. This is really only a minor modification of your code, but to get MyLibrary.pm to compile, I replaced:
print $self->{'fh'} "[$self->{'log_file'}]\n";
with:
my $fh = $self->{'fh'};
print $fh "[$self->{'log_file'}]\n";
There are some other minor tweaks, but this code worked for me:
MyLibrary.pm
package MyLibrary;
use warnings;
use strict;
use vars qw($VERSION #ISA #EXPORT %default);
#EXPORT = qw();
$VERSION = '1.00';
require 5.000;
sub new
{
my ($proto, $log_dir, $log_file) = #_;
my $class = ref($proto) || $proto;
my $self = { %default };
bless($self, $class);
$self->{'log_dir'} = $log_dir;
$self->{'log_file'} = $log_file;
$self->open_log_file();
return $self;
}
sub destroy
{
my $rc;
my $self = shift;
return $rc if ( $rc = $self->close_log_file() );
}
sub open_log_file
{
my $self = shift;
my $log_file = "$self->{log_dir}/$self->{log_file}";
open $self->{'fh'}, ">>", $log_file or die "cannot open file $log_file";
return;
}
sub close_log_file
{
my $self = shift;
close($self->{'fh'}) or die "cannot close $self->{'log_dir'}/$self->{'log_file'}";
return;
}
sub print_data
{
my $self = shift;
my $fh = $self->{fh};
print $fh #_, "\n";
}
sub test
{
my $self = shift;
my $fh = $self->{'fh'};
print $fh "[$self->{'log_file'}]\n";
return 0;
}
1;
I'm not convinced that the use 5.000; buys you very much. The chances of finding a Perl 4.x still running are pretty remote. These days, anything earlier than Perl 5.8 is long dead (or, if it isn't, it should be).
There are many minor improvements that could be made in the code that are not shown above.
testcase.pl
#!/usr/bin/env perl
use warnings;
use strict;
use MyLibrary;
my ($rc, $test_2, $test_1);
my $counter = 0;
sub counter
{
printf"OK %d\n", ++$counter;
}
counter;
# The output is not going into this file
exit $test_1 if (($test_1 = MyLibrary->new("/tmp", "test_1")) !~ "HASH");
counter;
# It is going all into this file
exit $test_2 if (($test_2 = MyLibrary->new("/tmp", "test_2")) !~ "HASH");
counter;
exit $rc if ( $rc = $test_1->test() );
counter;
exit $rc if ( $rc = $test_2->test() );
counter;
$test_1->print_data("Extra information");
$test_2->print_data("Missing syncopation");
print "Finished\n";
Nth Sample Run
It looks like I ran a previous edition of testcase.pl once, before adding the print_data function, and four times since adding the print_data function.
$ perl -I$PWD testcase.pl
OK 1
OK 2
OK 3
OK 4
OK 5
Finished
$ cat /tmp/test_1
[test_1]
[test_1]
Extra information
[test_1]
Extra information
[test_1]
Extra information
[test_1]
Extra information
$ cat /tmp/test_2
[test_2]
[test_2]
Missing syncopation
[test_2]
Missing syncopation
[test_2]
Missing syncopation
[test_2]
Missing syncopation
$