package Logger::Simple;
use strict;
use Carp;
use FileHandle;
use Fcntl qw(:flock);
use vars qw /$VERSION $SEM/;

$VERSION='1.06';
$SEM = ".LS.lock";

sub new{
  my($class,%args)=@_;
  my $self =  bless{LOG        => $args{LOG} || croak"No logfile!\n",
                    CARP       => $args{CARP} || undef,
                    FILEHANDLE => new FileHandle || croak"Unable to ge
+t filehandle\n",
                    SEMAPHORE  => new FileHandle || croak"Unable to cr
+eate semaphore filehandle\n",
                    ERROR      => "",
                    HISTORY    => [],
              },$class;

  if(! $self->open()){
        die"Unable to open $self->{LOG}\n";
  }

  return $self;
}

sub open{
  my $self=shift;
  if(! open($$self{FILEHANDLE},">>$$self{LOG}")){
    $self->set("Unable to open logfile\n");
    return 0;
  }
  $$self{FILEHANDLE}->autoflush(1);
  return 1;
}

sub write{
  my($self,$msg)=@_;
  my $FH=*{$$self{FILEHANDLE}};

  my $format="$0 : [".scalar (localtime)."] $msg";
  $self->lock();
  if(! print $FH "$format\n"){
        $self->set("Unable to write to $$self{LOG}: $!\n");
  }
  $self->unlock();
}

sub message{
  my $self=shift;

  if(wantarray){
    my @messages=@{$$self{HISTORY}};
    return @messages;
  }else{
    my $message=$$self{ERROR};
    return $message;
  }
}

sub clear{
  my $self=shift;
  $$self{ERROR}=undef;
}

sub set{
    my ($self,$error)=@_;
  $self->clear;
  $$self{ERROR}=$error;

  push @{$$self{HISTORY}},$error;
  carp "$error\n" if $$self{CARP};
  $self->write($error);
}

sub print_object{
  require Data::Dumper;
  my $self=shift;
  print Data::Dumper->Dumper($self);
}

sub lock{
  my $self=shift;
  my $FH=*{$$self{SEMAPHORE}};
  if(-e $SEM){
    flock($FH,LOCK_NB) or carp"Can't obtain file lock: $!\n";
    open($FH,">$SEM")||die"Can't create lock file: $!\n";
    flock($FH,LOCK_EX) or die"Can't obtain file lock: $!\n";
  }else{
        open $FH,">$SEM"||die"Can't create lock file: $!\n";
    flock($FH,LOCK_EX) or die"Can't obtain file lock: $!\n";
  }
}

sub unlock{
  my $self=shift;
  my $FH=*{$$self{SEMAPHORE}};
  if(-e $SEM){
    flock(S,LOCK_UN);
    close S;
    unlink $SEM;
  }
}
1;
[download]

#!/opt/perl5/bin/perl
# locker.pl
use strict;
use Logger::Simple;

my $L=Logger::Simple->new(LOG=>"file.txt",CARP=>'1');

for(1..10){
  $L->write("Writing");}  

#!/opt/perl5/bin/perl -w
# writer.pl
use strict;
use Logger::Simple;

my $L=Logger::Simple->new(LOG=>"file.txt",CARP=>'1')

for(1..5){
  $L->write("Getting through?");
}

#!/bin/sh
# runner.sh

./locker.pl &
./writer.pl
[download]